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Corticospinal Excitability Modulation During Action Observation
Published on: December 31, 2013
Motor cortex excitability changes preceding voluntary muscle activity in simple reaction time task.
M Nikolova1, N Pondev, L Christova
1Institute of Biophysics, Bulgarian Academy of Sciences, Acad G Bontchev Str, Bldg 21, Sofia, Bulgaria.
European Journal of Applied Physiology
|August 26, 2006
Summary
Transcranial magnetic stimulation (TMS) influences motor cortex excitability before movement. Specific TMS patterns, like single pulses, enhance motor evoked potentials (MEPs) earlier, while paired pulses show different effects, impacting reaction time (RT).
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Understanding motor cortex excitability is crucial for brain-computer interfaces and rehabilitation.
- Transcranial magnetic stimulation (TMS) offers a non-invasive method to probe cortical excitability.
- Reaction time (RT) is influenced by the complex neural processes preceding voluntary movement.
Purpose of the Study:
- To investigate the effects of single and paired-pulse TMS on motor cortex excitability during the premovement period.
- To analyze how different TMS parameters (interstimulus intervals) modulate motor evoked potentials (MEPs) and influence reaction time (RT).
- To explore the dynamic changes in cortical excitability preceding voluntary muscle activation.
Main Methods:
- Single and paired-pulse TMS applied to the left motor cortex in response to a visual cue.
- Recording motor evoked potentials (MEPs) from the first dorsal interosseous (FDI) muscle of the right hand.
- Varying interstimulus intervals (ISIs) of 3 ms and 13 ms for paired-pulse TMS.
- Analyzing MEPs at different delays relative to the onset of voluntary electromyographical (EMG) activity.
Main Results:
- MEPs gradually increased in the premovement period, with a strong augmentation 90-100 ms before EMG onset using single-pulse TMS.
- Paired-pulse TMS (13 ms ISI) showed smaller MEP augmentation that started earlier, with no clear gradual increase.
- Intracortical inhibition (ICI) was observed at 3 ms ISI only when TMS preceded EMG by >60 ms; shorter intervals showed MEP augmentation.
- A distinct 'dead band' period with no MEPs occurred 30-50 ms before voluntary EMG onset.
- MEP augmentation was generally more pronounced with single-pulse TMS.
Conclusions:
- The observed effects are likely due to the interplay of intracortical facilitation (ICF) and ICI, with distinct dynamic behaviors.
- Different TMS parameters and timing relative to movement onset reveal complex modulations of motor cortex excitability.
- These findings provide a more nuanced understanding of TMS's subtle influence on reaction time and motor preparation.
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