Cortices: Parietal and Temporal Lobes

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TEMPORAL LOBE

Hippocampus

  • Some controversy as to whether or not it encodes (material-specific) or represents only a cognitive/ spatial map (memory)
  • Rat studies suggests spatial map (i.e., lesion here, no longer able to find platform on Morris milk maze based on spatial cues from env; also stimulation and single cell recordings support this)
  • Monkey studies show that removed hippocampus, impaired location but not object memory
  • Although some human studies do suggest that hippocampus is involved with spatial memory (i.e., our FIST study-RH specific; topographical amnesia & spatial disorientation shown in patient HM), it’s not just spatial memory (perhaps material specific to HS) based on human lesion studies (TLE, HM, etc.), electrical stimulation and WADA testing (TLE), ERP studies, etc
  • Do see amnesia following hippocampal removal, as specific as CA1 (RB) and HM; however, even though they had poor memory for landmarks, also poor performance on WMS LM, verbal PA, and several “non” spatial memory tasks

Amygdala

  • Associated with emotional CC, emotional memory (saliency), emotion; see emotion and memory notes

Heschle’s Gyrus

  • Primary auditory cortex

Insular

  • Primary taste cortex

Association Cortices

  • Following damage to inferior T regions, often see agnosia (unable to recognize classes of objects) or ventral stream of the what (see V-S notes)

Symptoms of Temporal Lobe Lesions

  • Disturbed auditory sensation/ perception
  • Disturbed selective attn of auditory/ visual input
  • Disorder of visual perception (agnosia)
  • Impaired organization & categorization of verbal material
  • Disturbed language comprehension (WA)
  • Impaired LTM (HM)
  • Altered personality and affective behaviors (amygdala)
  • Altered sexual behaviors

PARIETAL LOBE

Anterior Zone (distinct from B)

  • Somatic sensations and perceptions
  • Somatosensory strip/postcentral gyrus

Posterior Zone

  • Integrating sensory input from somatic & visual regions
  • Guidance of movements to points in space in relation to objects in space (what Milner & Goodale argues the “where” system is really all about)
    • Mountcastle et al. showed that tertiary parietal region receives afferents of sensory representations of body movement in space
    • This region has substantial efferents to BG, spinal cord with respect to proximal but not distal movements (distal more F lobe)
    • Lesions/damage to this region produces severe bilateral apraxia when limb movements are required
    • Motor control of left and right parietal cortex is asymmetrical
  • Recognizing & producing abstract stimuli (lesion in angular gyrus disrupt reading)
  • Integrative fx of tertiary cortex (sensory integration)- polymodal regions (several imputs from different modalities converge here)
  • Construction of spatial coordination system to represent visual & somatic spatial worlds
  • Involved with eye movement (show in monkeys neurons which are sensitive to movement of eyes especially visually relevant stimuli- i.e., complex cells which are responsive to specific angles of light- spatial orientation)

Deficits Associated with Parietal Lobe Damage

  • Decreased visual attention
  • Unable to perceive more than 1 stimuli
  • Unable to follow moving target
  • Decreased accommodation & convergence
  • Optic ataxia
  • Unable to maintain fixation
  • Gaze apraxia
  • Abnormal visual search

Syndromes Associated with Parietal Lobe Damage

  • Balint’s Syndrome
    • Paralysis of voluntary gaze
    • Optic ataxia
    • Stimultagnosia (unable to recognize more than one components of visual field at once- piecemeal perception)
    • Verbal intelligence, language and verbal memory intact
    • Due to bilateral PO lesions/damage
  • Gerstman’s Syndrome
    • Associated with left parietal lobe damage
    • Finger agnosia (can’t id fingers on hands)
    • R/L confusion
    • Agraphia (inability to write)
    • Acalculia (inability to perform math operations)
    • Unilateral neglect
    • Apraxia (associated more with left parietal lobe damage)
    • Topographical disorientation/decreased navigation-unable to judge distances
    • Also can see defcits in visual location (where) and depth perception
    • Drawing/ constructional deficits
    • Spatial attention

Theory of Parietal Lobe Functioning

  • Involved with map of object location which is viewer centered (guide movements) rather than objected centered (TL, size, shape, color, etc.)
  • Evidence:
    • Single cell recordings in monkeys
      • Posterior P receives combination of inputs (motivational, motor sensory)
      • Discharge is enhanced when attending to move or moving toward an object
    • Human ERP studies (P100, P200)
      • Largest to contralateral stimulis
      • See cells in P region responding before eye movements & if subjects told to pay attention to a particular spot in one visual field, ERP largest when stimulus is presented there rather than somewhere else
    • rCBF/ PET
      • Roland showed increased BF bilaterally to parietal regions when direct attention to visual target
      • Also shown with other studies