Category Archives: A

Auditory System

Pathways

Auditory_Pathways

  • Ventral cochlea – encodes intensity information
  • Dorsal cochlea – encodes information and analyzes quality of sounds (e.g., differentiates phonemes)
  • Organ of Corti –the auditory transductor, which consists of cells which bend in response to sound waves
  • Info from one ear may travel via a number of different routes to reach the auditory cortex of both hemispheres
  • Central Auditory Pathways are Unlike Any Other Ascending Pathways Due to
    • Presence of accessory nuclei that modulate input (see below)
    • Bilateral representation of auditory impulses on each side

Efferent Cochlear Bundle

The CNS can influence its own sensory input to protect us in conditions of very loud noise and to enable us to “sharpen” our perceptions of auditory stimuli

  • Crossed and uncrossed fibers from the olivocochlear bundle project peripherally from the brainstem to the cochlea forming the efferent cochlear bundle
  • Suppresses auditory nerve activity by inhibiting the receptivity of the organ
  • Auditory sharpening – the processes whereby relay nuclei in the auditory pathways differentially inhibit impulses concerned with certain frequencies thereby enhancing the frequencies of other sounds

Auditory Cortex

Primary Cortex

  • areas 41 and 42 – mostly buried in the insula
  • Contains Heschel’s Gyri
  • Cortical auditory area receives geniculotemporal fibers from the MGN via the internal capsule
  • Each cochlea is represented bilaterally however, cortical response is greatest contralaterally.

Sound Localization

A 2-phase process

  • Convergence and comparison of auditory input from the 2 ears
  • Distribution of the analysis to the appropriate side of the system
  • Trapezoid body and Superior Olivary Nucleus are essential to localization

Association Cortex

  • Laterally specialized – with dominant hemisphere mainly concerned with processing speech and language and nondominant hemisphere concerned with nonverbal auditory stimuli

Brain Damage and Hearing Impairment

  • Destruction of the cochlea, cochlea nerve or cochlea nuclei (both dorsal and ventral) results in complete ipsilateral deafness
  • Damage to lateral lemniscus – bilateral partial deafness, greatest in contralateral ear
  • Complete cortical deafness is very rare, as it requires lesions affecting the transverse gyri of Heschel, bilateral
  • The clinical signs of damage to the auditory nerve are deafness and tinnitus
    • Conduction deafness – interference with passage of sound waves through the external or middle ear (e.g., wax build up in outer ear or otitis media) – deafness is never complete or total
    • Nerve deafness – results from damage to cochlear nerve or receptor cells

Common causes of deafness

  • Old people progressively lose hearing (Presbyacusis). High frequencies are lost first. Starts relatively early in life (during the twenties)
  • Otosclerosis – most common adult cause of hearing loss. Autosomal dominant genetic disorder Characterized by fusion of stapes to oval window causing difficulty of movement followed by eventual cessation of ear ossicle movement. It is amenable to surgery.
  • Persistent loud noises can cause cells to die (frequency dependent).
  • Infection Viruses e.g. mumps. German measles during pregnancy can cause complete destruction of cochlear nerve in fetus.
  • Middle ear infections e.g. Otitis media – bacterial infection causing swelling and outward bulging of tympanic membrane, pain and pus collection in middle ear. Most common in children as eustachian tubes are not fully formed and thus don’t drain well into nasopharynx.

Brain damage, aphasia, and agnosia

Sensory/receptive aphasia

  • inability to differentiate speech sounds
  • caused by lesions in superior temporal gyrus in the region adjacent to primary auditory cortex of dominant hemisphere

Word Deafness/sensory aphasia

  • person can hear what is said, but cannot interpret the words
  • lesions in Brodmann’s area 22 in dominant hemisphere

Auditory amnesic aphasia

  • inability to repeat series of words presented acoustically, although ability to repeat single words remains intact
  • lesions in middle temporal gyrus (further away from primary auditory projection areas)

Acoustic agnosia

  • inability to differentiate nonverbal speech sounds
  • right hemisphere lesions

Attention

SALIENT CHARACTERISTICS OF ATTENTION

  • Sequential process involving many brain systems
  • Limited capacity- engagement of system in one task can interfere with second task
  • Varies between and within individuals under different conditions (depression, fatigue, injury can all impact attention)

NEUROANATOMICAL SUBSTRATES

  • Inferior Parietal Cortex– spatial selective attention; hemineglect
  • Frontal Cortex– response selection; control; sustained attention; switching; searching
  • Orbital Frontal Region– response initiation; inhibition
  • Medial Frontal Lobe (paralimbic cingulate cortex)- intent to respond; consistency of responding; focused attention
  • Dorsolateral Frontal Cortex– sequencing; persistence; switching; focus
  • Limbic System– establishes salience, whereby determining priority of incoming stimuli; limits of attention (hippocampus- memory encoding and retrieval constrain attention)
  • Subcortical System– relay of sensory input through thalamus; caudate nucleus selection of motor responses, selection and coordination of sensory info
  • Midbrain System– arousal and activation

MODELS OF ATTENTION

Pibram & McGuiness (1975)

Based on animal research- Three essential factors

  • Arousal- “the primordial attention system”
    • orienting response to sensory input
    • system from spinal cord through brainstem reticular formation, with forebrain control exerted by amygdala and portions of frontal cortex
  • Activation
    • basal ganglia
  • Effort

Lezak

“Mental activity variables”: Efficiency of mental processes involved in cognitive functions, but do not have unique behavioral end product

  • Attention
  • Activity rate- speed of mental operations and motor responses
  • Consciousness- awareness of self and surroundings; level of arousal

Link between arousal and attention: disorder of arousal always involves disorder of attention; disorder of attention does not always involve disorder of arousal

Mesulam (2000)

  • (critics think model is too narrow)
  • Discusses matrix (confusional state) vs. vector (where you are focusing your attention)
  • Attentional Matrix (general state)
    • Domain-specific attentional processes: attentional processes to certain stimuli; visual neurons mediate visual attention to visual stimuli
    • Domain-independent attentional processes: “bottom up” influence of ascending reticular activating system and “top down’ influence of cerebral cortex (frontal lobe)
  • Bottom-up modulation– Ascending reticular activating system (ARAS)
    • reticulothalamocortical pathway- cortical arousal by passing sensory information through thalamus towards cortex
    • transmitter-specific extrathalamic pathways from brainstem and basal forebrain to cortex
    • Global influence on attention without selectivity for sensory modality or cognitive domain
  • Top-down modulation– parietal, limbic, prefrontal cortex (right hemi preference)
    • context, motivation, significance, volition
    • research: activation of prefrontal cortex and posterior parietal cortex common to almost all attentional tasks, regardless of modality or domain
    • frontal important in processing novel information
    • limbic important for mood and motivational factors
  • Top-down Modulation and Bottom-up Modulation impact Modality- and Domain-Specific Attentional Modulations (for sounds, tactile stim, colors, motion, words, spat targets, faces, objects, memories, etc.)

