title: Speed of processing in the primary motor cortex: a continuous theta burst stimulation study.
abstract: 'Temporally urgent' reactions are extremely rapid, spatially precise movements that are evoked following discrete stimuli. The involvement of primary motor cortex (M1) and its relationship to stimulus intensity in such reactions is not well understood. Continuous theta burst stimulation (cTBS) suppresses focal regions of the cortex and can assess the involvement of motor cortex in speed of processing. The primary objective of this study was to explore the involvement of M1 in speed of processing with respect to stimulus intensity. Thirteen healthy young adults participated in this experiment. Behavioral testing consisted of a simple button press using the index finger following median nerve stimulation of the opposite limb, at either high or low stimulus intensity. Reaction time was measured by the onset of electromyographic activity from the first dorsal interosseous (FDI) muscle of each limb. Participants completed a 30 min bout of behavioral testing prior to, and 15 min following, the delivery of cTBS to the motor cortical representation of the right FDI. The effect of cTBS on motor cortex was measured by recording the average of 30 motor evoked potentials (MEPs) just prior to, and 5 min following, cTBS. Paired t-tests revealed that, of thirteen participants, five demonstrated a significant attenuation, three demonstrated a significant facilitation and five demonstrated no significant change in MEP amplitude following cTBS. Of the group that demonstrated attenuated MEPs, there was a biologically significant interaction between stimulus intensity and effect of cTBS on reaction time and amplitude of muscle activation. This study demonstrates the variability of potential outcomes associated with the use of cTBS and further study on the mechanisms that underscore the methodology is required. Importantly, changes in motor cortical excitability may be an important determinant of speed of processing following high intensity stimulation.
authors.affiliation: Graduate Department of Rehabilitation Science, University of Toronto, Toronto, Ontario, Canada; Mobility Research Team, Toronto Rehab, Toronto, Ontario, Canada. Electronic address: Bimal.lakhani@utoronto.ca.
authors.forename: Bimal
authors.initials: B
authors.lastname: Lakhani
authors.affiliation: School of Psychology, Queens University Belfast, Belfast, Northern Ireland, United Kingdom.
authors.forename: David A E
authors.initials: DA
authors.lastname: Bolton
authors.affiliation: School of Psychology, Queens University Belfast, Belfast, Northern Ireland, United Kingdom.
authors.forename: Veronica
authors.initials: V
authors.lastname: Miyasike-Dasilva
authors.affiliation: Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada; Glenrose Rehabilitation Hospital, Alberta Health Services, Edmonton, Alberta, Canada.
authors.forename: Albert H
authors.initials: AH
authors.lastname: Vette
authors.affiliation: Graduate Department of Rehabilitation Science, University of Toronto, Toronto, Ontario, Canada; Mobility Research Team, Toronto Rehab, Toronto, Ontario, Canada; School of Psychology, Queens University Belfast, Belfast, Northern Ireland, United Kingdom.
authors.forename: William E
authors.initials: WE
authors.lastname: McIlroy
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D055592:Biophysical Phenomena / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Continuous theta burst stimulation; Motor control; Processing Speed; Reaction time; Transcranial magnetic stimulation