Abstract
The nervous system executes movements using both corticospinal and reticulospinal tracts, but the relative contributions of these pathways have been shown to depend on the anatomical and functional characteristics of the movement. For example, using TMS, it has been demonstrated that the contribution of reticulospinal drive is larger for wrist flexion than for extension. In addition, movements triggered involuntarily by a startling acoustic stimulus appear to involve greater reticulospinal drive than those voluntarily initiated. Previous studies have suggested that significant EMG-EMG coherence in the alpha and low beta bands (10-20Hz) represents a potential measure of reticulospinal drive. The current study examined coherence from contralateral homologous muscle pairs during constant or modulating force production tasks involving wrist flexion/extension, as well as gross/fine actions of the hands. It was expected that flexion movements, gross movements, and constant force tasks would result in higher alpha band coherence than extension, fine, and modulated movements, indicative of greater reticulospinal drive. Contrary to expectations, results showed greater coherence in the alpha (8-15Hz) band for wrist extension with constant force, as well as for all wrist movements during force modulation compared to constant force. Similarly, alpha band coherence in bilateral intrinsic hand muscles was stronger in the precision grip compared to the power grip, as well as during modulated versus constant force. Our findings suggest that the 8-15Hz bandwidth may also represent cortical involvement, at least in voluntary wrist and hand movements, and that responses with greater reticulospinal drive are not reflected in increased alpha band coherence.