Posner & Peterson (1990)

Three major functions:

  • orienting to sensory events- involuntary process
  • detecting signals for focal processing- voluntary
  • maintaining vigilant or alert state

Two attentional systems:

  • Posterior attention system: orienting, awareness of environment; dorsal visual pathway; primary cortical connections to parietal lobe
  • Anterior attention system: signal detection; anterior cingulate gyrus, supplementary motor cortex

Disengage – posterior parietal region

  • Shift – superior colliculus
  • Engage – pulvinar of the thalamus

Mirsky (1996)

Factor analyzed neuropsych data for 5 factor solution

  1. Focus/execute
  • capacity to concentrate attentional resources and screen out distracting stimuli
  • tests require ability to identify salient task elements and perform motor responses under conditions of distraction (digit symbol, stroop, trails, letter cancellation)
  • focus- superior temporal and inferior parietal cortices; corpus striatum
  • execute- inferior parietal and corpus striatum
  1. Sustain
  • ability to stay on task in vigilant manner
  • tests require person to maintain attention over time (CPT)
  • rostral midbrain
  1. Shift
  • ability to change attentional focus from one aspect of stimulus to another in flexible, efficient manner
  • selective- maintain cognitive set in presence of distracting stimuli
  • divided- processing more than one set of information at a time
  • prefrontal, frontal association areas
  1. Encode
  • ability to hold info briefly in mind while performing mental operation on it
  • hippocampus, amygdala
  1. Stabilize
  • reliability of attentional effort
  • measures by Mirsky using variability in reaction time on CPT and commission errors
  • midline thalamic and brainstem structures

Problems

  • Critics think Mirsky’s model is too broad; overlap between attention and exec fx (encode vs working memory)
  • Also, he used factor analysis, so model highly dependent on tests used
  • Problem of shared method variance- uses same or highly related tests to measure functions

Cohen, Malloy, & Jenkins (1998)

Four components:

  1. Sensory selective attention
  • process by which sensory input is chosen for additional processing and focus
  • depends on filtering (selection of what is attended to occurs on basis of sensitivity; may attend to something novel; early stage of processing), focusing and selecting, and disengagement (attention remains on stimulus until another stimulus or internal event shifts attention)
  1. Attentional capacity and focus
  • focused attention- intensity and attentional resources devoted to task
  • influenced by “energetic factors”- arousal, motivation, effort
  • influenced by “structural factors”- memory, processing speed, cognitive ability
  1. Sustained attention
  • helps to maintain optimal performance over time
  • even “normal” people can have variations in attention (this distinguishes attention from other cognitive processes- visual-spatial skills always same)
  • highly dependent on task duration
  • also dependent on vigilance requirement (high demand for readiness for low-probability target); dependent on reinforcement and target:distracter ratio
  1. Response selection and control
  • facilitates action
  • controlled and effortful
  • exec fx strongly associated: intention, initiation, generative capacity, persistence, inhibition, switching

METHODOLICAL ISSUES IN ASSESSMENT OF ATTENTION

  • No pure test of attention
  • Attention primarily serves to facilitate other cognitive functions (memory, EF). Therefore, many tests load not only on attention, but also other domains.
  • Attention not a unitary process; can’t be assessed with only one test; use a multifactorial approach
  • Attentional performance usually derived from comparing performance across tasks that load on different cognitive functions.
  • Absolute performance provides less info than looking at performance inconsistencies.

Factors to consider in assessment

Test factors

  • spatial characteristics
  • temporal demands
  • memory demands
  • EF demands
  • processing speed
  • complexity
  • task salience, relevance, reward value

Patient factors

  • arousal
  • motivation
  • effort
  • anxiety
  • depression
  • fatigue
  • general cognitive ability

Type of attention

  • goal-directed activity: anterior
  • awareness of environment: posterior

Tests of Attention

Selective attention- cancellation tasks; spatial search tasks (computerized presentation of visual stimuli, evaluates time taken to scan visual array); spatial cue paradigms (neutral cue is presented at some spatial location prior to onset of target, on some trials, cue correctly signals future position of target, other times it doesn’t)

Response selection and control- go/ no-go and CPT (inhibit responses); Trail Making (response alternating and switching); CPT; Sorting tasks (failure to maintain response set; switching); Fluency measures (quantity of response output, initiation, persistence); Stroop (ability to inhibit a response)

Attentional capacity and focus- Digit Span; Arithmetic; PASAT; Symbol Digit Modalities; Digit Symbol; Corsi Blocks; Stroop; Sentence Repetition

Sustained attention and vigilance- CPT; cancellation tasks; symbol coding tasks (earlier vs later performance)

ATTENTIONAL IMPAIRMENT

  • Most common of all cognitive impairment
  • Inability to allocate resources to task at hand
  • Failure to perform at optimal level, despite intact cognitive ability
  • Inconsistency in performance

Mirksy’s Nosology of Disorders of Attention (presented at INS 2000)

  1. Familial/ Genetic
  • deficits in sustained attention among first degree relatives of schizophrenics
  • relatives of children with juvenile myoclonic epilepsy have similar deficits in visual and auditory attention
  • “epilepsy gene”- human lymphocytic antigens (HLA) region of chromosome 6p. Present in kids with JME and their relatives. This gene also implicated in schizo and ADHD. A form of inherited deafness also found on this gene, and Mirsky found that auditory CPTs more sensitive than visual versions among schizo, absence epilepsy, and JME. Tentatively suggests that all disorders share common genetic fault expressed as an impairment in sustained attention.
  1. Metabolic disorders
  • affect biochemistry and neurochemistry of body, can result in changes in brain structure and EEG
  • Uremia from end-stage kidney failure: deficits in sustained attention; EEG pattern similar to absence epilepsy; toxins associated with kidney failure “attack” centrecephalic brainstem structures implicated in absence epilepsy
  • Early-treated PKU: problems with attention, impulse control, distractibility, persistence; many receive ADHD dx
  1. Environmental factors
  • Poverty: associated malnutrition and infection
  • Maternal alcohol use and FAS
  • Pregnancy and birth complications
  • Lead exposure
  • Lack of intellectual stimulation
  1. Other factors
  • Cerebral insults: head injury, tumor, infection
  • Sleep and breathing disorders

DISORDERS OF ATTENTION

Acute Confusional State

Abrupt change in mental state, usually caused by toxic or metabolic disorder, environmental stressor, or multifocal brain disease (meningitis, encephalitis, TBI in acute phase)

Three primary features:

  • disturbance of vigilance; distractibility; impaired working memory
  • inability to maintain stream of thought
  • inability to carry out goal-directed movement

Clinical features

  • inattention with poor mental control
  • poor concentration and vigilance
  • distractibility
  • disorientation
  • other cog problems: arousal problems, memory loss, hallucinations
  • interferes with performance on tests of other cognitive abilities.

Neglect Syndrome

  • Disorder of spatial attention.
  • Right posterior parietal lesion
  • Spatial attention- two components
    • sensory-motor: translate visual-spatial info into body movements
    • cognitive: mental representation, planning strategies, volitionally shifting from a target
  • Behave as though left half of universe ceases to exist
  • “Probability of attracting attention, entering awareness, influencing cognitive processes or becoming target for action decreases in proportion to relative leftness of stimuli”
  • Can be multi-modal- rightward bias of auditory, somatosensory, and olfactory targets

ADHD

  • Disorder of sustained attention, behavioral inhibition, and executive function (Barkley)
  • Behavioral diagnosis
  • Barkley study looking at validity of measures in assessing ADHD symptoms- able to discriminate ADHD from normal children, but less consistent in discriminating ADHD from other clinical groups

TBI

  • Result from impact injury or shearing injury (damage subcortical white matter, result in arousal and activation deficits)
  • Changes in attention throughout recovery process
    • initial diminished alertness; later decreased response inhibition, slower reaction time
  • Common ongoing complaint even after recovery of most other functions
  • More pronounced deficits when younger age at injury
  • Compounded by EF deficits and slow processing speed

Sleep Apnea and Snoring

  • Apnea- deficits in attention and concentration; hyperactivity in kids; seem to be related to daytime sleepiness secondary to frequent nighttime arousals (other cognitive problems related to hypoxemia)
  • Snoring- also see attention problems due to daytime sleepiness

 

Apraxia

DEFINITION

  • Apraxia – derived from Greek word, praxis, meaning to do or action
  • An acquired disorder of skilled purposeful movement
  • purposeful important b/c may do automatically (e.g., can spontaneously brush crumbs off lap but can’t do so on command or intentionally)
  • Syndrome of higher motor dysfx
  • distinct from paresis in same way aphasia distinct from dysarthria
  • analogous to agnosia, a syndrome of higher sensory dysfx
  • NOT caused by paresis, abnormal tone or posture, akinesia, ataxia, sensory loss, inattention, poor comprehension or other cognitive problems (i.e., primary motor skills and comprehension ok)
  • In practice, term sometimes used as shorthand for ideomotor apraxia, most common type

HISTORY

  • Term introduced in 1870 by Steinthal, but prior to 1890 much confusion and not clearly differentiated from aphasia and agnosia
  • In 1900, Hugo Liepmann (one of Wernicke’s students) clearly established apraxia as distinct disorder; later provided classification of subtypes and theory of normal and abnormal actions (praxis)
  • Much debate since about definitions, etiology, etc.

