Barrels, Vibrissae, and Topographic Representations
In the cerebral cortex, a barrel is a group of neurons shaped as such and visible with a microscope and in some cases with the naked eye. Each barrel is a cylindroid located in the middle layers of the somatosensory cortex of many rodents and certain other mammals and receives segregated inputs related to individual tactile organs called vibrissae or whiskers located principally on the face (see Fig. 1). A vibrissa consists of a central hair in a mechanically isolated hair follicle receiving a segregated and substantial sensory innervation known to be related to four different receptor specializations. Sensory inputs from the vibrissae can be modulated through motor control. Striated muscles actively move many of the whiskers back and forth during exploratory whisking behavior at frequencies of 7 Hz in rats and 15 Hz in mice. Each hair follicle is surrounded by erectile tissue, presumably under opponent autonomic control, which could dynamically alter the functional threshold of the tactile organs. The vibrissae are arranged in species-specific, stereotyped, grid-like patterns in which each vibrissa has a unique position.
KeywordsTrigeminal Ganglion Somatosensory Cortex Spinal Trigeminal Nucleus Erectile Tissue Topographic Representation
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