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

Introduction The evidence for changes in intracortical inhibition when executing two tasks simultaneously (i.e., dual tasking) is ambiguous as decreased (Corp et al., 2014) and increased (Corp et al., 2016) inhibition were reported. One way to bring more light into this question is to tests the effect of a single task training (STT) and a dual task training (DTT) on the short interval intracortical inhibition (SICI) during a single balancing task and two different dual tasks in healthy young adults. Methods Twenty-nine healthy young adults were randomly separated into two groups participating in STT (n = 15) or DTT (n = 14) consisting of 6 training sessions within 3 weeks. Before and after the training, a single task (balancing on a rocker board) was performed at two resistance levels (easy and hard). Additionally to the single task, either a cognitive (2-back number recall) or a motor (balancing a ball on a hand-held tray) dual task was executed simultaneously. During execution of these three tasks, SICI was measured with transcranial magnetic stimulation over the motor cortical area representing the right tibialis anterior. Results Training improvements in balance performance were group and task-specific over time (p = .018). While the STT group improved more in the single balance task (12.3% vs. 6.6% DTT), the DTT group had more sway reductions in the motor dual task condition (13.7% vs. 4.5% STT). Similar statistical outcome (p = .034) was observed for the dual task costs (DTC). There was a tendence for SICI (p = .075), mainly indicating higher increase in SICI for the DTT group in the motor dual task (16.0% vs. 5.8% STT). During the execution of the single balance task, the group-specific adaptations in SICI were less pronounced (13.7% DTT vs. 16.2% STT). When analyzing the SICI dual task difference (Δ) from single to dual task, SICI is altered group and task specific (p = .011). The DTT group could increase the dual task difference in SICI in the dual motor condition (Δ 3.2%), whereas the STT group had a decrease (Δ -9.6%). Discussion/Conclusion The results of this study show that DTT causes gains in balance performance and increases in SICI when the secondary task is also a motor task, but not when the second task is a cognitive one. STT is particularly beneficial in the single task. It is therefore assumed that intracortical inhibition is important during the simultaneous performance of two motor tasks, while intracortical inhibition was not modulated in a group-specific manner by the additional cognitive task. References Corp, D. T., Lum, J. A. G., Tooley, G. A., & Pearce, A. J. (2014). Corticospinal activity during dual tasking: A systematic review and meta-analysis of TMS literature from 1995 to 2013. Neuroscience & Biobehavioral Reviews, 43, 74-87. https://doi.org/10.1016/j.neubiorev.2014.03.017 Corp, D. T., Rogers, M. A., Youssef, G. J., & Pearce, A. J. (2016). The effect of dual-task difficulty on the inhibition of the motor cortex. Experimental Brain Research, 234, 443-452. https://doi.org/10.1007/s00221-015-4479-2

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