LIEPMAN’S NEUROANATOMICAL MODEL

  • suggested that the left parietal area is critical for control of complex movement; mediated by the left frontal lobe and area 4 for the right side of the body; disruption anywhere in this system would produce right-sided apraxia
    • control of the left limbs was proposed to be mediated through cnxns from the left parietal area to the left frontal cortex and then to the right frontal cortex (via CC)
  • problems with this theory include:
    • does not recognize the involvement of the basal ganglia and thalamus in movement
    • although it is assumed that the posterior parietal and prefrontal regions are the primary regions involved in apraxia, patients w/circumscribed cortical lesions do not typically demonstrate chronic abnormalities on standard clinical tests of apraxia (emphasizes basal ganglia and thalamus’ role in apraxia)

MAIN SUBTYPES

3 Classic types defined by Leipmann

Limb-Kinetic Apraxia (aka, melokinetic or innervatory apraxia)

Leipman defined melokinetic as the loss of kinetic memories for a single limb; related to small lesions in motor cortex which are insufficient to produce paresis

  • Movements appropriate to intended action, but movements are clumsy, unskilled, or imprecise
  • Affects fine-motor movements, especially finger movements (gross motor ok)
  • More obvious when testing distal movements, and is especially evident when making rapid movements (like finger tapping)
  • Defect is unilateral, opposite to involved hemisphere
  • Least frequently dx, reflecting uncertainty about how differs from mild paresis or ataxia
  • Current definitions might consider this apraxia more of an ataxia

Testing

  • Simple manual acts troublesome (e.g., playing cards, picking up coin from table, buttoning shirt)
  • Problems on grooved pegboard, finger-tapping speed, etc.

Lesion Site

  • Limited lesions of contralateral premotor area or subjacent white matter

Ideomotor Apraxia

Ideomotor_Apraxia_Model

(Leipmann first called motor apraxia and then ideokinetic apraxia)

  • Defective execution of individual components of action
  • comprehension ok, motor system intact, and activity can be performed spontaneously
  • Separation exists between idea of an act and its performance (i.e., “disconnection b/t idea of movement from kinetic memory images)
  • See w/ both transitive (using tool/instrument) and intransitive (not involving tools/objects such as wave good-bye, cough) commands, although transitive typically more impaired
  • Refers to single action, not a sequential motor performance
  • Errors can improve upon imitation
  • Can be seen in oral (buccofacial), limb, or axial musculature
  • In contrast to limb-kinetic, typically see bilateral deficits (although can be unilateral)

Testing

  • Most notable when asked to pantomime actions to verbal commands
    • First test by “Show me….”
    • Then see if improves upon imitation
    • Then see if improves w/ use of actual object
  • Buccofacial (i.e., oral apraxia) ~ first described by Hughlings Jackson
    • Gesture: Kiss the air, repeat “Pa”
    • Imagined: Pretend to blow out a match, suck w/ a straw, cough
    • Real: blow out match, drink water thru straw
    • Common among Broca’s aphasics
  • Limb
    • Gesture: Salute, stop traffic, wave good-bye
    • Imagined: Pretend to use a comb, to write, use a screwdriver
    • Real: comb hair, write w/ pencil or pen
  • Axial
    • eyes look up; close your eyes; neck: bend head down; trunk: stand, kneel, walk backwards
    • may be mediated by different pathways since often preserved even in severe apraxia

Errors

  • Failure to generate response
  • Spatial: correct core movement, but limb movement thru space incorrect (e.g., sawing horizontally rather than vertically)
  • Perseveration: e.g., after blowing match, repeats for sucking straw
  • Verbalization is produced instead of action (saying “cough,” instead of coughing)
  • Use body part as part of object (using hand for comb)
  • Sequential: sequencing errors (demonstrating key use by rotating wrist, then extend arm)
  • Timing: Failure to coordinate speed w/ spatial aspects of gesture

Lesion site

  • Left-hemisphere dominance for praxis
  • Can occur w/ lesions anywhere w/in perisylvian region
  • Occurs after damage to one or more areas (Ansher and Benson, 1993)
    • Lesion to L par lobe can damage arcuate fasciculus, which interrupts flow of info anteriorly and prevents motor system from receiving direction to act (conduction aphasia often seen)
    • Large lesion to L premotor area interferes w/ motor execution (often seen w/ nonfluent aphasia and hemiparesis)
    • Lesion to anterior corpus callosum leads to apraxia; only seen w/ left hand (no aphasia)

Ideational Apraxia

  • Failure to perform a sequential motor movement, though each individual component can be performed in isolation (e.g., completed in the wrong order or perseverate on single step)
  • Fail at complex task because of faulty overall plan or “idea”
  • Component skills ok, but include wrong ones or in wrong order when completing sequence
  • In contrast to limb-kinetic, see bilateral deficits
  • Lots of conceptual confusion in definition of ideational apraxia; practical utility may be limited

Testing

  • Have pt perform series of component actions in correct order
  • Fold letter, insert in envelope, seal it, apply postage
  • Light candle: give box of matches and candle

Lesion site

  • Localization unsettled, but seen w/ both:
    • damage to left parietal lobe (large lesion)
    • most commonly occurs with diffuse cortical involvement from dementia
  • May represent primary disturbance of attention or executive fxs (Weintraub)

MECHANISMS UNDERLYING APRAXIA

Over the years, two general hypotheses proposed

Disconnection Hypothesis

  • First proposed by Leipmann and then vigorously defended by Geschwind
  • Disconnection of critical left cortical areas from zones of execution (see above under ideomotor); inability to elicit correct motor sequences in response to language
  • Discnxn b/t language areas and visuokinesthetic engrams
    • fibers either cross from (1) Wernicke’s area to the contralateral association area or (2) from the left premotor area to the premotor area on the right
  • lesions that destroy the left premotor cortex are often associated w/right hemiplegia, but if the patients were not hemiparetic, they would probably be apraxic on the right
    • lesions w/c disconnect the posterior language area from the motor association cortex (in the arcuate fasciculus) cause patients to be able to understand directions but not perform them
    • Does NOT explain why pts w/ such lesions can’t imitate gestures

Representational (or Praxicon) Hypothesis

  • Heilman argues for existence of “visuo-kinesthetic engrams” or “praxicons” in the inferior par. lobe
  • Based on idea that nervous system learns and stores skilled movements
    • Kimura has argued that this knowledge is stored in the dominant parietal lobe
    • A disconnection b/t the area that stores this info and the premotor/motor areas will result in poor implementation of skilled movements
  • When first learning skilled movement, basal ganglia and cerebellum play role, but later memories involve cortical representation – praxis represents motor equivalent of remote memories
  • Supported by fact that some apraxic pts lose ability to form movements, as well as ability to recognize correct movements in others

IDEOMOTOR APRAXIA MODEL

Model depicting possible impairments in ideomotor apraxia

  • Level B Lesion: Can’t recognize gestures because damage to representations of learned, skilled movements; gesture discrimination problem
  • Level C Lesion: Bilateral ideomotor apraxia but can comprehend and discriminate gestures; movement memories not destroyed, just can’t interact w/ anterior areas responsible for motor implementation
  • Level D Lesion: Bilateral ideomotor apraxia but can comprehend and discriminate gestures; innervatory patterns can’t gain access to motor area

