Relationship of neuronal activity to gross movement-related potentials in monkey pre- and postcentral cortex

Abstract

The firing patterns of precentral neurons associated with conditioned hand movements have been extensively studied in the monkey 5,6,9,13. These studies have focused upon neural activity preceding movement and have established that the discharge of both pyramidal and non-pyramidal neurons increases prior to the onset of EMG-monitored muscular contraction. Since intracortical recordings are seldom obtainable in humans, efforts have been made to identify gross potential correlates of voluntary movement utilizing movement-synchronized averaged scalp EEG recordings4,1°,1'~. When recorded with repetitive self-paced movements, the human motor potential (MP) consists of a slow negative shift, beginning 0.5-2.0 sec before contraction (N I), a phasic negativity, beginning between 50 and 100 msec before contraction (N2), which is intermittently preceded by a small positive deflection (P l). A complex positive component follows the onset of movement and completes the MP. Comparable MPs have been recorded from the cortical surface of monkeys trained to perform self-paced wrist extension movements 1,1v. In both man and monkey the N2 component is maximal in amplitude overlying the contralateral precentral gyrus and in monkey transcortical recordings, N2 was found to invert in polarity exclusively within the precentral hand area 1. The timing and topography of this antecedent potential suggests that it is correlated with the cortical activity associated with corticospinal outflow ~°,1'~,1~. However, the relationship between the gross MP and neural firing patterns has not been directly examined. Although extracellular field potentials are generally considered to reflect synaptic currents, their relationships to neural firing patterns are extremely complex. [t is important to know the extent to which field potentials are capable of reflecting net population patterns of neural excitation and inhibition in order to evaluate the significance of the gross MP data obtained in human subjects and experimental animals. In this report we demonstrate direct relationships between the cortical loci and temporal pattern of neural firing and the gross potentials recorded from pre- and postcentral cortex in association with self-paced hand movements in the monkey. Three adult macaques (Maeaca mulatta) were trained to perform brief selfpaced wrist extension movements at intervals exceeding 2 sec. Contractions of muscles