Early stages of motor skill learning and the specific relevance of the cortical motor system - a combined behavioural training and theta burst TMS study

Purpose: To examine whether motor performance and motor learning in healthy subjects can be segregated into a number of distinct motor abilities which are linked to intact processing in different motor-related brain regions (M1, S1, SMA, PMC) early during learning. Methods: Seven young healthy subjects trained in eight motor arm tasks (Arm Ability Training, AAT) once a day for 5 days using their left non-dominant arm. Except for day 1 (baseline), training was performed before and after applying an inhibitory form of repetitive transcranial magnetic stimulation (cTBS, continuous theta burst) to either M1, S1, SMA, or PMC. Results: A principal component analysis of the motor behaviour data suggested four independent motor abilities: aiming, speed, steadiness, and visuomotor tracking. AAT induced substantial motor learning across abilities. Within session effects of cTBS revealed that activity in primary somatosensory cortex (S1) was relevant for motor performance and learning across all tasks whereas M1 was specifically involved in rapid tapping movements, PMC in ballistic arm navigation in extra-personal space; performance on a non-trained motor tasks was not affected by cTBS. Conclusions: Cortical sensory and motor areas including S1, M1, and PMC functionally contribute to early motor learning in a differential manner across motor abilities.