[Modulation of cutaneous evoked potentials during the period preparatory to a reaction time task in the cat]

Evoked potentials (EP) were elicited in four cats either when they sat still or when they performed a reaction time (RT) task. The foreperiod (FP) of the RT situation started with the cat placing his paw on a platform and ended 1.5 sec later with the vibration of the platform, used as a signal to withdraw the paw. The paw was electrically stimulated, once per trial, during the last second of the FP. Evoked potentials were recorded in the medial lemniscus (ML), in the thalamic nucleus centrum medianum (CM), in the internal capsule (IC) and over the anterior suprasylvian gyrus (ASSG). On the average, the EPs recorded in the CM, in the IC and over the ASSG (early and late waves) were significantly reduced during the FP. The EPs recorded in the ML did not show any significant change. The reduction in the EPs amplitude decreases along the FP, being the less at the time of arrival of the response signal. Neither the amplitude nor the time course of the EPs are correlated with the RT duration. These results are discussed with reference to the concepts of preparation for movement and of anticipation of the response stimulus.