Somatosensory System

Abstract

The somatosensory system of rats is of special interest, because rats use their facial whiskers to extract a wealth of information about objects in their environment, and the somatosensory system is specialized to process the information from receptors associated with their whiskers. Each whisker is represented by a distinct "barrel-like structure" in the trigeminal nucleus of the brainstem, ventroposterior nucleus of the contralateral thalamus, and the primary somatosensory area, S1, of contralateral cortex. The anatomical distinctiveness of these whisker representations has made the somatosensory system of rats popular for further study. Somatosensory information about touch from all parts of the body surfaces is relayed from the dorsal column nuclei, and the trigeminal complex to the contralateral ventroposterior thalamic complex (VP), and then to the somatosensory cortex. The somatosensory cortex includes a primary representation, S1, with a modular arrangement of "barrels" for whisker inputs and similar modules for other body parts, each surrounded by a cell-poor septal region. The rostral border of S1 consists of the dysgranular cortex, with a less developed layer 4, which may function in proprioception. Other cortical somatosensory areas include the second somatosensory area, S2, the parietal ventral area, PV, and a caudal belt of somatosensory cortex. These higher-level somatosensory areas all receive inputs from S1, while S1, S2 and PV receive thalamic inputs from VP.