Thomas Gilbertson | PubMed Health

PubMed2006

Phasic increases in cortical beta activity are associated with alterations in sensory processing in the human.

Oscillatory activity in the beta (beta)-frequency band (13-35 Hz) can be recorded over the sensorimotor cortex in humans. It is coherent with electromyographic activity (EMG) during tonic contraction, but whether the cortical beta-oscillations are primarily motor or sensorimotor in function remains unclear. We tested the hypothesis that cortical beta-activity is associated with an up-regulation of sensory inputs that may be relevant to the organization of the motor response. We recorded cortical somatosensory potentials (SEPs) elicited by electrical stimuli to the median nerve at the wrist triggered by increases of electroencephalographic (EEG) beta-activity in the contralateral fronto-central EEG and compared these to SEPs presented at random intervals. The involvement of motor cortex in the triggering EEG activity was confirmed by a simultaneous elevation of cortico-spinal synchrony in the beta-band. The negative cortical evoked potential peaking at 20 ms and the positive evoked potential peaking at 30 ms after median nerve shocks were increased in size when elicited after phasic increases in beta-activity. The functional coupling of sensory and motor cortices in the beta-band was confirmed in recordings of electrocorticographic activity in two patients with chronic pain syndromes, suggesting a means by which beta-activity may simultaneously influence cortical sensory processing, motor output and promote sensory-motor interaction.

Adult↗

PubMed2005

Existing motor state is favored at the expense of new movement during 13-35 Hz oscillatory synchrony in the human corticospinal system.

Oscillations in local field potentials in the beta-frequency band (13-35 Hz) are a pervasive feature of human and nonhuman primate motor cortical areas. However, the function of such synchronous activity across populations of neurons remains unknown. Here, we test the hypothesis that beta activity may promote existing motor set and posture while compromising processing related to new movements. Three experiments were performed. First, healthy subjects were instructed to make reaction time movements of the outstretched index finger in response to imperative cues triggered by transient increases in corticospinal synchrony, as evidenced by phasic elevations of beta-frequency band microtremor and intermuscular synchrony. Second, healthy subjects were instructed to resist a stretch to the index finger triggered in the same way. Finger acceleration in the reaction time task and transcortical components of the stretch reflex were measured and compared with those elicited by random cue or stretch presentation. Finally, we sought a correlation between finger acceleration in the reaction time task and cortical synchrony directly measured from the electrocorticogram in two patients undergoing functional neurosurgery. We demonstrate that movements are slowed and transcortical responses to stretch are potentiated during periods of elevated beta-band cortical synchrony. The results suggest that physiological periods of beta synchrony are associated with a cortical state in which postural set is reinforced, but the speed of new movements impaired. The findings are of relevance to Parkinson's disease, in which subcortical and cortical beta-band synchronization is exaggerated in the setting of increased tone and slowed movements.

Adult↗