Overview
This lecture covers the anatomy and functional organization of the visual cortex, visual pathways, and conditions such as blindsight resulting from occipital cortex damage.
Visual Cortex Anatomy
- The occipital cortex is located at the back of the brain.
- The calcarine sulcus divides the superior cuneus lobe and inferior lingual gyrus.
- The primary visual cortex (V1) lies around the calcarine sulcus.
- Retinotopic maps in the visual cortex represent different parts of the visual field.
Visual Pathways
- Optic nerves meet at the optic chiasm, where half the fibers cross to the opposite side.
- The lateral geniculate nucleus (LGN) in the thalamus receives visual input for conscious perception.
- The right visual field projects to the left occipital cortex and vice versa.
- Optic radiations carry information from the LGN to the visual cortex.
Functional Streams in Visual Processing
- The dorsal stream ("where" pathway) goes to parietal regions and encodes motion and spatial location.
- The ventral stream ("what" pathway) goes to inferotemporal regions and encodes object form, color, and identity.
Clinical Conditions
- Carbon monoxide poisoning can damage the occipital cortex, leading to "blindsight."
- Blindsight patients lack conscious vision but can respond to visual stimuli reflexively.
- Damage here is typically permanent, as neurons in the central nervous system do not regenerate.
Key Terms & Definitions
- Occipital Cortex — posterior brain region for visual processing.
- Calcarine Sulcus — groove separating upper and lower regions of the medial occipital lobe.
- Primary Visual Cortex (V1) — initial cortical area for visual input.
- Retinotopic Map — spatial organization of visual input on the cortex matching retinal layout.
- Lateral Geniculate Nucleus (LGN) — thalamic relay center for visual information (light).
- Optic Radiations — nerve pathways from LGN to visual cortex.
- Dorsal Stream — pathway processing spatial location and movement ("where").
- Ventral Stream — pathway processing object identification ("what").
- Blindsight — ability to respond to visual stimuli without conscious visual perception.
Action Items / Next Steps
- Review visual pathways and retinotopic organization for exams.
- Study major visual deficits (e.g., blindsight, prosopagnosia, achromatopsia) in upcoming lectures.