Visual cortex
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The visual cortex is the part of the cerebral cortex of the brain that is responsible for processing visual stimuli. It is located at the back of the brain in the occipital lobe. It is highly specialized for processing information about static and moving objects and is excellent in pattern recognition. Anatomically, the visual cortex occupies the entire occipital lobe, the inferior temporal lobe (IT), posterior parts of the parietal lobe, and a few small regions in the frontal lobe. David H. Hubel and Torsten Wiesel received the Nobel Prize in Physiology or Medicine in 1981 for their work on the visual cortex.
The visual cortex occupies about one third of the surface of the cerebral cortex in humans. It is divided into approximately thirty interconnected visual areas. The first cortical visual area, the one that receives information directly from the lateral geniculate nucleus, is the Primary Visual Cortex, or V1.
V1 transmits information to two primary pathways, called the ventral stream and the dorsal stream:
- The ventral stream begins with V1, goes through Visual area V2, then through Visual area V4, and to the inferior temporal lobe. The ventral stream, sometimes called the "What Pathway", is associated with form recognition and object representation. It is also associated with storage of long-term memory.
- The dorsal stream begins with V1, goes through Visual area V2, then to Visual area V3, Visual area MT (also known as V5) and to the inferior parietal lobule. The dorsal stream, sometimes called the "Where Pathway" or the "How Pathway", is associated with motion, representation of object locations, and control of the eyes and arms, especially when visual information is used to guide saccades or reaching.
Neurons in the visual cortex fire action potentials when visual stimuli appear within their receptive field. A receptive field is a small region within the entire visual field. Any given neuron only responds to a subset of stimuli within its receptive field. This property is called tuning. In the earlier visual areas, neurons have simpler tuning. For example, a neuron in V1 may fire to any vertical stimulus in its receptive field. In the higher visual areas, neurons have complex tuning. For example, in the inferior temporal cortex (IT), a neuron may only fire when a certain face appears in its receptive field.
External links
- Webvision: Visual Cortex (http://webvision.med.utah.edu/VisualCortex.html)
| Sensory system - Visual system |
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Eye - Optic nerve - Optic chiasm - Optic tract - Lateral geniculate nucleus - Optic radiations - Visual cortex |