title: Different Stimulation Frequencies Alter Synchronous Fluctuations in Motor Evoked Potential Amplitude of Intrinsic Hand Muscles-a TMS Study.
abstract: The amplitude of motor-evoked potentials (MEPs) elicited with transcranial magnetic stimulation (TMS) varies from trial-to-trial. Synchronous oscillations in cortical neuronal excitability contribute to this variability, however it is not known how different frequencies of stimulation influence MEP variability, and whether these oscillations are rhythmic or aperiodic. We stimulated the motor cortex with TMS at different regular (i.e., rhythmic) rates, and compared this with pseudo-random (aperiodic) timing. In 18 subjects, TMS was applied at three regular frequencies (0.05 Hz, 0.2 Hz, 1 Hz) and one aperiodic frequency (mean 0.2 Hz). MEPs (n = 50) were recorded from three intrinsic hand muscles of the left hand with different functional and anatomical relations. MEP amplitude correlation was highest for the functionally related muscle pair, less for the anatomically related muscle pair and least for the functionally- and anatomically-unrelated muscle pair. MEP correlations were greatest with 1 Hz, and least for stimulation at 0.05 Hz. Corticospinal neuron synchrony is higher with shorter TMS intervals. Further, corticospinal neuron synchrony is similar irrespective of whether the stimulation is periodic or aperiodic. These findings suggest TMS frequency is a crucial consideration for studies using TMS to probe correlated activity between muscle pairs.
authors.affiliation: Queensland Brain Institute, The University of Queensland St Lucia, QLD, Australia.
authors.forename: Martin V
authors.initials: MV
authors.lastname: Sale
authors.affiliation: Brain and Mental Health Laboratory, School of Psychological Science and Monash Biomedical Imaging, Monash Institute of Cognitive and Clinical Neuroscience, Monash University Melbourne, VIC, Australia.
authors.forename: Nigel C
authors.initials: NC
authors.lastname: Rogasch
authors.affiliation: Discipline of Physiology, School of Medical Sciences, The University of Adelaide Adelaide, SA, Australia.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Nordstrom
keywords: abductor digiti minimi; abductor pollicis brevis; cortical oscillations; first dorsal interosseous; motor cortex; motor-evoked potential; transcranial magnetic stimulation