Variations in clustering of multielectrode local field potentials in the motor cortex of macaque monkeys during a reach-and-grasp task.

Abstract

There is experimental evidence of varying correlation among the elements of the neuromuscular system over the course of the reach-and-grasp task. Several neuromuscular disorders are accompanied by anomalies in muscular coupling during the task. The aim of this study was to investigate if modifications in correlations and clustering can be detected in the Local Field Potential (LFP) recordings of the motor cortex during the task. To this end, we analyzed the LFP recordings from a previously published study on monkeys which performed a reach-and-grasp task for targets with a vertical or horizontal orientation. LFP signals were recorded from the motor and premotor cortex of macaque monkeys as they performed the task. We found very robust changes in the correlations of the multielectrode LFP recordings which corresponded to task epochs. Mean LFP correlation increased significantly during reaching and then decreased during grasp. This pattern was very robust for both left and right arm reaches irrespective of target orientation. A hierarchical cluster analysis supported the same conclusion - a decreased number of clusters during reach followed by an increase for grasp. As most previous LFP studies have focused on the question of LFP amplitude, our study has contributed to the understanding of this signal and its relationship to movement by focusing on correlations. A sliding window computation of the number of clusters was performed to probe the capacities of these LFP clusters for detecting upcoming task events. For a very high percentage of trials (97.89%), there was a downturn in cluster number following the Pellet Drop (GO signal) which reached a minimum preceding the Start of grasp, hence indicating that cluster analyses of LFP signals could add to signaling the increased probability of the Start of grasp.Significance Statement The creation of muscular groups also called synergies for accomplishing an action is a well known feature of motor control. Since the motor cortex plays an important role in creating motor commands, it is only to be expected that such features might also be seen in this brain area. This study is among the first to show that alterations in local field potential (LFP) correlations as a function of task phase can be observed during the reach-and-grasp task by macaque monkeys. The LFPs recorded using multielectrode arrays in the motor cortex, showed increased correlations during reach, followed by decreased correlations at the start of grasp. This pattern was robust and held irrespective of which arm was employed or hand orientation.