CENTRAL NEURAL MECHANISMS OF TOUCH AND PROPRIOCEPTION

The argument is made that somesthesia is not a strictly passive proces s, and its central neuronal mechanisms cannot be studied in all their complexity and subtlety by applying passive stimuli to uninterested or unconscious animals. The case is clear for kinesthesia. Peripheral pr oprioceptive signals are altered by active muscle contractions, and th e central mechanisms of kinesthetic sensations should be studied durin g active movements. A similar case can be made for tactile discriminat ion. Ascending tactile afferents are subject to modulation during move ment. Moreover, the generation of a central neural representation of t he mechanical stimulus is only part of the tactile perceptual process. It is also influenced by the behavioral, attentive, and motivational state of the animal, whose effects can only be revealed in awake anima ls actively participating in discrimination tasks.