DIFFERENTIAL DIAGNOSTIC ISSUES

  • Disorders of basal ganglia and cerebellum may be associated w/ nonapraxic movement disorders such as postural change, tone, tremor, etc.
  • Aphasia
    • Many apraxic patients are also aphasic (b/c of lesions near or overlapping speech centers), so must be distinguished
    • If pt performs poorly when required to indicate with limb, but performs okay when required to provide a yes/no answer, they may be apraxic
  • tend to occur in clusters of disabilities that share a common anatomical pattern
    • g., apraxias of impaired ability to perform skilled tasks on command or imitatively or to use objects are commonly associated with language deficits (b/c of lesions near or overlapping speech centers)
    • g., facial apraxia and deficits in expressive speech (Broca’s aphasia); anatomical regions for verbal expression and facial movement are close
    • anosognosia – frequently have right-hemiparesis and may attribute clumsiness to the use of their non-dominant hand

TERMINOLOGY CLARIFICATION

Many neurobehavioral syndromes with some motor dysfx have been termed “apraxia” but likely not really apraxia as traditionally defined

Constructional apraxia

(Kleist; also associated with Hecaen)

  • Problem with drawing, assembling, or building
  • Bears no relation to Liepmann’s definition of apraxia, thus “visuoconstructive impairment” might be better term
  • Can be tested by paper and pencil (copy drawing; draw house, clock, etc), three-dimensional construction
  • Traditionally thought to be caused by parietal lesions (either left or right)

Dressing apraxia

  • difficulty with dressing (follows rt hemi lesions)
  • Also bears little relation to original apraxia definitions (e.g., no dissociation b/t voluntary-automatic and performance on command )
  • Perhaps most frequent in dementia or confusional states
  • Caused by any number of lesions, including left-sided neglect, Balint’s syndrome (simultanagnosia or optic ataxia)
  • NOT seen in isolation

Ocular apraxia

Oculomotor apraxia or psychic paralysis of gaze

  • Inability to perform purposeful ocular movements
  • component of Balint’s syndrome
  • deficit in visual scanning; inability to shift gaze at will toward new visual stimuli and inability to maintain fixation on an object
  • Almost always accompanied by either optic ataxia or visual disorientation

Optic apraxia/Optic Ataxia

  • Apraxia of ocular searching movements affecting visually guided hand movement
  • Usually results from bilateral posterior parietal lesions
  • Sxs same for optic apraxia/optic ataxia – different terms vary in emphasis on underlying neurobehavioral deficits that accounts for phenomenon
  • Seen in Balint’s syndrome

Gait apraxia

  • d/o of gait seen in diseases affecting frontal lobe
  • First and most prominent sx of Normal Pressure Hydrocephalus
  • Seen when pts fail to alternate leg movements, don’t shift weight forward, pick up same leg twice in row; foot can be “magnetized” to floor
  • Most pronounced when starting to walk
  • Stepping reflex preserved so might step over obstacle spontaneously

Verbal apraxia (aphemia)

  • used by speech pathologists to describe pxs w/ speech fluency or dysarthria

Apraxia of speech

  • an articulation d/o resulting from brain damage
  • impairment in capacity to program positioning of speech musculature and sequencing of muscle mvmts
  • not a language/aphasia problem
  • in contrast to dysarthria, practice worsens condition
  • inconsistent articulation errors; pts sounds like they are struggling to articulate words

Callosal apraxia (aka, unilateral apraxia)

  • form of ideomotor apraxia ass’d w/ difficulty in executing motor sequencing tasks of the left hand following lesions of the CC
  • thought to result from disconnection of the visuokinetic motor engrams of the left hemisphere from the motor area of the right
  • seen in lesions affecting fibers passing through the anterior CC

Conceptual Apraxia

  • an inability to perform limb movements on command resulting from impairment in linking the meaning or intent of an action to movement plan
  • movements are well performed but inaccurate in content

Frontal apraxia

  • An inability to perform routine actions because of temporal or sequential disorganization
  • Verbal mediation does not improve performance

Links between goal of action and specific acts that must be “assembled” to serve goal become destabilized and action sequence becomes a series of isolated fragments

Aphasia Syndromes Summary

Aphasia Syndromes Summary

  Speech Auditory Comprehension Repeating Naming
Broca’s . Normal . .
Wernicke’s Fluent . . .
Conduction Fluent Normal . — . –
Global . . . .
Anomic . Normal Normal .

KEY:

= minor impairment

= significant impairment

= severe impairment

Anoxia

  • The brain accounts for 2% of a person’s total body weight, but it consumes 20%-25% of the total oxygen inspired
  • While other organs can withstand deprivations of oxygen for extended periods of time, the brain can be effected by even subtle deprivations
  • If anoxia continues for more than a few minutes, an anoxic/ischemic encephalopathy will likely result, frequently involving both neuropsychological impairments, neuroradiological abnormalities, and neurobehavioral effects
  • Oxygen is breathed in through the lungs and diffused into the pulmonary arterial blood. It gets metabolized with glucose in the cells to form carbon dioxide, which is removed from the cells by the venous circulation.
  • The heart delivers oxygenated blood to the organs (specifically, it gets delivered to the brain via the internal carotids and the vertebral arteries)
  • Cognition begins to be affected at 75% arterial oxygen
  • Unconsciousness occurs at about 50% arterial oxygen
  • Death occurs at 30-40% arterial oxygen
  • Watershed areas are most affected (hippocampus, basal ganglia, cerebellum, occipital cortex, and some frontal regions)
  • Neuropsychological deficits following anoxia/hypoxia include impaired memory, executive dysfunction, apperceptive agnosia (problem with visual synthesis of objects), visual-spatial deficits, and overall cognitive decline
  • Affective changes may arise following hypoxia due to injury to the structures of the medial temporal and frontal lobes

Anosagnosia

Tardive Dyskinesia

  • Some suggest that over ½ TD pts unaware of their movement disorder (have been larger prevalence rates: 88%)
  • Some suggests that unawareness of TD might be due to primary illness (SZ>BP for unaware).
  • Some suggest they’re denying the disorder /hiding it (thumb in clenched fist; tongue against top/ bottom teeth)
  • Expect OF>LT (unaware) but research has found exact opposite
  • Research has also shown double-dissociation of awareness (e.g., can be aware of one but not other)
  • Hypotheses
    • TD patients that are unaware are more globally and cognitively impaired.
    • neuroleptics may damage mesolimbic/ mesocortical dopaminergic projections and thus may produce an iatrogenic “frontal lobe syndrome.”

Sensory-visual denial

Hemiplegia

  • minimize the extent of damage often in a jocular fashion (anosodiaphoria).
  • think limb does not belong to them or even attribute them to another person (somatoparphrenia); O. Sachs
  • overestimate the strength of an unaffected limb (anosognosic overestimation)
  • false belief that the limb is moving (kinesthetic hallucinations).
  • separate limb has appeared on another part of the body (phantom supernumerary limb).
  • These strange phenomena do not necessarily appear with hemiplegia.
    • studies have shown that anosognosia for hemiplegia associated with higher co-occurrence of confabulation
    • anosognosia more common for L side of body (RBD)

Hemianopia/ Anton’s Syndrome

  • great example (unaware of cortical blindness, & confabulatory)
  • can also see unawareness of visual field cuts (hemianopsia)
  • Hier et al. found that anososgnosia for hemianopsia & paresis associated with:
    • larger lesions
    • more severe hemiparesis
    • P lobes and surrounding tissue damage

Neglect

  • Unilateral neglect can occur from L or RBD (R>L)
  • damage to RH associated with:
    • greater impairment
    • longer lasting
    • anosognosia more likely
  • have demonstrated d.dissoc of neglect from other somato-sensory, motor, and visual field cuts (suggesting):
    • can’t infer causality of the existence of anosognosia of limb paralysis in relation to s-s disorders
    • anosog for L hemiplegia isn’t just a manifestation of inattn to the L side of egocentric space (b/c d.d)
    • unawareness of hemiplegia and neglect are functionally unrelated and if co-occurrence results, it is due to anatomical contiguity, not causality.
    • anosognosia is dissociable into function-specific forms. Anosognosia is not secured by some superordinate organ in the nervous system, but is decentralized into functional, specific blocks.

