Topographic map (Neuroanatomy)

A topographic map is the ordered projection of a sensory surface, like the retina or the skin, or an effector system, like the musculature, to one or more structures of the central nervous system. Topographic maps can be found in all sensory systems and in many motor systems.

Visual system

The retina projects in an orderly fashion to the lateral geniculate nucleus of the thalamus and from there to the primary visual cortex; adjacent spots on the retina are represented by adjacent neurons in the lateral geniculate nucleus and the primary visual cortex. This projection pattern has been termed retinotopy.

Auditory system

The organ of Corti projects in an orderly fashion to structures in the brainstem (namely, the cochlear nuclei and the inferior colliculus), and from there to the thalamus and the primary auditory cortex; adjacent sites on the organ of Corti, which are themselves selective for the sound frequency, are represented by adjacent neurons in the aforementioned CNS structures. This projection pattern has been termed tonotopy.

omatosensory system

The cutaneous receptors of the skin project in an orderly fashion to the spinal cord, and from there, via different efferent pathways (dorsal column-medial lemniscus tract and spinothalamic tract), to the thalamus and the primary somatosensory cortex. Again, adjacent areas on the skin are represented by adjacent neurons in all aforementioned structures. This projection pattern has been termed somatotopy.

References

* Kandel ER, Schwartz JH, Jessell TM 2000. "Principles of Neural Science, 4th ed." McGraw-Hill, New York. ISBN 0-8385-7701-6