The effect of single and dual task training on the intracortical inhibition in young and old adults

Introduction It has been demonstrated that single-task (ST) balance training enhances performance in balancing alone, whereas dual-task (DT) balance training improves the ability to perform two tasks concurrently (Kiss et al., 2018). Previous research has also indicated that short-interval intracortical inhibition (SICI) is modulated in a task-specific manner following explosive or balance training (Taube et al., 2020). Based on these findings, the objective of this study was to investigate task-specific modulations of intracortical inhibition following ST or DT training in both young and older adults. Methods Participants were randomly separated into 2 different training groups (ST or DT) among their age (young or old). Young groups had 6 and old groups 9 balance training sessions within 3 weeks, the DT training consisted of cognitive and motor secondary tasks. Pre and post training, a balance task was performed on a rocker board in three different conditions: 1) balance only 2) balance + secondary motor (ball on a tray) and 3) balance + secondary cognitive (2-back). During the execution of these three conditions, SICI was measured with TMS by applying single pulse (120 % aMT) and double pulse stimulations (70 % + 120 % aMT) over the motor cortical area representing the right tibialis anterior muscle. Results Training improvements in balance performance trended to be condition-specific (p = .057). While the ST training groups only improved in the single balance task (5.2%), the DT training groups reduced the balance sway in all 3 conditions, but mostly in the dual motor condition (19.1%). Furthermore, there was a trend towards a time*age effect (p = .065), indicating improvements only in young participants (12.6% vs -0.1% in old).There was a significant fourfold interaction for SICI (p = .048), mainly indicating A) an upregulation in young (34.1%) and a downregulation in old (-33.9%) after the training and B) increased SICI after DT training in the dual motor condition (50.2%) and after ST training in single balance (21.7%). Discussion/Conclusion This study provides further evidence for task-specific adaptations after balance training, as ST training was beneficial for balancing alone and DT training in the dual motor task. This result is supported by the modulation of SICI. The changes were age-specific, with no improvements for the older groups. More interestingly, intracortical inhibition was upregulated in young and downregulated in old, indicating age-specific adaptations in SICI following a comparable training protocol. Based on the hypothesis that intracortical inhibition decreases during initial motor learning and increases in later stages, we hypothesize that a training duration of 3 weeks is sufficient to induce positive cortical modulation in young adults but not in older adults. References Kiss, R., Brueckner, D., & Muehlbauer, T. (2018). Effects of single compared to dual task practice on learning a dynamic balance task in young adults. Frontiers in Psychology, 9, 311. https://doi.org/10.3389/fpsyg.2018.00311 Taube, W., Gollhofer, A., & Lauber, B. (2020). Training‐, muscle‐ and task‐specific up‐ and downregulation of cortical inhibitory processes. European Journal of Neuroscience, 51(6), 1428–1440. https://doi.org/10.1111/ejn.14538

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