Cortical Posterior Regions PDF

**Chapter Nine: Cortical Posterior Regions** **Posterior Cortical Areas** - Posterior cortical areas share a blood supply from the Posterior Cerebral Artery - Occipital lobe - Posterior areas of parietal lobe - Inferior and posterior areas of temporal lobe **When there is a posteri...

**Chapter Nine: Cortical Posterior Regions** **Posterior Cortical Areas** - Posterior cortical areas share a blood supply from the Posterior Cerebral Artery - Occipital lobe - Posterior areas of parietal lobe - Inferior and posterior areas of temporal lobe **When there is a posterior stroke, many areas can be affected due to the shared blood supply** **Video: posterior stroke isn't common, one of the most common symptoms is a visual field defect** **Diseases: Strokes** - 15-20% of all cerebral strokes occur in the cerebral posterior region - Often related to diabetes - Results in visual field cuts and ataxia - Don't cause language problems or hemiparesis -- so often misdiagnose initially **Diseases: Degenerative** - Less likely to be affected by degenerative diseases (e.g., dementia), but might be impacted - Posterior cortical atrophy - Degenerative, onset around 50-65 years old - Starts with occipital lobe and posterior temporal lobes - Results in dementia, including Alzheimer dementia and Lewy bodies dementia - Characterized by problems with - Object identification - Reading - Driving - Walking on uneven ground and stairs - Localizing objects - Navigating the environment - Gauging distance or depth - Spatio-motor problems, e.g., put key in a lock, use a remote **Visual Field Cuts** - Cuts after reading, writing, and communication with others (visual info such as gestures) - Awareness: usually aware of the visual field cut and can compensate by turning the head or moving eyes **Visual Fields** - Retina - Phototransduction in retina - Visual fields test - Contralateral sensorimotor control - Left occipital lobe processes signals from right visual field of each eye - Right occipital lobe processes signals from left visual field of each eye **Visual Pathways** - Light waves hit eyeballs -- refracted by lens and image inverts -- image goes to retina - Image is now backwards because... - Info in left visual field -- project to right side of retina - Info in right visual field -- project to left side of retina **Right Visual Pathway** - Starts on the left side of each eyeball and ends at the **LEFT** occipital lobe - So, there is contralateral innervation of the eyes, just like there is contralateral innervation of our body - Right visual pathway in the **left** eye - Axons carry visual information to the left occipital lobe - They don't have to cross the optic chiasm - Right visual pathway in the **right** eye - Axons carry visual information to the right occipital lobe - They do have to cross the optic chiasm **Left Visual Pathway** - Starts on the right side of each eyeball and ends at the **RIGHT** occipital lobe - So, there is contralateral innervation of eyes, just like there is contralateral innervation of our body - Left visual pathway in the **right** eye - Axons carry visual information to the right occipital lobe - They don't have to cross the optic chiasm - Left visual pathway in the **left** eye - Axons carry visual information to the right occipital lobe - They do have to cross the optic chiasm **Occipital Lobe & Visual Streams** - Signals to go the primary visual cortex in the occipital lobe via the thalamus. Primary visual cortex in each lobe processes these signals - Then signals travel from occipital lobe to temporal lobes and parietal lobes for more processing - Ventral stream: to temporal lobes (what it is) - Dorsal stream: to parietal lobes (where it is) **Homonymous Visual Field Cut** - Vision loss in same visual field (left or right) in both eyes - Contralateral vision loss - Types -- homonymous hemianopsia and homonymous quandrantanopsia **Homonymous Hemianopsia** - Lose half of visual field -- lose the same visual field (left or right) in both eyes. - Contralateral vision loss - If damage is unilateral (one occipital lobe only) = central sparing (center of vision in unimpaired). **Homonymous Quandrantanopsia** - Lose a quarter of visual field -- lose the same quarter of vision in both eyes - Quandrantanopsia results from smaller lesion than the lesion that causes hemianopsia - Contralateral vision loss **Cortical Blindness** - Caused by bilateral damage to the primary visual cortex - Can perceive light and dark - But can't perceive images **Visual Anosognosia** - Called Anton's syndrome - Cortical blindness without awareness that they are blind - Confabulate: may describe what they "see" but they don't see it - Damage to ventral pathway - Ventral pathway involves temporal lobe - So, can perceive an item but unable to recognize it or name it - Prosopagnosia - A form of visual agnosia - Can perceive people's faces, but not able to attach meaning (remember who they are or anything about them) -- even their own face sometimes **Visuospatial Perception** - Ability to localize and discriminate images and items, judge distance, orient yourself, and perceive dimensions - Impairments: distortions, trouble reading and writing, judging distance, face processing **Visuospatial Construction** - **Ability to draw, build, write** - **Example of problems: difficulty assembling pieces of something together, copying and drawing** **Spatial Cognition** - **Ability examples** - **Ability to recognize shapes and patterns** - **Ability to mentally rotate an image** - **Ability to learn to navigate a maze** - **Problems result in issues with organizing, selecting the correct size of something, etc.** **Speech** - **Speech disorders are rare with damage to posterior areas** - **Posterior circulation strokes can cause dysarthria If there is damage to:** - **Corticobulbar nerve tract (axons of upper motor neurons that connect premotor and motor cortex to the brainstem)** - **Brainstem** - **Cerebellum** **Language** - **Posterior damage can cause alexia (problems reading) and agraphia (problems writing)** **Swallowing Disorders** - **Dysphagia rarely occurs with damage to the posterior hemispheres** - **Absence of motor regions or pathways**