Neglect

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DEFINITION

  • Neglect: a failure to respond to, report, or orient to novel or meaningful stimuli presented to the side opposite the lesion
  • NOT attributable to sensory, motor, or memory deficits deficit of looking, detecting, listening, and exploring NOT seeing, hearing, or moving
  • Like aphasia or amnesia, neglect is a “network syndrome” and represents damage to one or more components of a distributed network
  • Also has been described as unilateral spatial agnosia, amorphosynthesis, left-sided fixed hemianopia, hemi-inattention, hemineglect, hemispatial agnosia, etc.

HISTORY

  • Jackson (1867) first to present well-documented account
  • Extensively described by Brain (1941)
  • 1970s saw resurgence in interest

GENERAL CLINICAL ISSUES

  • Characterized by reduction of neural resources mobilized by sensory events and motor plans on left
  • Most dramatic aspects occur in visual sphere, but also seen in auditory, somatosensory, olfactory
  • Neglect behaviors can be classified into 3 components:
  • Sensory-Representational
    • Sensory neglect or inattention is a form of selective unawareness
    • May be defined by its modality (eg, tactile, visual, auditory) and distribution (eg, hemispatial, personal)
    • Pts behave as if sensory events on L lost impact on awareness, especially when competing events on R
    • Probed w/ tests of extinction, line bisection, and covert attentional shifts
    • Another useful probe is to have pt close eyes and point toward body midline; usually pt rt of midline
  • Motor-Exploratory
    • Reluctance to scan and explore L hemispace
    • Probed w/ tasks of target detection (the more difficult, the more sensitive in detecting; eg, letters better than lines; complex shapes better than letters, etc.)
    • L-sided target detection failures reflect both: decreased tendency to explore L and attraction to R side
    • Neglect dyslexia involves failure to read words on left side of page
    • “Intentional Neglect” or “limb akinesia” reluctance to move limbs on L (in absence of damage to corticospinal system)
    • “Hemispatial akinesia” is better movement in ipsilesional than contralateral space
    • “Hypokinesia” is milder form of intentional neglect, in which delay in initiating movement
  • Limbic-Motivational
    • Major role of attentional system is to shift attentional searchlight toward emotionally or motivationally salient events
    • Neglect pts devalue the L side of space and act as if nothing of importance could happen on that side

CLINICAL MANIFESTATIONS OF NEGLECT

  • Inattention
    • failure to report or respond to stimuli presented contralaterally, but may be able to detect the stimulus if pt’s attn is directed to that side (so different than hemianopia or other primary sensory pxs)
    • may even fail to recognize that their contralateral extremities are their own
    • in milder cases they will recognize that the limbs are theirs (b/c they’re attached), but they refer to them as though they were objects
  • Allesthesia (sometimes referred to as allochiria)
    • disturbance of body schema perception in tactile modality in which stimulation on one side of body is perceived as located on other side
    • similar phenomena may occur in other modalities
  • Sensory Extinction to Double Simultaneous Stimulation
    • patients w/hemi-inattention usually improve so that they are able to detect and lateralize stimuli, but often when they are stimulated bilaterally they fail to report the contralateral side
    • may affect one or more sensory modalities
  • Action Intentional Disorders (Motor Neglect); 4 types:
    • Akinesia: pt fails to spontaneously use contralateral body part, although when focusing on that extremity they may show good strength; may involve different body parts (eyes, arms, head)
    • Hypokinesia: may initiate response, but after a long delay; may be obvious or need RT testing
    • Motor Extinction: patients who do not demonstrate akinesia when they move one limb may demonstrate contralateral akinesia when they must move both limbs simultaneously
      • may report moving both limbs, but will only move one
    • Motor Impersistence: inability to sustain motor act; have them move for 10-20 seconds
  • Spatial Neglect
    • Spatial neglect may occur in all three dimensions of space: horizontal, vertical, and radial (near, far)
    • patient neglects the hemispace contralateral to the injured hemisphere
    • seen on tests of line bisection, target cancellation, and drawing
    • frequently fail to dress or groom abnormal side
    • hemispatial neglect pts can use both a body-centered frame of reference and environmental frame of reference
  • Neglect can also be classified by one of the following sectors of space
    • Personal neglect: attn disturbances to contralateral side of body (eg, fail to groom or even dress one side of body)
    • Peripersonal neglect: attn disturbances w/in reaching or grasping space
    • Far extrapersonal neglect: attn disturbances may be detected only when stimuli are out of reach

ASSOCIATED CLINICAL BEHAVIORS/SYNDROMES

  • Anosognosia (also associated w/other disorders)
    • unawareness or denial of deficits – even sometimes that the paretic limb belongs to them
    • most associated with damage to rt. hemisphere (when the left hemisphere is damaged, more likely to have a catastrophic reaction)
    • behavioral examples: if you ask them to do a task with their impaired limb, they may say, “oh, I’m left handed” (w/rt hemiplegia), or they may say they have done the task when they haven’t
    • can be specific to particular disorders; e.g., Bisiach studied patients w/both hemiplegia and hemianopia; patients were unaware of either or both disorders (depending on the patient)
  • Anosodiaphoria
    • Pt will admit to sensory/motor impairment but be entirely unconcerned about it (in psychogenic pts, similar phenomenon called La Belle Indifference)
    • May follow a period of anosognosia
  • Allokinesia
    • pt moves ipsilateral extremity when tasks requires movement of contralateral extremity
  • Visuospatial deficits

