Corticospinal Beta-Range Coherence Is Highly Dependent on the Pre-stationary Motor State

Abstract

During steady muscle contractions, the human sensorimotor cortex generates oscillations in the beta-frequency range (15-30 Hz) that are coherent with the activity of contralateral spinal motoneurons. This corticospinal coherence is thought to favor stationary motor states, but its mode of operation remains elusive. We hypothesized that corticospinal beta-range coherence depends on the sensorimotor processing state before a steady force task and may thus increase after sensorimotor tuning to dynamic force generation. To test this hypothesis we instructed 16 human subjects to compensate static force after rest as well as after compensating predictable or unpredictable dynamic force with their right index finger. We calculated EEG-EMG coherence, cortical motor spectral power, and the motor performance during the force conditions. Corticospinal beta-coherence during stationary force was excessively elevated if the steadystate contraction was preceded by predictable dynamic force instead of rest, and was highest after unpredictable dynamic force. The beta-power decreased from rest to predictable dynamic force, and was lowest during unpredictable dynamic force. The increase in corticospinal beta-coherence showed a significant negative correlation with the preceding change in beta-power. The tuning to dynamic force did not entail an inferior motor performance during static force. The results imply a correlation between corticospinal beta-range coherence and the computational load of the preceding isometric motor engagement. We suggest beta-range coherence provides a functional corticospinal gateway for steady force-related processing that can override cortical states tuned to dynamic force. The modulation of corticospinal beta-range coherence might thus ensure comparable precision of static force in various motor contexts.

The strength of the corticospinal coherence depends on the predictability of modulated isometric forces

“…In a previous study (Omlor et al 2011), we showed that beta-range corticospinal coherence during isometric compensation of static force is highly dependent on the prestationary motor state: the beta-range CMC was higher after unpredictable frequency-and amplitude-modulated forces. These modulated forces induce higher computational load as reflected in the stronger cortical motor desynchronization (i.e., lower cortical motor spectral power) than predictable frequency-modulated forces.…”

“…Furthermore, on the basis of the lower cortical motor spectral power (SP) during UF described in Omlor et al (2011), we predicted stronger cortical motor desynchronization during UF, which would be reflected in smaller cortical motor SP. We also expected a stronger cortical activation, as measured by the task-related desynchronization (TRD) computed by the SP during the task with reference to a baseline (Pfurtscheller 1992;Pfurtscheller and Andrew 1999;Pfurtscheller and Aranibar 1977).…”

Improved Sensorimotor Performance via Stochastic Resonance

“…This is reflected in corticomuscular (EEG-MEG/EMG) coherence (Conway et al, 1995;Brown, 2000;Baker et al, 2006;Baker, 2007;Omlor et al, 2007Omlor et al, , 2011Mendez-Balbuena et al, 2012). Baker et al (2006) provided direct evidence that sustained afferent discharge from muscle receptors is coherent with central oscillations involved with sensorimotor processing.…”

Neuromagnetic investigations of mechanisms and effects of STN-DBS and medication in Parkinson's disease

“…For larger movements such as changes in length of muscles, angles of joints, the beta-CMC during the following rest phase was increased compared to after smaller movements (Witte et al, 2007). This pointed to a possible role of beta-CMC in re-calibration mechanisms Omlor et al, 2011). Increases in beta-CMC was also accompanied by improved compliance and decreased errors , which may suggest that increased beta-CMC improves integration of somatosensory information leading to better motor performance Witte et al, 2007;Omlor et al, 2011).…”

“…An experiment with varying motor tasks before a hold state showed that beta-CMC was modulated depending on the computational load of the preceding motor activity (Omlor et al, 2011). For larger movements such as changes in length of muscles, angles of joints, the beta-CMC during the following rest phase was increased compared to after smaller movements (Witte et al, 2007).…”