"Micro-offline gains" convey no benefit for motor skill learning

Abstract

While practising a new motor skill, resting for a few seconds can improve performance immediately after the rest. This improvement has been interpreted as rapid offline learning1,2 ("micro-offline gains", MOG), supported by neural replay of the trained movement sequence during rest3. Here, we provide evidence that MOG reflect transient performance benefits, partially mediated by motor planning, and not replay-mediated offline learning. In five experiments, participants trained to produce a sequence of finger movements as many times as possible during fixed-duration practice periods. When participants trained during 10-second practice periods, each followed by a 10-second rest period, they produced more correct keypresses during training than participants who trained without taking breaks. However, this benefit vanished within seconds after the end of training, when both groups performed under comparable conditions, revealing similar levels of skill acquisition. This challenges the idea that MOG reflect offline learning, which, if present, should result in sustained performance benefits, compared to training without breaks. Furthermore, sequence-specific replay was not necessary for MOG, given that we observed persistent MOG when participants produced random sequences that never repeated, preventing any effect of (sequence-specific) replay on the performance. Importantly, we observed diminished MOG when participants could not pre-plan the first few movements of an upcoming practice period. We conclude that "micro-offline gains" represent short-lived performance benefits that are partially driven by motor pre-planning, rather than replay-mediated offline learning.