Visual Cortex: New Research

All visual information that the human mind receives is processed by a part of the brain known as visual cortex. The visual cortex is part of the outermost layer of the brain, the cortex, and is located at the dorsal pole of the occipital lobe; more simply put, at the lower rear of the brain. The visual cortex obtains its information via projections that extend all the way through the brain from the eyeballs. The projections first pass through a stopover point in the middle of the brain, an almond-like lump known as the Lateral Geniculate Nucleus, or LGN. From there they are projected to the visual cortex for processing. Visual cortex is broken down into five areas, labelled V1, V2, V3, V4, and MT, which on occasion is referred to as V5. V1, sometimes called striate cortex because of its stripey appearance when dyed and put under a microscope, is by far the largest and most important. It is sometimes called primary visual cortex or area 17. The other visual areas are referred to as extrastriate cortex. V1 is one of the most extensively studied and understood areas of the human brain. Neurons in the visual cortex fire action potentials when visual stimuli appear within their receptive field. By definition, the receptive field is the region within the entire visual field which elicits an action potential. But for any given neuron, it may respond 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. The visual cortex receives its blood supply primarily from the calcarine branch of the posterior cerebral artery. This book presents the latest research in the field from around the globe.