Posterior Cortical Areas and Stroke Effects

Posterior Cortical Areas

• Posterior cortical areas share a blood supply from the posterior cerebral artery, including the occipital lobe, posterior parietal lobe, and inferior/posterior temporal lobe.
• A stroke affecting these areas can cause various symptoms due to the shared blood supply.

Posterior Stroke Symptoms (Video)

• Visual field defects are a common symptom of a posterior stroke.

Posterior Stroke Diseases

• Strokes:
  • 15-20% of all cerebral strokes occur in the posterior region.
  • Often related to diabetes.
  • Frequently present with visual field cuts and ataxia.
  • Initial misdiagnosis is common as these strokes don't typically lead to language problems or hemiparesis.
• Degenerative Diseases:
  • Less likely to be affected by degenerative diseases (e.g., dementia) but might be impacted.
  • Posterior cortical atrophy in people aged 50-65.
  • Starts with occipital and posterior temporal lobes.
  • Symptoms include dementia (like Alzheimer's and Lewy bodies dementia).
  • Characterized by problems with object identification, driving, walking on uneven surfaces, localizing objects, navigating, gauging distance/depth, and spatio-motor skills.

Visual Field Cuts

• Visual field cuts affect reading, writing, communication, and visual information like gestures.
• Patients are usually aware of the cuts and compensate by moving their head or eyes.

Visual Pathways (Page 2)

• Visual Fields: Phototransduction in the retina, contralateral sensorimotor control, and visual field testing. The left occipital lobe processes signals from the right visual field of each eye, and the right occipital lobe processes signals from the left visual field of each eye.
• Visual Pathways: Light waves hit the eyeballs, then are refracted by the lens and the retinal image is inverted. Information from the left visual field projects to the right side of the retina and vice-versa.
• Right Visual Pathway: Starts on the left side of each eyeball and ends in the left occipital lobe. Information from the right eye travels to the left occipital lobe. Axons don't cross the optic chiasm in this case. Information from the left eye needs to cross the optic chiasm.
• Left Visual Pathway: Starts on the right side of each eyeball and ends in the right occipital lobe. The information from the left eye goes to the right occipital lobe, and the optic chiasm isn't crossed. Axons from the right eye also go to the right occipital lobe, but the optic chiasm is crossed in this case.

Occipital Lobe & Visual Streams (Page 3)

• Homonymous Visual Field Cut: Vision loss on the same visual field (left or right) in both eyes.
• Types include homonymous hemianopsia (loss of half a visual field) and homonymous quadrantanopsia (loss of a quarter of a visual field).
• Cortical Blindness: Bilateral damage to the primary visual cortex resulting in the inability to perceive images although light and dark can still be perceived.

Visual Anosognosia (Anton's Syndrome)

• A condition where people with cortical blindness lack awareness of the blindness. They may confabulate (falsely describe what they "see").

Visuospatial Perception (Page 4)

• Ability to locate and discriminate objects, judge distance, orient the body in space, and perceive dimensions.
• Impairments can include distortions, trouble with reading, writing, and judging distances.

Visuospatial Construction (Page 4)

• Ability to draw, build, copy.

Spatial Cognition (Page 4)

• Ability to recognize shapes, use mental rotation, navigate mazes, and spatial organization.

Speech Disorders (Page 4)

• Posterior circulation stroke can cause dysarthria (difficulty with articulation) if corticobulbar nerve tracts are damaged.

Language Disorders (Page 4)

• Posterior damage can lead to alexia (reading problems) and agraphia (writing problems).

Swallowing Disorders (Page 4)

• Dysphagia (difficulty swallowing) rarely occurs with damage to the posterior hemispheres due to the absence of necessary motor regions or pathways.