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Cortical modulation of spinal excitability: an F-wave study
B Mercuri1, E M Wassermann, P Manganotti
1Medical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892-1428, USA.
Electroencephalography and Clinical Neurophysiology
|February 1, 1996
Summary
Subthreshold transcranial magnetic stimulation modulates F-waves, reflecting spinal cord excitability. These F-wave changes, particularly in hand muscles, indicate the potential for probing spinal cord states using this technique.
Area of Science:
- Neuroscience
- Motor Control
- Electrophysiology
Background:
- F-waves are sensitive indicators of spinal cord excitatory states.
- Transcranial magnetic stimulation (TMS) can modulate neural pathways.
Purpose of the Study:
- To investigate the effects of subthreshold TMS on F-waves in hand and foot muscles.
- To explore the relationship between TMS timing and F-wave modulation.
Main Methods:
- Evoked F-waves in abductor pollicis brevis (hand) and extensor digitorum brevis (foot) muscles.
- Applied subthreshold TMS with varying delays relative to expected collision times.
- Analyzed F-wave latency, amplitude, and presence of facilitation/inhibition.
Main Results:
- Significant F-wave enhancement observed in the hand muscle at specific TMS delays, followed by inhibition.
- A secondary facilitatory phase and later enhancement peaks were noted in hand muscles.
- In the foot muscle, facilitation occurred earlier than expected, and inhibition was less pronounced.
Conclusions:
- Sequential arrival of cortical I-waves likely explains F-wave modulation in hand muscles.
- Anatomical and technical factors may influence F-wave responses in foot muscles.
- F-waves serve as a valuable probe for assessing dynamic changes in spinal cord excitability.