Differential contribution of the supplementary motor area to stabilization of a procedural motor skill acquired through different practice schedules.

Behavioral studies have suggested that the stabilization of motor memory varies depending on the practice schedule. The neural substrates underlying this schedule-dependent difference in memory stabilization are not known. Here, we evaluated the effects of 1-Hz repetitive transcranial magnetic stimulation (rTMS) applied to different cortical regions and sham after one session of training (Day 1) of sequential motor skills acquired through blocked (each sequence was completely trained before training the next)-practice schedules and random (random training of 3 sequences)-practice schedules. The recall of sequences learned on Day 1 by Day 2 was measured in different groups of healthy volunteers. The rTMS over the supplementary motor area (SMA) but not over control regions or over the primary motor cortex (M1) immediately after practice or over SMA 6 h later reduced recall relative to sham only in the blocked-practice group. In contrast, recall in the random-practice group was unaffected by rTMS. These results document a differential contribution of the SMA to the stabilization of motor memories acquired through different practice schedules. More generally, they indicate that the anatomical substrates underlying motor-memory stabilization (or their temporal operation) do differ depending on the practice schedule.