The predictive value for performance speed of preparatory changes in neuronal activity of the monkey motor and premotor cortex.

Three monkeys were trained in a precued reaction time (RT) paradigm. An initial preparatory signal (PS) provided complete, partial or no information about direction and extent of a wrist flexion/extension movement which was executed after the second, response signal (RS). A PS providing information about direction shortened the RT much more than a PS indicating movement extent. The activity of 464 task-related neurons was recorded in the primary motor (MI) and premotor (PM) cortex. Not only the timing and amplitude of mean activity changes were analyzed, but also trial-by-trial correlation analyses between RT and discharge frequency during the PS-RS interval were conducted. Correlations were stronger in the condition of information about direction than in conditions of information about extent or no information. Considering directionally selective neurons, correlations were stronger when the neuron's preferred direction than the opposite direction was precued. Correlation distributions were similar for MI and PM. Correlations were negative when preparatory activity increased during the PS-RS interval, and positive when activity decreased. Correlation analyses between behavioral performance and neuronal activity can thus be considered as a powerful tool to obtain a deeper insight into the functional mechanism of motor preparation.