Lecture 9 Flashcards
There are two types of retinorecipient areas of the brain:
1) Image forming areas
2) Non-image-forming areas
Image-forming regions and examples
- The brains representation of the visual field
- Superior colliculus (SC) : coordination of reflexes and motor planning
- Dorsal lateral geniculate nucleus (dLGN) : relays information about what and where things are in the visual field
Non-image forming regions and examples
- Controls involuntary reflexes and brain state (arousal and emotions)
-Suprachiasmatic nucleus (SCN): controls circadian rhythms
-Medial Terminal Nucleus (MTN) / Nucleus of the Optic Tract (NOT): Optokinetic reflex, image stabilization - Olivary Pretectal Nucleus (OPN): pupillary light reflex
Visual pathway into the brain:
Optic nerve > Optic Chiasm > dLGN / SC > Visual Cortex
What are the two major visual pathways?
1) “Where” pathway (dorsal stream)
2) “What” pathway (ventral stream)
Ventral “what” pathway
- Primary visual Cortex (Occipital Lobe): Edges, orientation, simple shapes
- Visual Association Cortex (Temporal lobe): object and face recognition (and recognition of objects / places)
What causes lesions in the brain?
1) Stroke (ischemia)
2) Traumatic Brain Injury
3) Encephalitis (brain swelling from injury or infection)
Lesions along the visual pathway cause what deficits in the visual field?
- Complete loss of vision
- Central scotoma
- Tunnel Vision
2) Bitemporal hemianopia
3) Homonymous hemianopia
4) Quadrantanopia
5-6) Quadrantanopia
with Macular sparing
Why may Macular sparing occur?
because the visual cortex that perceives our central vision receives blood from two different arteries.
Lesions to the primary visual area or visual associative areas is known as ____________________.
Cortical blindness
Types of visual agnosia:
Agnosia: inability to interpret sensations and hence to recognize things, typically as a result of brain damage.
1) simultagnosia
2) prosopagnosia
Simultagnosia
- Balint’s syndrome
- In this condition, patients can only recognize single object at a time. They fail to comprehend the entire visual scene.
-a patient with simultanagnosia would be able to name objects in the picture but would not be able to explain what was going on. - Most scientists think that there is deficit or injury to the visuospatial processing centers in the parietal cortex (”where” pathways).
- Some cases have been observed in patients with Alzheimer’s Disease
Prosopagnosia
- “face blindness”
- Loss of face perception. Patients can see faces but are unable to recognize the faces they see. This includes recognition of one’s own face.
- Cause by defects Fusiform Face Area (FFA) due to injury (stroke) or congenital (birth defect)
Hemispatial Neglect
- visual neglect
-In visual neglect, the patient lose attention and awareness to one-side of their visual field. - Most cases are the result of stroke in the contralateral parietal or frontal cortex.
- This affects the dorsal visual pathway.
Synesthesia
-A phenomenon where one cortical/sensory pathway is connected to secondary cortical/sensory pathway.
Examples:
* Seeing colors with numbers (Grapheme-color synesthesia)
* Seeing colors with different tones (Chromesthesia)
* Increased grey matter found in Fusiform gyrus (colors) and V4
(number, letter area). Possibly increase in connectivity between
these areas.
