Primary visual cortex
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The primary visual cortex (usually called V1) is the most well-studied visual area in the brain. It is also the simplest and first cortical visual area. Situated around the calcarine sulcus in the occipital lobe, it is the most caudal structure in the brain. It receives signals relayed from the retina via the lateral geniculate nucleus of the thalamus. Thus, primary visual cortex is only one synapse away from the retina.
The functionally defined primary visual cortex is approximately equivalent to the anatomically defined striate cortex. The name "striate cortex" is derived from the stria of Gennari, a distinctive stripe visible to the naked eye that represents myelinated neurons in layer 4 of the gray matter. The primary visual cortex is also anatomically equivalent to Brodmann area 17, or BA17. Brodmann areas are based on a histological map of the human brain created by Korbinian Brodmann.
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History
David Hubel and Torsten Wiesel were the first scientists to show that neurons in primary visual cortex show tuning for oriented lines. Supposedly they were presenting visual stimuli on slides to a cat while recording neural signals. They were unable to find any stimulus that would make the cell fire until they presented a slide which had a crack on it. Although they won the Nobel Prize in medicine for later work, it is this discovery for which they are most famous today.
Current Research
Research on the primary visual cortex can involve recording action potentials from electrodes with the brain of cats, ferrets, or monkeys, or through recording intrinsic optical signals from animals, or fMRI signals from human and monkey V1.
One recent discovery about V1 is that signals measured by fMRI show very large attentional modulation. This result strongly contrasts with macaque physiology research showing very small changes (or no changes) in firing associated with attentional modulation.
Other current work on v1 seeks to fully characterize its tuning properties, and to use it as a model area for the canonical cortical circuit.
Lesions to primary visual cortex usually lead to a scotoma, or hole in the visual field. Interestingly, patients with scotomas are often able to make use of visual information presented to their scotomas, despite being unable to consciously perceive it. This phenomenon, called blindsight, is widely studied by scientists interested in the neural correlate of consciousness.
References
- Peters, Alan (ed), and Kathleen S. Rockland (ed). 1994. Cerebral Cortex: Primary Visual Cortex in Primates v. 10 (Cerebral Cortex). Kluwer Academic / Plenum Publishers
- Peters, Alan (ed) and Bertram Payne (ed). 2001. The Cat Primary Visual Cortex Academic Press.
External link
- The Primary Visual Cortex by Matthew Schmolesky (http://webvision.med.utah.edu/VisualCortex.html)