The French study involved 32 healthy volunteers. They were between the ages of 20 and 35 years.
The volunteers were trained to perform a computerized finger-tapping task. First they memorized a sequence of eight finger movements.
Then they repeatedly tapped the sequence on a computer keyboard during 30-second periods. The goal was to be as fast and accurate as possible.
The authors reported that previous studies have used this task to show delayed gains in performance after a night of sleep. As a result some researchers recommend that physical practice should be followed by sleep to enhance a newly learned motor skill.
For this study some volunteers physically practiced the finger sequence. Others practiced it using motor imagery, a form of mental practice.
These participants only simulated the action in their mind. They perceived the sensations of how it feels to perform the action. But they didn’t practice the actual finger movements.
Performance was tested right after the 8 p.m. training session. It was retested at 8 a.m. after practice and an eight-hour night of sleep.
As a control, one group was tested after motor imagery practice and no sleep. They were trained at 8 a.m. and retested the same day at 8 p.m.
Results show “offline gains” in performance after a night of sleep for both practice groups. Their speed and accuracy improved. In contrast, the “no sleep” group was slower and made more errors during the retest session.
The results indicate that sleep contributes to the consolidation of motor learning acquired through motor imagery. They also support the principle of “functional equivalence” between mental practice and physical practice.
The authors suggest that motor imagery practice could be included during physical therapy and rehabilitation. For the maximum benefit this practice should be performed before a period of sleep.