FUNCTIONAL NEUROANATOMY OF NEGLECT

  • Neglect much more frequent, severe after lesions of R hemisphere since R hemi specializes in spatial distribution of attention
    • Left hemi attributes salience and directs attn to RIGHT side
    • Right hemi attributes salience and directs attn to BOTH sides (w/ slight contralateral bias)
    • Right hemi devotes more neural resources to spatial attn
  • Attentional network includes three cortical regions; any component can cause neglect (Mesulam)
  • Parietal component (inferior parietal lobe)
    • Seems to play its key role in spatial attn NOT as multimodal spatial map but as critical gateway for linking distributed channels of motor output
    • When parietal component destroyed, individual input/output channels may remain intact but can’t be integrated
    • Small lesions rarely lead to neglect, usually large and involve subcortical components
  • Frontal component
    • May play its critical role in network by converting plan and intentions into specific sequences of motor acts that shift the focus of attn; Frontal Eye Fields select/sequence individual acts needed to explore
    • Lesions confined to right frontal lobe can cause neglect just as severe as parietal lesions
    • Important regions unclear, but likely Frontal Eye Fields or inferior frontal gyrus
  • Limbic component
    • Cingulate component least understood, but may play critical role in identifying motivational relevance of extrapersonal events and sustaining level of effort during attentional tasks
    • Can have neglect w/ lesions to cingulate gyrus, though rare
    • Cingulate component may have two parts:
      • anterior part reflecting global attentional engagement
      • post part which may participate in more differentiated lateralized shifts of relevance and focal attn
  • Subcortical components of attentional network:
    • Includes thalamus, striatum, and superior colliculus
    • Thalamic neglect: deficit attributed to problem w/ engaging, not the disengaging problem seen w/ parietal lesions

ETIOLOGY

  • Usually consequence of focal lesions involving right
    • Most common cause is CVA; also can see w/ fast-growing tumor, seizures
  • More generalized injury rarely leads to neglect so don’t typically see from toxic-metabolic encephalopathy, subdural hematoma, neurodegenerative diseases, head injury

MECHANISMS UNDERLYING NEGLECT

Precise mechanisms still unclear, but over the years, literature divided into two camps (w/ attentional hypothesis now more accepted):

Representational Hypotheses

  • Bisiach (1978, 1981) (representative of approach)
    • Posterior parietal cortex contains an elaborate spatial representation of the external world
    • Unilateral injury causes unilateral loss of spatial representation and thus neglect
    • Classic experiment: pts describe the Piazza del Duomo (cathedral) in Milan; pts failed to describe landmarks imagined on left side of scene
    • Interpretation of data unclear
    • Could mean: a) impaired representation b) impaired scanning of intact representation c) or inability to attend to contralesional hemispace
    • Seems clear that improved performance upon cueing pts to left implies attentional component, which not readily explained by representational view

Attentional Hypotheses (sample views below)

  • Heilman’s (1977) Unilateral Akinesia Hypothesis ~ theory – associated with hypoarousal
    • A defect in orienting to stimuli due to a disruption of the system whose function it is to “arouse” the individual when new sensory information is present
    • Neglect results from decreased activation of arousal systems of damaged hemisphere
    • Effect of unilateral decrease in arousal is selective loss of orienting rx to contralateral hemisphere
    • Damaged hypoaroused hemisphere rendered akinetic
    • View revolutionized conceptualization of neglect, but number of problems (e.g., why don’t most severe cases of neglect follow damage to reticular activating system)
  • Posner’s (1982, 1984) Covert Orienting Hypothesis ~ disengage, shift, engage model of attention
    • Neglect results from impairment in mechanisms allowing attn to be shifted away from intact hemispace, rather than an inability to direct attn to impaired side
    • Neglect pts find it remarkably difficulty to disengage attn from ipsilesional hemispace
    • First to accommodate findings that cueing reduced severity of neglect errors, but selective deficit in visual attn can’t explain all findings since neglect not specific to visual modality
  • Mesulam’s Attentional Network Hypothesis (lots of above based on Mesulam’s model)
    • Neglect is a “network syndrome” and represents damage to one or more components of a distributed network (Involves the above outlined parietal, frontal, and limbic components)
    • Represents a domain-specific impairment of spatial attention

ASSESSMENT ISSUES

  • Differential Diagnosis
    • Need to rule out primary sensory deficits, which are not ameliorated by attentional cues
    • Unilateral hearing loss does NOT occur following unilateral lesions (if does, then it’s neglect)
    • Visual field cuts are NOT affected by the position of the eyes in space (neglect is)
    • Pts w/ neglect show normal sensory evoked potentials
  • Assessment should include at least three modalities
    • auditory
    • visual
    • somesthetic
  • Informal Testing (bedside: gaze, dressing, motor, etc.)
  • Standardized Testing
    • Cancellation tasks: look at omissions and search strategy
    • Line bisection: large deviations to ipsilateral side
    • Drawing: copy or draw clock (which is less sensitive to visuoconstructional deficits)
    • Reading and writing

TREATMENT

  • First and foremost, should treat underlying cerebral disease
  • Management of environment
    • need to arrange the environment to reduce risk of injury
    • since neglect is often in reference to patient’s midsagittal plane, pt should be positioned such that environmental stimuli are on right
    • reduce competing or distracting stimuli
    • when detecting stimuli not critical, pts should receive stimuli in neglected fields since may be therapeutic
  • Training
    • some evidence that pts w/ neglect can be trained to explore contralesional space w/ operant techniques
    • But, may remain task specific and not generalize
  • Cueing
    • Attentional cues may help pt attend to contralesional hemispace
    • Bottom up cues include providing novel stimuli
    • Top down cues include providing directions to attend to neglected side
    • Ultimate goal would be to have them know to search to left, before engaging environment
    • Motor neglect may improve if have pt uses left arm (even small movements of left may help)