Amnesic Syndromes

MTL damage & thalamic damage not associated with anosognosia

  • H.M.
  • transient global amnesia
  • TLE (no difference btwn R/L- Seidenberg; aware of cogt impairments in relation to relatives reports)
  • A. (Squire’s pt)- thalamic damage: “My memory is like a filing cabinet…The problem is that I cannot find something when I want to” (p.385).

Diencephalic/ F lobe damage (do see anosognosi)

  • AD insight relatively intact early in disease course, but with greater F involvement, see poor insight
  • KD often present with anosognosia and confabulatory beh

Aphasia

  • BA (painfully aware of deficits)
  • WA often unaware of paraphasias/ receptive speech impairment. Lebrun stated this on grounds that:
    • many of these individuals are talkative- if aware, wouldn’t talk b/c of errors
    • often don’t refrain from speaking
  • dissoc of aphasic errors has been demonstrated:
    • WA (fluent), reading/ writing ok
    • self-corrected her phonemic paraphasic errors while ignoring her semantic errors.
    • different mechanisms might underlie the monitoring of these errors

THEORIES OF ANOSOGNOSIA

Neuroanatomically-based theories

Focal lesions

  • most agree that anosognosia results from R or bilateral damage
    • some WADA studies have suggested greater unawareness of hemiplegia following RH anethesia compared to LH; although Loring’s group didn’t find this (found that 82% unaware regardless of H)
  • Geschwind (1965) proposed a disconnection theory of anosognosia.
    • RHD>LHD to produce disturbed awareness; b/c RH normal poor linkage to speech areas assoc with LH is further weakened by RHD
    • confab is LH attempt to explain what pt can’t comprehend
    • pblms with theory (Bisiach et al.):
      • pts with telencephalic commissurotomies needn’t show misrepresentation of objects/ events in L side of personal/ xtrapersonal space which often happens following specific type of RBD
      • if info relative to the specific disorder is unable to be conveyed through the speech area, then nonverbal expression should be intact in these unaware patients, which it is not.
      • Often see cognitive disorders in nonverbal behavior but verbally acknowledge their illness. (e.g., pt admits their hemiplegia but still tries to walk or knit).
      • (mine)- see d.dissoc (theory can’t account for this)
    • Bisiach et al. : domain-specificity of anosognosia (not superordinate, monolithic monitoring system).
      • pts who are blind due to peripheral lesions are aware of their deficits and behave like a blind person.
      • pts with central lesions have an associated “visuo-specific cog impairment –> monitoring deficit.
      • model defines two breakdowns in the monitoring mechanism of cortical blindness.
        • failure of the “sensory transducer” which transmits impulses from the retina to the brain.
        • failure of the “sensory processor” which mediates the action between the transducer and the neural regions responsible for the cognitive processing of visual input

Diffuse damage

Little support for this (can see anosognosia but cog intact)

Motivation Theories

  • psych d. mech of denial (Weinstein & Kahn)
  • one’s premorbid personality (precursor for dev)
    • considerably insecure
    • strong drive for perfection and superiority.
    • Illness viewed as imperfection.
    • euphoric patients were once compulsive, meticulous and worrisome pre-insult.
    • “drive to self-actualization” & to be “well” is the motivating factor behind its dev
  • pblms with psychodynamic account:
    • dissoc (can’t account for)
    • anososog can dev after illness has been there for awhile (case study of paraplegic pt, suffered another stroke, became unaware of paralysis)
    • not lasting phenomenon (often subsides over time)- theory doesn’t account for this

Dissociable Interactions and Conscious Experience (DICE)

  • Schacter & McGlynn model conscious awareness system (CAS)
    • conscious experience of remembering, knowing, perceiving, comprehending…requires activation of specific/ distinct system which interacts with modular systems concerned with specific fx (receptive lang)
    • CAS input received from ouput of these cog fx
    • Low activation of normally highly active system would result in no input into CAS & thus anosog

Model allows for domain specificity, involves both P and F lobes (P= CAS, output link to F= ex system involved with initiating, organization, monitoring)

Alexia

DEFINITION

  • Alexia is an acquired deficit in the ability to interpret written language; does not refer to those impairments (congenital or acquired early in life) which prevent the normal acquisition of reading skills (which are considered developmental dyslexia or simply dyslexia)

HISTORY

  • Recognized for centuries, but became a significant problem only in 20th century, when literacy expectations increased considerably
  • Origin of current concept of alexia stems from two case reports by Dejerine (1891, 1892); cases represent what has become known as central alexia and posterior alexia
  • Dejerine’s alexia classification fell out of use until repopularized by Geschwind (1962)

MAJOR SYNDROMES (3 types)

Central Alexia (Alexia with Agraphia)

  • Basic clinical features:
    • severe (not necessarily total) disturbance of both reading and writing
    • preserved ability to copy written language, but in slavish and non-comprehended manner
    • loss of ability to name letters, to comprehend spelled words, or to read out loud
  • Often accompanied by other neurobehavioral disorders including:
    • aphasia
    • components of Gerstmann Syndrome (finger agnosia, right-left confusion, acalculia, and agraphia)
    • some degree of hemisensory loss and/or right homonymous visual field defict
  • Locus of pathology includes inferior parietal lobe of language dominant hemisphere, centering on angular gyrus; typically damage to both cortex and white matter
  • Causes most often from occlusion of MCA or distal branches (inferior parietal lobe); may also be caused by neoplastic lesions
  • Other common names: semantic alexia, parieto-temporal alexia, total (literal and verbal) alexia, letter and word blindness, surface alexia

Posterior Alexia (Alexia without Agraphia)

  • Basic clinical features:
    • Individual can comprehend written material
    • Writing is almost or totally w/in normal limits BUT can’t comprehend what write
    • Easily write but have more trouble copying written language
  • With practice, can learn to read most letters out loud; words can then be spelled out loud and recognized auditorially
  • In most cases, ass’d neuro findings include:
    • right homonymous hemianopia
    • color naming disturbance
  • Pathology is typically infarction of left posterior artery territory, including splenium of CC (spares angular gyrus)
  • Disconnects visual info from language cortex
  • Other common names: verbal alexia, visual alexia, pure alexia, occipital alexia, associative alexia

Anterior Alexia (Frontal Alexia)

  • More recently discovered so also known as the “Third Alexia”
  • Basic clinical features:
    • Great difficulty naming individual letters of alphabet but can recognize some written words
    • Severe agraphia; ability to copy written language poor
    • Comprehend some spelled words, but poor at spelling aloud
    • Recognize some semantically meaningful words but fail to comprehend the grammatically significant function words – Agrammatism of written language
  • Accompanying neuro findings:
    • Right hemiplegia
    • Nonfluent aphasia
    • May include unitlateral sensory and/or visual-field neglect
  • Pathology is typically left frontal area
  • Other common names: literal alexia, letter blindness

Table Summary of Three Major Syndromes

  POSTERIOR CENTRAL ANTERIOR
Written Language      
Reading Verbal alexia Total alexia Literal alexia
Writing to dictation No agraphia Severe agraphia Severe Agraphia
Copying Slavish Slavish Poor, clumsy, omissions
Letter naming Relatively ok Severe letter anomia Severe letter anomia
Comp. of spelled words Good Failed Some success
Spelling aloud Good Failed Poor
Associated Findings      
Language output Normal Fluent aphasia Nonfluent aphasia
Motor No paresis Mild paresis Hemiplegia
Motor apraxia None Sometimes Frequently present
Sensation No problems Often sensory loss Mild sensory loss
Visual Fields Right hemianopia Sometimes hemianopia Usually ok
Gerstmann syndrome Absent Frequent Absent

TERMINOLOGICAL CLARIFICATION

Note that lots of other subtypes of acquired reading disorders have been suggested

THREE LINGUISTIC SUBTYPES: subtypes based on categorization of modern linguistics

Phonological alexia (dyslexia)

