In the present study, however, we did not detect any practice-related changes in IHI. Methodological differences between our experiments and those of previous study could account for our different findings. In the present study we investigated changes in the IHI targeting the untrained motor cortex after a simple ballistic motor learning task, while previous studies examined different tasks, involving force production (Shim et al., 2005) selleck chemicals or motor sequence learning, i.e. the serial reaction time task (Perez et al., 2007; Camus et al., 2009).
It is therefore possible that the variable cognitive load or attentional demand involved in different forms of motor learning may influence the results. Additionally, the lack of change in IHI could be due to other specific features of the present experiment, such as the relatively short
duration of the motor task. In this regard it is worth noting that Hortobágyi et al. (2011) observed a less profound IHI after 1000 submaximal voluntary contractions of the FDI. Finally, an alternative hypothesis is that our results were influenced by the constant isometric force produced by the left hand during training, as volitional activity in one hand can modulate IHI in the homologous muscle of the contralateral limb (Giovannelli et al., 2009; Hinder et al., 2010). In theories of optimal Ipilimumab cost motor control (Todorov, 2004), the motor system attempts to achieve a desired level of performance at minimal cost. In the present experiments we might then speculate why motor training leads to reduced EMG mirroring, as it has no direct effect on the task itself, which is to increase acceleration of the opposite hand. One possible explanation is that it is a result of a very generalized ‘cost function’, which is to minimize all activity associated with the task, whether it is relevant or irrelevant to task performance. Effectively this would reduce all overflow of activity that was not relevant to the task. Another explanation is that reduced EMG mirroring is secondary to
the motor system’s attempts to maximize some other, task-relevant, function, such as focussing the motor command onto only those motor outputs that are strictly required to produce the required movement. The present study specifically examined the effects of brief motor practice on EMG mirroring, and therefore we do not know the extent to which the HSP90 effects would carry over to other stages of motor learning, such as consolidation (Brashers-Krug et al., 1996; Muellbacher et al., 2002) or long-term retention (Reis et al., 2009), or whether practice-related changes of EMG mirroring in one hand are associated with similar changes in the untrained as well as in the trained hand, a phenomenon referred to as intermanual transfer (Perez et al., 2007; Camus et al., 2009). It is also important to note that in the present study we adopted a simple, ballistic movement of the finger with no real requirements for accuracy, just acceleration.