Perception, Agnosia and related disorders

Question 1

Retinal ganglia cells

Answer 1

• M-cells:
  10% of ganglia. color blind.
  large receptive field; high contrast sensitivity; high temporal resolution; low spatial resolution
• P-cells:
  80% of ganglia. color competent.
  small receptive field; small contrast sensitivity; poor temporal resolution; high spatial resolution
• Gamma-cells:
  10% of ganglia. heterogenous properties

Question 2

Retina to Visual cortex

Answer 2

1. Lateral geniculate nucleus:
   Magno cells, Parvo cells, Interlaminar.
   Reorganization in: origin, retinotopy, function
2. Retino-geniculo-striate pathways:
   - N. Suprachiasmaticus: sensitive to dark/light, related to sleep procedure;
   - Colliculus superior: in brainstem, programming the eye movement which is so fast and reflexive ;
   - Corpus geniculatum lateral: 90% of fibers going back of the brain.

Question 3

Retinotopy

Answer 3

in primary visual cortex (V1, BA 17) in calcarine fissure,
high degree of specialization (like the sensory-motor homunculus):
up/down, right/left, polar/rostral

Question 4

Lesions in Optic Nerve
(EXAM)

Answer 4

• monocular blindness: lesion in one eye or optic nerve > total blindness in one eye.
• bitemporal hemianopia: lesions of the optic chiasm, the area where the optic nerves from the right and left eyes cross near the pituitary gland > visual defect in temporal areas in both eyes.
• right-sided nasal hemianopia: lesion in right optic nerve at chiasm (the part which does NOT cross at the chiasm i.e. the nasal part) > visual defect in right nasal visual field.
• homonymous hemianopia: lesion in one-side optic TRACT after chiasm > visual field defect involving either the two right or the two left halves of the visual fields of both eyes
• quadrantanopia : lesions to the contralateral inferior parts of the posterior visual pathway > visual defect in one quarter of field, involving either the two right or the two left halves of the visual fields of both eyes
• macular sparing: unilateral visual cortex lesions > partial loss of vision in the same half of both eyes with the center, the macula, spared

[pic]

Question 5

V1 to higher Visual cortex

Answer 5

the higher data go in visual processing:
the more complex processing,
the less retinotopy

V1 (contrast & orientation)
> V2 (figure-ground separation):

> > Ventral path [what, object recognition => through the memory area]:
V4 (color, form) > IT

> > Dorsal path [where, how => through the motor area]:
V3 (disparity) > V5/MT (movement) > MST ( moving stimuli with directional selectivity) > PPC

• dMST: object motion
• lMST: retinal slip by self or eye motion

Question 6

Achromatopsia (color defect)

Answer 6

• a condition characterized by a partial or total absence of color vision, disability to perceive any colors; seeing only black, white, and shades of gray.
• combined with:
• upper visual field defect
• other agnosia

Question 7

Agnosia

Answer 7

disability to identify objects, persons, or sounds using one or more of their senses despite otherwise normally functioning senses.

• Apperceptive agnosia : Impairment of high level percepts.
  Retained semantic knowledge accessible through other modalities such as auditory, which is not the case for associative visual agnosia.
  Lesions: toxic or anoxic brain damage
  bilaterally
• Associative agnosia: Inability to activate semantic identifying information. More general loss of semantic knowledge, with no ability to access this via any sensory modality.
  + no difficulties in perception, only in naming and semantic knowledge.
  Lesions: bilateral temporal lesions
  HSV

Question 8

Alexia without Agraphia

Answer 8

sees letters but difficulties to comprehend,
difficulties in spatial orientation,
intact writing undisturbed

Lesions: visual-verbal disconnection

Question 9

Prosopagnosia (Face recognition defect)

Answer 9

Inability to recognize people by looking at their face.
Ventral occipitotemporal pathology (especially right side) is observed.

combined with:
* upper visual field defect
* other agnosias
* achromatopsia

Lesions: gyri lingualis & fusiformis

Prosopagnosia Assessments:
- Mooney closure test (faces with/without proper orders)
- Benton-Van Allen face recognition test (defining age/sex/characteristics in silhouettes)
- Benton-Test

Question 10

Akinetopsia (Motion recognition defect)

Answer 10

lesion in V5 or around it. Deficit with motion recognition. They recognize the objects but can not process data about their motions (fast objects like jump instead of moving)

combined with:
* lower quadrant field
defects
* optic ataxia
* neglect

Lesion: bilateral medial temporal gyrus
> good remission

Question 11

Pathology of neglect

Answer 11

mostly right hemisphere in inferior parietal lobe
» If we had a lesion in left hemisphere, the right part can compensate for the left side, so we wont have the neglect

Question 12

Neglect

Answer 12

contralateral neglect of sensory stimuli or motor function

extend correlates with size and
location but not with gender or
age

combined with:
* hemianopia
* neglect in further modality
* anosognosia

Lesion:
mostly right parietal lesions
but also cingulum, prefrontal cortex,
thalamus, striatum