Directional organization of sensorimotor oscillatory activity related to the electromyogram in the monkey

Objective: To investigate cortical control of the electromyogram (EMG). Methods: We examined the directed transfer function (DTF) between the EMG and local field potential oscillations in the monkey sensorimotor area during both an isotonic muscle contraction task and the rest condition with EMG silence. DTF computation based on a multivariate model is suitable for analyzing the directional structure Of a reciprocally interconnected system. Results: We found that DTF between the cortex and EMG in the beta band is predominantly centrifugal and largest at the anterior bank of the central sulcus. As for the cortico-cortical DTF within the sensorimotor area, the effective connectivity in the beta band was reciprocal across the central sulcus but was dominated by a posterior-to-anterior direction, especially during the muscle contraction task. The asymmetry of the DTF during the rest condition was inconsistent across the monkeys. Conclusions: These findings indicate the functional relevance of held potential oscillations in the post- as well as pre-central gyri in generating EMG rhythmicity. Significance: This supports the idea that information flow from the post- to pre-central gyri is a key element in volitional muscle contraction. (C) 2009 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.