Journal
CEREBRAL CORTEX
Volume 28, Issue 4, Pages 1502-1515Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/cercor/bhy016
Keywords
corticospinal; gain modulation; sensorimotor; state-dependent; transcranial magnetic stimulation
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Funding
- Graduate Training Centre of Neuroscience & International Max Planck Research School, Graduate School of Neural Information Processing
- Graduate School of Neural and Behavioral Sciences, Tuebingen, Germany
- Baden-Wuerttemberg Foundation [NEU005]
- German Federal Ministry of Education and Research [BMBF] [13GW0119B, 13GW0214B]
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Rhythmic synchronization of neurons is known to affect neuronal interactions. In the motor system, oscillatory power fluctuations modulate corticospinal excitability. However, previous research addressing phase-specific gain modulation in the motor system has resulted in contradictory findings. It remains unclear how many time windows of increased responsiveness each oscillatory cycle provides. Moreover, we still lack conclusive evidence as to whether the motor cortex entails an intrinsic response modulation along the rhythm cycle, as shown for spinal neurons. We investigated this question with single-pulse transcranial magnetic stimulation over the primary motor cortex at rest. Application of near-motor threshold stimuli revealed a frequency-and phase-specific gain modulation at both cortical and spinal level, independent of the spontaneous oscillatory power fluctuations at each level. We detected bilateral sensorimotor circuits in the lower beta-band (14-17 Hz) and unilateral corticospinal circuits in the upper beta-band (20-24 Hz). These findings provide novel evidence that intrinsic activity in the human motor cortex modulates input gain along the beta oscillatory cycle within distinct circuits. In accordance with periodic alternations of synchronous hyper- and depolarization, increased neuronal responsiveness occurred once per oscillatory beta cycle. This information may lead to new brain state-dependent and circuit-specific interventions for targeted neuromodulation.
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