Gray matter (GM) changes have been described after short learning tasks that lasted for 7 days or after external stimulation that lasted for 5 days. However, the early time course of training-dependent GM changes is still unknown. We investigated whether shorter motor training sessions (four times of 30 min training) would induce GM changes. Therefore, T1-weighted MRIs were acquired daily. Because reported GM changes were induced by learning, a close relationship was assumed between the functional activity and the GM changes. Therefore, fMRI was performed in addition to daily T1-weighted MRIs. At the end of the four training sessions (at time point "post"), the test results of the trained motor skill were associated with an increase of GM in secondary cortical motor areas (dPMC(right), dPMC(left), SMA(left) and the right inferior parietal lobule, IPL(right)). The earliest time point at which a GM change was detected was 1day before in the right ventral striatum (by contrasting daily T1-weighted MRI vs. baseline). To analyze whether this very early GM change within the right ventral striatum is associated with those GM changes at time point post (which were associated with motor skill performance), their functional connectivity was investigated over the time period of motor skill training. This analysis revealed an increase of functional coupling between these regions (striatum and cortex) over the training days. The current data demonstrate training-induced short GM plasticity is paralleled by their temporally dynamical process of functional interaction between the cortex and the striatum in response to a motor skill training.
