Dissecting motor skill acquisition: Spatial coordinates take precedence

Abstract

Practicing a previously unknown motor sequence often leads to the consolidation of motor chunks, which enable its accurate execution at increasing speeds. Recent imaging studies suggest the function of these structures to be more related to the encoding, storage, and retrieval of sequences rather than their sole execution. We found that optimal motor skill acquisition prioritizes the storage of the spatial features of the sequence in memory over its rapid execution early in training, as proposed by Hikosaka in 1999. This process, seemingly diminished in older adults, was partially restored by anodal transcranial direct current stimulation over the motor cortex, as shown by a sharp improvement in accuracy and an earlier yet gradual emergence of motor chunks. These results suggest that the emergence of motor chunks is preceded by the storage of the sequence in memory but is not its direct consequence; rather, these structures depend on, and result from, motor practice.

LTP-like noninvasive striatal brain stimulation enhances striatal activity and motor skill learning in humans

“…Furthermore, striatal tTIS led to behavioral effects by increasing training gains during a motor learning task. The behavioral effect was particularly pronounced in older participants, who have lower motor learning capacity 29,30 and less well-tuned underlying brain networks than younger participants 31,32 . In this work, we demonstrate that tTIS can overcome the depth-focality tradeoff observed in conventional NIBS techniques in humans, leading to sufficient current strengths to induce specific, focal and functionally relevant modulation of brain activity in deep brain structures such as the striatum.…”

“…In a second experiment, we validated the striatal LTP-like tTIS approach in a behavioral experiment by recruiting a cohort of older adults (N=15, right-handed, 9 females, average age 66.00±4.61 years), who often demonstrate diminished performance gains in motor learning tasks 29,30 , have less tuned underlying brain networks 31,32 and may have higher sensitivity to plasticity-modulating NIBS protocols 29,33 . Additionally, a new cohort of young healthy control subjects (N=15, right-handed, 8 females, average age 26.67±4.27 years) was recruited.…”

“…The pronounced response to the present intervention in the older participants can be explained by several potential reasons. One simple explanation is that healthy older adults show more room for improvement with striatal stimulation than young adults since healthy older adults show decreased performance levels and motor learning abilities 29,30 . Another possible explanation is based on previous imaging studies, which suggest suboptimal processing across dedicated brain networks during motor learning in older adults 41,42 .…”

“…Moreover, aging is related to structural and functional neurodegeneration and reduced brain plasticity, which are in turn associated with functional impairment 43,44 . Improving brain plasticity in regions affected by aging-related changes might result in restoring "natural" dynamics, ultimately leading to behavioral improvements 29 . In line with this hypothesis, previous studies on neurological disorders also found stronger NIBS effects in patients showing stronger dysfunction and impairment 45 .…”

“…The overall duration of the training and stimulation was approximately three times shorter than that in Experiment 1. This difference was introduced to adapt the protocol for follow-up studies recruiting patient cohorts and to homogenize the protocol with protocols considered in previous studies 22,29 . The analysis of the training phase indicated significant effects of the block (F(6, 351)=30.16, p<0.001, pη 2 =0.…”