Single unit oscillations in rat trigeminal nuclei and their control by the sensorimotor cortex.

Oscillatory activity at both the single and multiunit levels has been reported in most central nervous system structures, and is postulated as a key factor in information processing and coding. Rats provide an excellent model for oscillation-based information processing, since tactile perception of the environment is achieved by rhythmic movements of their whiskers and information-related rhythmic activity has been identified in the thalamus and cortex. However, rhythmic activity related to information processing has never been reported in the sensory trigeminal complex (STC), the first brain stem relay station for whisker-related tactile information. In the present work, we demonstrate the existence of neural oscillations in the vibrissae-related neurons of the nuclei principalis (Pr5), oralis (Sp5o), interpolaris (Sp5i) and caudalis (Sp5c). Rhythmic activity was associated with the main task of each nucleus, prominent in nuclei responsible for tactile vibrissae information processing (up to 17% oscillating neurons in Pr5 and 26% in Sp5i) and less conspicuous in those concerned with pain (8% oscillating neurons in Sp5o and in Sp5c). The higher percentage of oscillating neurons and higher frequencies in Sp5i than in Pr5 suggests an active role for rhythmic activity in integrating multivibrissa inputs. Oscillations are generated within the brainstem; data obtained from decorticated animals suggest the existence of a differential cortical control of the rhythmic processes in STC nuclei. Corticofugal activity modifies oscillation frequency and synchronization strength of the rhythmic activity mainly during tactile stimulation of the vibrissae.