Effects of Sleep on Gross Motor Sequence Learning by Motor Imagery

Introduction:
Motor imagery (MI) involves mental imagery of movements without actually performing them and is known to improve motor learning. However, the role of sleep in motor sequence learning by MI remains unclear. Therefore, we are currently investigating the relationship between objective sleep indices and their effect on the consolidation of new gross motor sequences following MI.
Method:
27 healthy subjects (Mage = 21.48 years, 11 males) participated in a seven-day experimental schedule, including two nights of ambulatory polysomnography recordings. Participants visited the laboratory three times, starting either in the morning (AM-group) or evening (PM-group), with an 11-12-hrs retention interval between the visits. After learning an eight-step foot sequence they subsequently either had to mentally rehears the sequence for 12 blocks of 45 seconds (MI condition) or they had to listen to an audiobook (control condition) while EEG activity was recorded. We assessed performance of the foot sequence before (pre-test) and after (post-test 1) MI/audiobook, and during the two subsequent visits (post-test 2 and 3). Performance change was measured as the percentage change in the number of correct steps during the three post-tests (1-3) relative to the pre-test.
Results:
Only for the MI condition, we found a significant difference in performance during post-tests between the AM- and the PM-group (F(2, 44) = 5.108, p = .010). Subjects who trained in the evening (PM-group) showed a greater performance gain during post-test 2 (t = 2.175, p = .041) and post-test 3 (t = 2.562; p = .018) than those who trained in the morning (AM-group). Furthermore, subjects of the PM-group increased their performance significantly from before (post-test 2) to after sleep (post-test 3; t = 2.119; p = .046).
Conclusion:
Our preliminary results suggest that MI appears to be more effective in improving physical performance when performed in the evening than in the morning. Interestingly, a period of sleep following MI further improved gross-motor performance compared to wakefulness. Taken together, these findings highlight the potential role of post-training sleep for MI. Upcoming analyses of polysomnography data will help us to understand the possible effects of sleep on motor sequence learning after MI.