A SPATIOTEMPORAL DIPOLE MODEL OF THE READINESS POTENTIAL IN HUMANS .2. FOOT MOVEMENT

Readiness potentials (RP) have been recorded in 9 subjects who performed voluntary unilateral plantar flexions with the right or left foot. These show a paradoxical ipsilateral dominance. Spatio-temporal dipole models were obtained for these data, by iterative parameter estimation. The non-uniqueness of the inverse problem leads to several models which describe the data almost equally well, and which all pass orthogonality tests for the individual residuals and source waves. In these dipole models the ipsilateral preponderance is attributed to generators in the contralateral hemisphere, which agrees with results from MEG recording. According to these models the main generators of the RP are in the primary motor cortex, one bilaterally in its posterior wall and the other in the contralateral crown. This agrees with earlier results for finger RPs. However, for foot RPs, it was difficult to distinguish individual sub-components in both the observed scalp potentials and the estimated temporal activation patterns of the dipoles. Some of the presented models include a fronto-central dipole which possibly represents activity of the supplementary motor area. It is concluded that this finding is at best suggestive and needs further investigation.