Cerebral Cortex

Projections of nerve fibers from the lateral geniculate bodies to area 17 of the occipital lobe form the optic radiation (see fig. 10.43). Because these fiber projections give area 17 a striped or striated ap pearance, this area is also known as the striate cortex. As mentioned earlier, neurons in area 17 project to areas 18 and 19 of the occipital lobe. Cortical neurons in areas 17, 18, and 19 are thus stimulated indirectly by light on the retina. On the basis of their stimulus requirements, these cortical neurons are classified as simple, complex, and hypercomplex.

The receptive fields of simple neurons are rectangular rather than circular. This is because they receive input from lateral geniculate neurons whose receptive fields are aligned in a particular way (as illustrated in fig. 10.46). Simple cortical neurons are best stimulated by a slit or bar of light located in a precise part of the visual field (of either eye) at a precise orientation.

The striate cortex (area 17) contains simple, complex, and hypercomplex neurons. The other visual association areas, designated areas 18 and 19, contain only complex and hypercom-plex cells. Complex neurons receive input from simple cells, and hypercomplex neurons receive input from complex cells.

Test Yourself Before You Continue

1. Describe the way in which ganglion cells typically respond to light on the retina. Why may a small spot of light be a more effective stimulus than general illumination of the retina?

2. How can the arrangement of the receptive fields of ganglion cells enhance visual acuity?

3. Describe the stimulus requirements of simple cortical neurons.

10. Sensory Physiology

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HPer Links of the Sensory System with Other Body Systems

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