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Power grip disinhibits the ipsilateral sensorimotor cortex: a TMS and fMRI study
Henrik Foltys1, Ingo G Meister, Jürgen Weidemann
1Department of Neurology, University of Aachen, Germany.
Neuroimage
|June 20, 2003
Summary
Forceful hand muscle activation (power grip) increases corticospinal system excitability, primarily via cortical mechanisms. This neurophysiological finding, observed using fMRI and TMS, reveals reduced sensorimotor cortex activation during concurrent tasks.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Electrophysiological studies indicate increased ipsilateral corticospinal system excitability during forceful hand muscle activation (power grip).
- The underlying mechanisms for this excitability increase were previously unclear, with potential spinal or cortical origins.
- Understanding the cortical contribution is crucial for interpreting neurophysiological findings related to motor tasks.
Purpose of the Study:
- To investigate the cortical mechanisms underlying increased ipsilateral corticospinal excitability during a power grip.
- To determine if functional magnetic resonance imaging (fMRI) can detect changes in sensorimotor cortex activation associated with this phenomenon.
- To explore the implications of these findings for interpreting neuroimaging data during motor tasks.
Main Methods:
- Transcranial Magnetic Stimulation (TMS) was used to assess corticospinal excitability by measuring stimulus-response curves.
- Functional Magnetic Resonance Imaging (fMRI) compared brain activation during repetitive hand movements with and without an accompanying contralateral power grip.
- Analysis focused on changes in sensorimotor cortex activation, specifically in the postcentral and precentral gyri.
Main Results:
- TMS confirmed increased ipsilateral corticospinal excitability during forceful hand maneuvers, evidenced by enhanced stimulus-response curves.
- fMRI revealed reduced movement-related activation in the ipsilateral sensorimotor cortex when a contralateral power grip was employed.
- Peak deactivation was observed in the left postcentral gyrus, extending into the precentral gyrus, indicating a specific cortical response.
Conclusions:
- Forceful hand muscle activation (power grip) at least partially mediates increased corticospinal excitability through cortical mechanisms.
- This phenomenon involves disinhibition within the ipsilateral sensorimotor cortex, leading to increased corticospinal system excitability.
- fMRI may show decreased hemodynamic responses in situations where other neurophysiological methods detect increased functional activity, highlighting the need for careful interpretation of imaging data.