MENTAL REPRESENTATIONS OF MOVEMENTS - BRAIN POTENTIALS ASSOCIATED WITH IMAGINATION OF HAND MOVEMENTS

The present study was designed in order to contribute towards the unde rstanding of the physiology of motor imagery. DC potentials were recor ded when subjects either imagined or executed a sequence of unilateral or bilateral hand movements. The sequence consisted of hand movements in 4 directions, forwards, backwards, to the right and to the left, a nd varied from trial to trial. The sequence had been cued by visual ta rgets on a computer screen and had to be memorized before the trial wa s initiated. Changes of DC potentials between task execution and imagi nation were localized in central recordings (C3, Cz, C4) with larger a mplitudes when executing the task than when imagining to do so. Stimul ation of peripheral receptors associated with task execution or a diff erent level of activation of the cortico-motoneural system could accou nt for this finding. The main result of the present study was that wit h unilateral performance, the side of the performing hand (right, left ) had localized effects in recordings over the sensorimotor hand area (C3, C4) which were qualitatively the same with imagination and execut ion and quantitatively similar (i.e., without significant difference). Performance of the right hand augmented negative DC potentials in C3, performance of the left hand augmented amplitudes in C4. This result is consistent with the assumption that the primary motor cortex is act ive with motor imagery. Finally, the question has been addressed wheth er motor imagery may involve the left hemisphere to a larger extent th an the execution of the movement. It is shown that a particular contri bution of the left hemisphere associated with motor imagery may only s how up under strictly controlled conditions.