Precentral cortical zones related to flexion and extension in two hindlimb movements in the monkey

Data suggest that relatively complex muscle synergies may be represented in the precentral cortex of alert rhesus monkeys while each performed two separate leg movements involving both legs and an ankle flexion-extension movement by the leg contralateral to the cortex studied.

Abstract

Single units were recorded in the leg region of precentral cortex in two alert rhesus monkeys while each performed two separate leg movements, a pedaling movement involving both legs and an ankle flexion-extension movement by the leg contralateral to the cortex studied. Most units could be classed as +F or +E for each movement, depending on whether they were activated during the flexion (+F) or extension (+E) phase of movement. The electrode penetrations were spaced 1 mm apart in a grid pattern (30–40 tracks/monkey). When the locations of +F or +E units for each movement were plotted on the grid of penetrations, they appeared to be organized into large homogeneous zones of either +F or +E cells with surprisingly little overlap between zones. The zones for the two different movements were similar but not identical. Consistency from one movement to the other improved if the pattern of EMG activity during the two movements was taken into account. These data suggest that relatively complex muscle synergies may be represented in the precentral cortex.