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Magnetic brain stimulation
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1992
Year
Magnetic Brain StimulationMotor ControlPmsp DurationPeripheral Nervous SystemSocial SciencesStimulation DeviceKinesiologyNeurologyNeurological FunctionMagnetic MotorHealth SciencesEmg Silent PeriodTranscranial StimulationNeurostimulationBrain StimulationNervous SystemDeep Brain StimulationNeurophysiologyNeuroanatomyElectromyographyNeuroscienceCentral Nervous System
Later portions of the post‑EMP silent period are mainly caused by stimulus‑related cerebral inhibitory or suppressing phenomena. The study examined the post‑EMP silent period in 25 healthy subjects, showing that early portions are driven mainly by segmental inhibitory loops from muscle twitches and descending cortical projections to alpha‑motoneurons, with possible intracortical inhibition contributing later. The post‑EMP silent period lengthened proportionally with stimulus intensity, was longer in hand and forearm muscles than in the upper arm, exceeded the peripheral silent period even when peripheral stimuli matched MEP force, could be elicited by weak magnetic stimuli without MEPs, and involved transient inhibition of spinal alpha‑motoneurons that recovered later, with only slight inhibition of cortical MEPs during the late silent period.
In 25 normal subjects, we studied the EMG silent period following the magnetic motor evoked potential (MEP) when the target muscle was tonically contracted (post-EMP silent period [PMSP]). In the first dorsal interosseous muscle (FDI), PMSP duration increased in linear proportion to stimulus intensity, but not to the size of the preceding MEP. The PMSP was longer in hand and forearm muscles than in upper arm muscles. In the FDI, PMSP was longer than the peripheral silent period (PSP) even when multiple peripheral stimuli were used to get M responses whose twitch force was equivalent to that of MEPs. Weak magnetic stimuli evoked silent periods preceded by no MEP in several subjects. Spinal alpha-motoneurons (alpha-MNs) were partially inhibited during the first PMSP portion, but later this effect recovered. MEPs due to weak electrical stimuli to motor cortex were only slightly inhibited during the late PMSP. Segmental inhibitory loops evoked by the muscle twitch and inhibitory projections descending to alpha-MNs from the cortex predominantly underlie earlier PMSP portions, but recurrent intracortical inhibition may also contribute. Later portions are predominantly due to other stimulus-related cerebral inhibitory or suppressing phenomena.