Body schema and tool specificity: A TMS study of expert and novice tennis players during mental rehearsal

Temporary modifications of body schema through the use of tools have been reported in patients with neglect and extinction. Moreover, neuroimaging data indicate that the neural substrates underlying motor control and motor imagery largely overlap in both patient and neurologically healthy populations. Using neurologically healthy athletes, the current research explored whether the long-term use of a tool leads to a modification of the body schema which is specific to that tool. Single pulse TMS applied over the left primary motor cortex was used to measure corticospinal excitability in contralateral forearm (extensor indicis proprius, EIP) and hand (first dorsal interosseous, FDI) muscles of expert and novice tennis players while they mentally practiced action in three sports: tennis forehand, table tennis forehand, golf drive. The critical instruction was to imagine the tool (racket, paddle, or club) was integrated with, and an extension of, the hand. Participants reported no difficulty performing their motor imagery. Analysis of corticospinal excitability indicated that the mental representation of specific muscles was selectively influenced by long-term experience with a specific tool. In expert tennis players, both the hand and forearm showed increased corticospinal facilitation during motor imagery of tennis but not golf or table tennis. In contrast to the measure of corticospinal excitability, the subjective data of experts indicated that the imagery experienced during tennis and table tennis were similar, possibly reflecting the similarity of the tools or the action (forehand swing). However, the objective measure of excitability and the subjective feedback converged on the assessment of no difference between golf and table tennis. Novice tennis players, although also athletic, show no modulation across sports. Further, the failure to find differences coincided with a dearth of significant differences in the subjective feedback. The analyses comparing groups indicated expert-novice differences in the tennis condition only, in both muscles. The consistent finding that between group differences were present only in the tennis condition agreed with the non parametric analyses of the subjective feedback. Two significant between group differences were found, both for the tennis condition feedback: experts agreed more than novices that they 'had the sensation that the racket was an extension of the hand' and experts considered it easier than novices 'to imagine the physical sensation' (i.e. kinesthetic imagery) during imagery of tennis. In conclusion, the analyses of corticospinal excitability indicated that the mental representation of specific muscles was selectively influenced by long-term experience with a specific tool