  • an inability to make spelling-to-sound correspondence rules
  • results in visual paralexias; real words misread as visually similar words (“cat” for “car”)
  • better reading of high frequency words
  • spelling usually impaired

Surface alexia (dyslexia)

  • grapheme-to-phoneme conversion disorder
  • can’t read words with irregular orthography (e.g., “tough” read as “tug”)
  • can read words with regular orthography

Deep alexia (dyslexia)

  • prime feature of this disorder are reading errors based on semantic (real word) substitutions for target words (semantic paralexia)
  • substituted word may be a semantic paralexia, a totally incorrect word, or neologism (“infant” could be read as “baby” “basement” or “garvon”)
  • Syntactic (functional) words are almost totally omitted
  • Pseudo words can’t be produced

OTHER ALEXIA TERMS

Global Alexia

  • term used to indicate total loss of the ability to understand written or printed language
  • synonymous with central alexia but indicates a total loss

Hemi-Alexia

  • individual can read adequately in one visual field but not in other
  • often seen when posterior CC is severed but both visual sensory areas remain intact

Hemi-Spatial Alexia

  • denotes a reading d/o where only half of word is read
  • seen in context of either a homonymous visual field or unilateral attention deficit (e.g., “basketball” read as “ball”)

Literal Alexia

  • inability to recognize letters of alphabet
  • significant feature of Anterior Alexia
  • often contrasted with verbal alexia

Verbal Alexia

  • opposite of Literal Alexia
  • can read individual letters but can’t read full word
  • seen in context of Posterior Alexia syndrome

Paralexia

  • substitutions made when reading aloud
  • multiple types: literal, semantic, phonemic, etc.

Spatial alexia

  • disorder of reading based on difficulty perceiving location (place holding) of letters or words or maintaining the correct sequence of lines of print
  • generally seen in context of right hemisphere dysfunction

Attentional dyslexia

  • reading disorder characterized by gross disturbance in reading multiple words or text, secondary to disturbance in visual attention; single-word reading relatively preserved

Central dyslexias

  • contrasted w/ peripheral dyslexias (below)
  • disorder that affects processes by which word forms activate meaning or speech production mechanisms (“higher” language processes)
  • Includes deep, phonologic, and surface dyslexias

Peripheral dyslexias

  • term suggested by Shallice and Warrington (1980), contrasted w/ ‘central dyslexias’
  • disorder caused by visual processing deficits in which visual inputs can’t be ass’d w/ stored representations of written words, includes attentional and neglect dyslexias and alexia without agraphia

Agraphia

DEFINITION

  • Agraphia – an acquired deficit in the ability to produce written language
  • Commonly used interchangeably with dysgraphia

HISTORY

  • Term first employed by Ogle (1867) to describe pt who could speak but not write
  • Since then, numerous classification systems have been proposed, but none universally accepted
  • Two general nosologies:
    • 1 longstanding tradition in context of clinical neurology; agraphias classified based on presence or absence of accompanying sxs such as aphasia, apraxia, visuospatial disorders
    • 1 more recent scheme from cognitive neuropsych perspective

CLINICAL NEUROLOGY CLASSIFICATION

Aphasic Agraphias

  • Fluent agraphias (ass’d w/ Wernicke’s, conduction aphasia, etc.)
    • Easily produce writing of normal quantity and length, but…
    • Paragraphic errors and lack of substantive words
  • Nonfluent agraphias (ass’d w/ Broca’s, transcortical motor aphasia, etc.)
    • Effortful, sparse production of written output
    • Writing usually large and messy
    • Prefer print, not writing
    • Spelling errors due to letter omissions (in contrast to the omission of function words seen in aphasia)
  • Alexia w/ agraphia
    • results from lesion of inferior parietal lobe
  • Gerstmann syndrome w/ agraphia
    • similar to fluent agraphias
    • Confusional state agraphia
    • Pure agraphia
    • writing deficit in absence of other aphasic sxs

Nonaphasic Agraphias

  • Apraxic agraphias
    • results from inability to correctly form letters
  • Motor agraphia
    • paretic agraphia
    • micrographia
    • agraphia w/ chorea
    • agraphia w/ tremor
    • writer’s cramp
  • Callosal agraphia
    • results from damage to CC and see unilateral agraphia
  • Reiterative agraphia
    • abnormal repetition of phrases, words, letters, etc.
    • often seen w/ frontal lobe dementia
  • Visuospatial agraphia
  • Hysterical agraphia

COGNITIVE NEUROPSYCHOLOGY CLASSIFICATION

Phonological agraphia

  • Syndrome that reflects impairment of nonlexical spelling route; impairment of sound-to-letter correspondences
  • Pathway employs “sounding out” words
  • Markedly impaired spelling of nonwords and unfamiliar words
  • Can spell words with w/ which they are familiar, even if complex or irregular

Lexical agraphia

  • Selective impairment of lexical (whole-word) spelling route that results in overreliance on spelling by sound-to-letter correspondence
  • Pathway employs whole-word, visual image route; essential for spelling irregular words
  • Inability to spell irregular words
  • Rely on phonological route (so, “feign” becomes “fane”)

OTHER AGRAPHIA TERMS

Agraphia Spelling Disorders

  • Deep agraphia
    • syndrome similar to phonological agraphia in that there is impairment of nonlexical spelling route so that nonwords and unfamiliar words are misspelled
    • also damage to lexical spelling route, resulting in semantic errors when writing
  • Surface agraphia
    • spelling d/o in which sublexical spelling-to-sound correspondences are used to assemble the spelling of the word
    • words may be phonetically plausible but misspelled
    • reverse phenomenon is phonological agraphia
  • Jargon agraphia
    • agraphia characterized by senseless combinations of letters or words
  • Semantic agraphia
    • loss of ability to incorporate meaning into spelling and writing
    • semantically incorrect but correctly spelled dictated homophones (eg, doe for dough) may be written
    • irregular words and nonwords are written correctly, however, demonstrating intact lexical and phoneme-to-grapheme conversion

Agraphia Writing disorders

  • Allographic agraphia
    • writing impairment ass’d w/ poor written production characterized by frequent omission errors w/ well-formed letter production
    • although well formed, letter production may reflect wrong letter
    • copying and oral spelling are spared
  • Spatial agraphia
    • writing impairment due to spatial deficits that affect nonlinguistic aspects of writing
    • term applied to wide variety of phenomena such as writing on slant, uneven spacing of letters or words and blank spaces, ignoring left side of page, writing over other words, etc.

Agnosia

DEFINITION

  • Agnosia: From Greek word, gnosis, or knowledge, so means absence of knowledge
  • Fundamentally defined as a disorder of recognition; inability to recognize the meaning of info conveyed w/in a given sensory system from external environment to the brain
  • Crucial feature is that it exists only in single sensory modality
  • NOT attributable to elementary sensory defects, mental deterioration, nonfamiliarity, aphasic misnaming of the thing or impaired consciousness or attention

HISTORY

  • Visual agnosia also called “mind blindness” (by Lissauer) or “psychic blindness” (i.e., seelenblindheit – Munk) – first demonstrated in a dog by Munk in 1881; “imperception” by Jackson
  • Term “agnosia” originally coined by Freud (1891)
  • Over years, lots of debate and confusion
    • “More mechanisms proposed for visual agnosia than number of reported cases”
    • Some folks argue agnosia is simply a combination of primary sensory loss and cognitive deterioration
  • One of the basic questions is whether agnosia is a sensory/perceptual or memory related disturbance
    • Proponents of both sides assume that two processes separable
    • Memory (Teuber): impairment of access to memory “located” at the interface between perception and memories
    • Sensory/Perceptual: (e.g., Bender) Agnosia is a perceptual impairment or the result of dementia
  • The most lasting distinction was proposed by Lissauer (1890), who differentiated apperceptive from associative agnosias

