LESIONS OF THE VISUAL SYSTEM - 50
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- Describe Spatial hemineglect?
- Lesion at the right-side parietal-temporal lobe lesion: TPO junction): patients ignore their entire left visual world. Could be a superior temporal gyral lesion.
- Describe Balint syndrome?
- (bilateral parietal-temporal lobe lesions): spatial-temporal disorientation, generalized loss of attention, combining paralysis of visual fixation, optic ataxia, and impairment of visual fixation, inability to execute voluntary movement in response to visual stimuli.
- What is thought to underlie spatial hemineglect?
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Cortico-subcortical network thought to underlie spatial neglect. The putamen/nucleus caudatus (striatum) and pulvinar are the subcortical nuclei that are associated with neglect behavior. They have direct anatomical connections with the superior temporal gyrus.
This negelct order is probably a sense of balance order. - Effect of Lesion on the left side of the Wernicke area
- you cannot understand what people are saying.
- Achromatopsy is?
- (loss of color vision): lesion of area V4.
- Akinematopy is?
- (loss of perception of motion): lesions of area V5 (MT/MST).
- Agnosia is?
- deficit in object perception while vision is preserved): lesions in the temporal lobe as well at the temporal-occipital border.
- Prosopagnosia is?
- (a loss of the ability to recognize faces): lesion in the left occipital lobe. After particular lesions of the right temporal lobe, the ability to recognize faces is preserved, however, the patients are unable to gage the emotional content of facial expressions.
- Alexia is?
- (loss of ability to read): lesion of the left occipital cortex or of the angular gyrus.
- Differentiate btw dorsal and ventral pathway?
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Magno and parvo go into the dorsal stream of the visual processing centers in the cerebral cortex. V1 is the primary visual cortex. The dorsal (parietal) stream deals with motion, depth, and spatial formation. The ventral (inferior temporal) stream deals with object vision, form and color. -
Disscuss:
1. VIP
2. Middle Temporal
3. MST -
VIP does motion perception of the close stimuli. The inferior parietal area projects in the prefrontal cortex.
Middle temporal has small receptive fields. MST have large receptive fields.
Neurons in the middle temporal area (MT) are selective for local 2D-motion
Neurons in the medio-superior-temporal area (MST) are selective for global optic flow/analysis of self motion. - Discuss visual fields esp . in lateral eye animals compared to frontal eye animals?
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For the lateral eyed animals, the left visual field is located in the right geniculate and opposite for the right visual field. In order to keep that same property in humans, the eyes have to be “re-wired†to do so. Looking at the picture, the left eye has to be represented by the right geniculate which is why in the left eye, the visual field is the nasal retina of the right eye which crosses over to the right geniculate and on the right eye, the portion of the left eye is represented by the temporal retina which stays ippsilateral so as to go to the right geniculate making it to where the left eye is represented in the right geniculate. The same goes for the right eye.
The upper hemisphere projects to the lower retina and the lower hemisphere projects to the upper retina.
The temporal retina looks out on the nasal hemisphere. - Effect of Optic nerve lesion?
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monocular blindness - Effect of Sagittal optic chiasm section?
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bitemporal hemianopsia. - Optic tract lesion?
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contralateral homonymous hemianopsia. - Effect of Lesion of Meyer’s loop
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upper contralateral quadrantic anopsia (loss of vision in the upper quadrant of
the contralateral half of the visual field of both eyes). - Partial lesion of the visual cortex in the upper bank of the calcarine sulcus?
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deficit in the inferior quadrant
of the contralateral visual field. - Partial lesion of the visual cortex in the lower bank of the calcarine sulcus?
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deficit in the superior
quadrant of the contralateral visual field. - Lesion involving both banks of the calcarine sulcus?
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leading to a more extensive deficit, i.e., a
contralateral homonymous hemianopsia,however sparing the foveal representation. - Describe Projection of input from the retina to the visual cortex?
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Information from the superior visual hemifield is received by the inferior halves of the retinae and is transmitted via Meyer’s loop to the inferior banks of the primary visual cortex.
Information from the inferior visual hemifield is received by the superior halves of the retinae and is transmitted to the superior banks of the primary visual cortex. In the lateral geniculate, you have representation from both eyes. -
1. What is the dual blood supply to the to the macular cortical representation of the eye?
2. What is the significance of this dual blood supply to the macular cortical representation? -
The dual blood supply to the macularof the eye is:
1. Posterior cerebral artery
2. Middle cerebral artery
Due to this supply to cortical representation, macular vision may be spared after posterior cerebral artery occlusion. - Visual
- Lesion