title: Corticospinal excitability is reduced in a simple reaction time task requiring complex timing.
abstract: Increasing the complexity of a movement has been shown to result in longer simple reaction time (RT), which has been attributed to sequencing or timing requirements following the go-signal. However, RT differences may also be due to differences in corticospinal excitability (CE) as previous studies have found an enhanced excitatory state of corticospinal neurons in complex tasks. Transcranial magnetic stimulation (TMS) was used in the present study to probe the excitability of the motor pathway during the simple RT interval for single (simple) versus multiple (complex) key press responses. Premotor RT data indicated that participants responded significantly (p<.001) faster in the simple task compared to the complex task, confirming response complexity was manipulated appropriately. Analysis of the CE data indicated that motor evoked potential (MEP) amplitudes increased with time following the go-signal in both conditions and that MEP amplitudes in the simple task were significantly larger than those in the complex task when evoked within 75ms of movement onset (p=.009). These findings suggest that the rate of increase for initiation-related neural activation is reduced for complex as compared to simple movements, which may partially explain differences in RT.
authors.affiliation: School of Health and Exercise Sciences, University of British Columbia, 1147 Research Road, Kelowna, British Columbia, Canada V1V 1V7.
authors.forename: Michael
authors.initials: M
authors.lastname: Kennefick
authors.affiliation: Department of Kinesiology, Langara College, 100 W 49th Ave, Vancouver, British Columbia, Canada V5Y 2Z6; School of Kinesiology, University of British Columbia, 6081 University Blvd, Vancouver, British Columbia, Canada V6T 1Z1.
authors.forename: Dana
authors.initials: D
authors.lastname: Maslovat
authors.affiliation: School of Kinesiology, University of British Columbia, 6081 University Blvd, Vancouver, British Columbia, Canada V6T 1Z1.
authors.forename: Romeo
authors.initials: R
authors.lastname: Chua
authors.affiliation: School of Human Kinetics, University of Ottawa, 125 University Private, Ottawa, Ontario, Canada K1N 6N5. Electronic address: tony.carlsen@uottawa.ca.
authors.forename: Anthony N
authors.initials: AN
authors.lastname: Carlsen
mesh_terms: D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D000071080:Cortical Excitability; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D005385:Fingers / Q000294:innervation / Q000502:physiology; D006801:Humans; D008297:Male; D009043:Motor Activity; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D011597:Psychomotor Performance; D011712:Pyramidal Tracts / Q000502:physiology*; D011930:Reaction Time; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Neural activation; Response complexity; Transcranial magnetic stimulation