TYPES OF AGNOSIA

  • General distinction
    • Apperceptive: damage fairly early on in recognition assembly line, before perception is properly constructed; pts do not perceive objects normally so can’t recognize them
    • Associative: fault in later stages of recognition; perception may be ok, but access to memory or meaning not; Teuber – “a normal percept stripped of its meaning”
  • Classic distinction is that pts who can successfully copy but not identify are associative agnosics
    • probably not accurate since pts w/ severe deficits in visual perception can accurately copy things thru slavish, line-by-line approach

VISUAL AGNOSIAS (and related disorders)

Re: if patient can indicate recognition by verbal description or gesture, it’s an anomic disorder rather than agnosia

Apperceptive Visual Agnosia

  • Rare d/o in which pt has difficulty recognizing objects because of failure to perceive them
  • Commonly say vision is “blurred” or “foggy”; can’t describe what they see – but elementary sensory functions are relatively intact
  • Distinct from cortical blindness cuz intact visual acuity, but forms and shapes not recognized
  • Many pts recovering from cortical blindness
    • often seen with patchy visual field defects
  • Unable to draw misidentified objects or match them to sample
  • Lesions: typically bilateral damage to lateral parts of occipital
    • ass’d w/ path processes such as CM poisoning, mercury, cardiac arrest, bilateral strokes, basilar artery occlusion, or bilateral posterior cortical atrophy

Associative Visual Agnosia

  • Defect in recognizing visual stimuli that are well perceived (recent research suggests that these pts actually do have abnormal perceptual abilities, which has led to growing discontent w/ apperceptive-associative distinction)
  • Defect occurs beyond early stages of perception but before the stage of multimodal memory activity on which recognition depends (Damasio et al., 2000)
  • Particular difficulty in arriving at meaning of stimuli
  • Again, impairment of visual recognition is present, but visual acuity clearly good
  • CAN make drawings of pictures they can’t recognize and CAN match drawings/pictures to samples (although cannot put into categories)
  • Lesions: typically bilateral occipitotemporal lesions – from strokes in PCA
  • Commonly ass’d w/ right homonymous hemianopia

Visual Object Agnosia (ventral association processing disruption)

  • Specific inability to recognize, name, or demonstrate use of object such as pencil, chair, or clock
  • General visual object agnosics have an inability to recognize even the generic classes to which objects belong (as opposed to category-specific problems); don’t know face is face or car is car
  • Sometimes if object is moved or rotated can recognize (“static visual agnosia”)
  • Lesions: depend on either left unilateral or bilateral occipitotemporal (lingual, fusiform, and parahippocampal gyri), and infarction in cortex and underlying white matter of these areas
  • Optic Aphasia: visually presented objects can be recognized but not named, and auditory and tactile naming ok
    • Some folks think just milder form of visual object agnosia
    • Others think it’s separate entity

Prosopagnosia (ventral association processing disruption)

  • Inability to recognize previously known faces and failure to learn new ones
  • Generally know eyes, nose, mouth, etc., just can’t recognize particular face
  • NOT limited to human faces; farmer won’t recognize cows individually
  • Can recognize objects in environment as long as don’t require recognition of specific object w/in grp
  • Thus, can perform generic recognition but not specific recognition (car’s manufacturer)
  • Lesions: typically bilateral lesions of occipitotemporal cortex and underlying white matter; if unilateral, results from right hemisphere lesion

Color Agnosia – 3 classes

  • Central Achromatopsia (loss of color vision due to CNS disease)
    • Pts complain of gray or washed out look in affected area
    • Can be complete or just certain quadrants
    • Still perceive form and shape ok
    • Full-field ass’d w/ visual agnosia, especially prosopagnosia
    • Lesion: damage of visual ass’n cortex or subjacent white matter
  • Color Anomia (pt will succeed on visual-visual tasks and on verbal-verbal tasks, but cannot name colors)
    • pts have right-homonymous hemianopia and intact color perception of left field
    • other common correlate is pure alexia
    • lesion is usually in left hemisphere, mesially, in transition btwn occipital and temporal lobes
  • Specific Color Aphasia
    • Pt can sort colors and match them
    • seen in context of aphasia; represents disproportionate difficulty in naming colors
    • suspect left parietal damage

Simultanagnosia

  • Deficit characterized by failure to synthesize all elements of a picture or scene, even though components can be recognized in isolation
  • Often considered a variant of apperceptive agnosia
  • Varieties:
    • “Dorsal”(bilateral occipitoparietal lesions): pt can’t see more than one object at time
    • “Ventral” (left inferior occipital lesions): pt may be able to “see” more than one object at time

Balint’s syndrome

Caused by large bilateral parietal lesions – especially severe if frontal lobes affected. Clinical Triad:

  • Simultanagnosia
  • Ocular apraxia: an inability to shift gaze voluntarily from a fixation point; pts behave as though mesmerized by original object; gaze may be shifted if close eyes
  • Optic ataxia: impairment of visually guided movements as a result of a defect in stereopsis (depth perception); pts may not be able to read in methodical visual sweeps
    • Inability to manually respond to visual objects

Cortical Blindness and Anton’s Syndrome

  • Vision obliterated completely
  • Lesion: severe bilateral damage to visual cortices and to optic radiations
  • When accompanied by denial of blindness = Anton’s syndrome, form of anosognosia
    • may be caused by blindsight, where pt can see some movement but denies it; mediated by “second visual system” of superior colliculus, pulvinar, and parietal cortex
    • may also relate to impaired memory or insight because of ass’d temporal or frontal damage

Metamorphopsia

  • Very rare d/o where objects can be identified but they look odd; can appear fragmented, compressed, tilted
  • Macropsia: objects seen as larger than they are
  • Micropsia: objects smaller than they are

AUDITORY AGNOSIAS (and related disorders)

  • Impairment in ability to recognize speech or nonverbal sounds in presence of adequate hearing
  • Damage typically centers on temporal lobes
  • Severe damage results in cortical deafness
  • Lissauer’s apperceptive/associative distinction has been suggested but clinical differentiation problematic and no established anatomical correlates (Mesulam, 2000)
  • May reflect disconnection of unimodal auditory areas specialized for encoding the auditory properties of familiar objects from transmodal nodes that coordinate multimodal recognition

Pure word deafness (auditory word agnosia)

  • In the face of intact hearing and comprehension of nonverbal sounds, impaired recognition of speech
  • Voices are heard, but words do not make sense – may complain muffled, sounds like foreign language
  • Can’t repeat
  • May evolve from Wernicke’s aphasia, but spontaneous speech, reading, writing all intact
  • In aphasias, word sounds are perceived normally but they can’t link sound to meaning
  • Lesions: thought to reflect disconnection of primary auditory area on both sides from Wernicke’s area
  • may be bilateral or unilateral left temporal; CVA is most common cause

Auditory Sound Agnosia

  • Nonverbal counterpart of pure word deafness
  • Involves deficits in recognizing environmental sounds such as bell ringing, dog barking
  • Lesion: appears to be right hemisphere analog to pure word deafness

Phonagnosia

  • Reflects inability to recognize familiar voices
  • Auditory analog of prosopagnosia

Cortical Deafness

  • applied to pts whose daily activities and auditory behavior indicate an extreme lack of awareness of auditory stimuli of any kind and whose audiometric tone very abnormal
  • Most commonly seen in bilateral CV disease
  • Lesion: bilateral destruction of auditory radiations or primary auditory cortex
  • Distinguishing between auditory agnosia and cortical deafness is problematic

Receptive Amusia (sensory amusia)

  • loss of the ability to appreciate various characteristics of heard music
  • Occurs to some extent in all cases of auditory sound agnosia and in majority of pure word deafness
  • tough to study given the extreme variability in premorbid experience, skill, etc.

