SENSORY-EVOKED HIGH-FREQUENCY (GAMMA-BAND) OSCILLATING-POTENTIALS IN SOMATOSENSORY CORTEX OF THE UNANESTHETIZED RAT

A 64-channel epipial electrode array was used to investigate high-freq uency (gamma-band) oscillations in somatosensory cortex of the unanest hetized and unrestrained rat. Oscillations were evoked by manual stimu lation of the vibrissae and mystacial pad. Stimulation of the contrala teral vibrissae resulted in a significant increase in gamma-power duri ng 128-ms epochs taken just following stimulus onset compared to the p restimulus baseline. Stimulation of the ipsilateral vibrissae was comp letely ineffective in evoking gamma-oscillations in any animals. Senso ry evoked gamma-oscillations were constrained to primary (SI) and seco ndary (SII) somatosensory cortex. When averaged to an arbitrary refere nce of peak times in one of the channels, these oscillations exhibited a systematic temporal organization, propagating from the rostral port ion of SI to the barrel field proper, and finally to SIT. These spatio temporal characteristics were probably produced by intracortical pathw ays within rodent somatosensory cortex. The rostrocaudal propagation o f gamma-oscillations within the barrel field may also reflect whisking patterns observed when the vibrissae are used as a sensory array, sug gesting that synchronized gamma-oscillations may play a role in assemb ling punctate afferent information provided by the vibrissae into a co herent representation of a somatosensory stimulus. (C) 1997 Elsevier S cience B.V.