[Evoked motor potentials obtained with double magnetic cortical stimulation: techniques and interpretation]

Area of Science:

• Neuroscience
• Clinical Neurophysiology

Background:

• Motor evoked potentials (MEP) using single and double magnetic stimulation have advanced significantly.
• Double magnetic stimulation offers refined techniques for clinical neurophysiological assessments.

Purpose of the Study:

• To detail the techniques and parameters of double magnetic stimulation for clinical use.
• To investigate facilitatory and inhibitory influences within the motor system using double magnetic stimulation.

Main Methods:

• Employed a conditioning-test design to analyze muscular responses in the first dorsal interosseus muscle.
• Varied shock intensity, interstimulus interval (ISI), and conditioning coil location (ipsilateral motor cortex, contralateral motor cortex, contralateral cerebellum).

Main Results:

• Stimulation over the same cortical area revealed facilitation (ISI 1-3 ms) and inhibition (ISI 55-255 ms) at different intensities and ISIs.
• Interhemispheric stimulation (opposite hand area) showed initial facilitation (ISI 1-5 ms) followed by inhibition (up to ISI 30 ms).
• Cerebellar stimulation induced inhibition (ISI 5 ms) over the contralateral motor cortex.

Conclusions:

• Double magnetic stimulation over the same cortical area probes intrinsic motor strip circuitry and pyramidal tract influences.
• Stimulation of each motor area assesses interhemispheric communication via the corpus callosum.
• Cerebellar stimulation demonstrates inhibitory effects on the contralateral cerebral motor cortex.