Auditory affective agnosia

  • pts show impaired comprehension of prosody • ass’d w/ right temporoparietal lesions and neglect

TACTILE AGNOSIAS (and related disorders)

  • Impairment of ability to recognize objects by palpation in hand
  • Because of complexity of somatosensory system, enormous variability in presentation of pts
  • Lesion localization two views:
    • ass’d w/ contralateral primary somatosensory area in postcentral gyrus
    • more diffuse aspects of cortex (eg, posterior parietal lobe) are involved in perception

Apperceptive Variety

  • Equivalent to astereognosis
  • Impaired ability to discriminate objects based on physical characteristics of size, weight, shape, density, or textural cues
  • inability to id objects by touch
    • Operationally defined in many ways, the most common being the loss of tactile object recognition in the absence of hypesthesia
    • Usually unilateral
  • deficit in tactile recognition in basic somatosensory perception
  • Often seen with agraphesthesia, impairment in recognition of characters on skin of palm
  • Lesion: contralateral primary sensory cortex

Associative Variety

  • d/o of tactile recognition in absence of primary somatosensory dysfx
  • More subtle than astereognosis
  • Like pts w/ associative agnosia, can’t recognize object in hand, BUT can accurately draw the object even when palpation fails to elicit recognition
  • Lesion: inferior parietal cortex, where high-level tactile processing occurs

Other Tactile Agnosias

  • Amorphognosia: Impaired recognition of size and shape of objects
  • Ahylognosia: Impaired discrimination of distinctive qualities of objects such as density, weight, texture, thermal properties
  • Tactile asymboly: Impaired tactile recognition of identity of objects in absence of amorphognosia or ahylognosia

THEORETICAL PERSPECTIVES

Stage Models

  • cortex builds up percept from elementary sensory perceptions
  • recognition achieved when resulting percept matched to stored info about object
  • Lissauer’s model of apperception and association agnosias is example
  • Validity called into question, since perception is not normal in many “associative” agnosias

Lissauer’s two-stage model of perception/recognition:

  • After an elementary Sensation occurs…
  1. there is an Object Perception (apperception), in which there is a conscious perception of a form, object, or “thing”,
  2. then there is Object Recognition (association), in which there is recognition of the category or identity of this “thing”…
  • …which allows for Naming, the retrieval of the word for the category or identity for the “thing”.

Disconnection Models

  • Most associated w/ Geschwind who suggested that agnosia results from disconnection btwn visual and verbal processes
  • Eg, Pts who fail to identify objects, who later used or interacted normally with the object
  • Disconnection theory can’t, by self, account for fact that most agnosics show abnormal verbal and nonverbal processing of viewed objects

Computational Models

  • Begins by trying to explain normal perceptual phenomena
  • Recognizes the enormous complexity involved in perceptual analysis and concludes that brain must store representations in some kind of codable, symbolic form that is flexible enough to accommodate perceptual variations required in everyday recognition
  • In this model, agnosia is a d/o dependent on perceptual dysfx
  • Marr’s Model of 3 types of representation
    • Primal sketch: represents brightness changes across visual field – results in a way of specifying the geometric shape of an object
    • viewer-centered sketch, which represents spatial locations of visible surfaces from viewer perspective
    • object-centered sketch: specifies the configuration of surfaces w/in object-centered coordinate frame
  • Damasio’s Model
    • perception involves evocation of neural activity pattern in primary and first-order ass’n cortex which corresponds to various perceptual features
    • Downstream, features combined in “local convergence zones”
    • No distinguish btwn memory and perception which bind features of a pattern into an “entity”
    • Predicts there can be no disorder of object recognition without perceptual dysfunction

Cognitive Neuropsychological Models

  • only received significant attn in visual recognition
  • Ellis and Young’s model: recognition begins by comparing viewer-centered and object-centered representation to stored structural descriptions of objects known as “object recognition units”

OTHER AGNOSIA TERMS

Autotopagnosia

  • disturbed body schema involving an inability to identify parts of one’s body, either to verbal command or by imitation
  • Gross autopagnosia is rare and is not observed in isolation
  • Limited forms include left-right disorientation and finger agnosia

Finger agnosia

  • bilateral loss of the ability to name or id the fingers
  • concept is linked to Gerstmann syndrome
  • failure on tests of finger recognition and finger localization may depend on specific demands of tasks employed (eg, aphasic misnaming, sensory deficits, spatial disorientation, attention pxs)

Static Object Agnosia

  • visual object agnosia, the effect of which is reduced when object is moved

ASSESSMENT OF AGNOSIA

  • Rule out alternative explanations
    • Ensure visual fields and visual acuity ok
    • Anomia: implies that stored representation of word has been lost; naming deficit is present regardless of sensory modality; recognizes meaning of object that cannot be named; in agnosia, object can readily be named thru different sensory modality
    • Aphasia: agnosic won’t demonstrate word-finding pxs in spontaneous speech and won’t be able to identify misnamed objects by circumlocution
    • Apraxia: can pt follow commands not requiring objects (e.g., wave, salute); can pt demonstrate object when not seen
    • Multimodal deficits are indicative of amnesia, dementia, or generalized impairments in semantic access
  • Determine which modality affected
  • Check apperception – matching, drawing, copying
  • Evaluate perception – figure/ground discrim, closure, synthetic ability, route finding
  • Evaluate visual memory: designs, objects, faces, colors
  • Evaluate associations: sorting, categorizing, pairing of similar objects, spontaneous use of object
  • Confrontation naming: for faces, ask male/female? Human/animal?
  • Test color perception

Aging and Memory

General Considerations

  • See also the broader discussion of Aging and Cognition
  • Many aspects of memory deteriorate w/ age
  • Decline affects recent memory more than immediate or remote
  • Ability to encode, store, and recall info is typically reduced in older adults; that is, memory processes become less effective, although the content of memory (knowledge) can continue to increase
  • Four different levels of memory functioning can be identified during life span
    • Peak performance reached at some point during adulthood; may be maintained by rare individuals who are said to enjoy superior aging
    • Age-appropriate decline; scores remain w/in range that is average for age
      • terms used here include age-associated memory impairment, benign senescent forgetfulness, and age-associated cognitive decline
    • Mild Cognitive Impairment: significantly below age-adjusted norm on standardized test, but without ADL impairment
    • Dementia: deterioration reaches level where interferes w/ ADLs

Normal Aging

  • Vast majority of neurons grow to be as old as owner
    • thus, each neuron exposed to cumulative effect of bio wear and tear throughout life
  • Aging depends on interaction of 3 variables:
    • time
    • genetic background
    • stochastic encounters w/ diverse events such as stress, hypertension, oxidation, trauma, etc.
  • Age-related changes are not necessarily intrinsic to aging – ie, aging may not cause the events but may increase the probability of encountering them; differentiating inevitable consequences of aging and cumulative (BUT preventable) impact of stochastic events embedded w/in time is very complex
  • Normal aging characterized by increased interindividual variability
  • Biological Components
    • Healthy aging ass’d w/ small loss of brain volume, but rate doesn’t accelerate w/ advancing age
    • Traditional view that aging is ass’d w/ massive loss of neurons is wrong
    • Cortical myelination seen to increase into 7th decade!
    • Aging brain retains considerable potential for structural plasticity
  • In sum, on AVERAGE
    • advancing age increases risk for losing neurons, synapses, transmitters, and cognitive acuity
    • but, many “age-related” changes might reflect preventable stochastic events
    • nonetheless, greatly enhanced vulnerability for dementing diseases

Mild Cognitive Impairment

Definition

  • Refers to transitional state between normal cognitive aging and mild dementia
  • It includes subjective memory complaint, corroborated by objective memory impairment on standardized test, but adequate general cognitive ability and ADLs ok
  • Since other forms of MCI exist, MCI emphasizing memory loss is termed Amnesic MCI

Heterogeneity

  • Individuals who present w/ MCI will not necessarily have same outcome since have different causes (could be DLB, FTD, etc.)

Progression

  • Individuals w/ MCI evolve to dementia at rate of 10-15% per year (normal is 1-2% per year)
    • variables that predict more rapid decline include apolipoprotein E4, atrophic hippocampi on MRI

Treatment

  • No effective treatment currently known, but cholinesterase inhibitors, anti-inflammatory agents, and anti-oxidants (eg, vitamin E) all theoretically make sense