TIME COURSE OF MOTOR SKILL MEMORY: ELECTROPHYSIOLOGICAL INSIGHTS

The brain is not idle during sleep but rather continues to process information obtained during prior wakefulness. Motor memory depends on both online and offline consolidation processes¹. Offline consolidation occurs during wakeful rest or sleep, without additional practice². During sleep, consolidation of motor skill memories is dependent on thalamo-cortical, hippocampal and striatal activity^3-4. Herein, using electrophysiology, we investigated the contribution of different brain structures to sleep-associated consolidation across time. Furthermore, we tested brain electrical activity associated with task generalization. The complete experiment encompassed an 11-day period, subsequent to several weeks of adaptation to the set-up and head-fixation. On days 1-4, head-fixed mice (C57BL/6J; 3-6 months, male) learned to perform on an accelerating complex-wheel (unevenly spaced rods), a task previously shown to be hippocampus-dependent⁵. Cortical and hippocampal local field potentials were recorded during task learning and during the subsequent 6 hours of sleep.
Learning was followed by a significant increase in sleep spindle density compared to baseline sleep. Interestingly, although this effect emerged early in the sleep period, it became more pronounced in later hours. This learning-related enhancement persisted across multiple post-learning days during slow-wave sleep. After a 5-day gap in learning, performance was re-tested (‘delayed memory test’) and sleep electrophysiology was measured. On the last day, generalization of the task was tested using a wheel with a novel, previously unseen, pattern of rods (‘transfer learning test’). Slow oscillation-spindle coupling was strongest during the sleep after transfer learning test.