Author Identifier (ORCID)
Liam C. Tapsell: https://orcid.org/0000-0002-8052-196X
Christopher Latella: https://orcid.org/0000-0002-5857-9671
Anthony J. Blazevich: https://orcid.org/0000-0003-1664-1614
Janet L. Taylor: https://orcid.org/0000-0001-8976-5162
Abstract
Interhemispheric inhibition (IHI) acts between hemispheres to decrease motor cortical excitability. IHI changes during movement preparation, but it is unknown whether altering IHI, independent of other factors, alters movement initiation. For the index finger abductor muscle (first dorsal interosseous; FDI), IHI is weaker during contralateral index abduction than adduction. Thus, this study aimed to modulate IHI through contralateral contraction and measure resultant changes in reaction time. Fifteen healthy participants (age 19–39 years) completed a reaction-time task requiring brief left index finger abduction. Prior to reactions, participants started either a sustained isometric abduction or adduction contraction of the right index finger. Single- or paired-pulse transcranial magnetic stimulation (TMS) elicited motor evoked potentials (MEPs) from left FDI in the late pre-movement phase. For each contralateral contraction direction, unconditioned and conditioned MEPs (preceded by suprathreshold TMS over the other hemisphere at 10 or 40 ms) were recorded. Conditioned MEPs, expressed relative to unconditioned MEPs, provided measures of short-interval IHI (SIHI) and long-interval IHI (LIHI). Left index finger reaction time was also measured. Linear mixed models showed that reaction time was 9 ± 9 ms (6%) slower during right adduction than abduction (F1,1875 = 30.7, p < 0.001). Unconditioned MEPs in left FDI were 1.1 ± 2.0 mV (37%) smaller (F1,270 = 8.82, p = 0.003) and SIHI 11 ± 16% stronger during right adduction (F1,279 = 15.15, p < 0.001). However, LIHI was not different between right contraction conditions (F1,272 = 0.410, p = 0.522). These results suggest that IHI can alter reaction time by influencing corticospinal excitability. Stronger SIHI during right adduction likely delayed pre-movement increases in corticospinal excitability, slowing reaction time.
Document Type
Journal Article
Date of Publication
12-1-2025
Volume
243
Issue
12
PubMed ID
41160222
Publication Title
Experimental Brain Research
Publisher
Springer
School
Nutrition and Health Innovation Research Institute / Centre for Precision Health / School of Medical and Health Sciences
RAS ID
84587
Funders
Australian Government Research Training Program
Creative Commons License
This work is licensed under a Creative Commons Attribution-No Derivative Works 4.0 License.
Comments
This is an Author's Accepted Manuscript of: Tapsell, L. C., Latella, C., Blazevich, A. J., & Taylor, J. L. (2025). Interhemispheric inhibition modifies reaction time of the index finger. Experimental Brain Research, 243. https://doi.org/10.1007/s00221-025-07182-w
This version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.1007/s00221-025-07182-w