Internally driven vs. externally cued movement selection: a study on the timing of brain activity

Brain imaging studies in man and single cell recordings in monkey have sugg ested that medial supplementary motor areas (SMA) and lateral pre-motor are as (PMA) are functionally dissociated concerning their involvement in inter nally driven and externally cued movements. This dichotomy, however, seems to be relative rather than absolute. Here, we searched for further evidence of relative differences and aimed to determine by what aspect of brain act ivity (duration, strength, or both) these might be accounted for. Event-rel ated potentials (ERPs) were recorded while healthy, right-handed subjects s elected one of three possible right hand digit movements based either on 'i nternal' choice or 'external' cues. The results obtained from ERP mapping s uggest that movement selection evokes the same electrical brain activity pa tterns in terms of surface potential configurations in the same order and a t the same strength independent of the selection mode. These identical conf igurations, however, differed in their duration. Combined with the results of a distributed source localization procedure, our data are suggestive of longer lasting activity in SMA during the 'internal' and longer lasting act ivity in PMA during the 'external' condition. Our results confirm previous findings in showing that SMA and PMA are distinctively involved in the two tasks and that this functional dichotomy is relative rather than absolute b ut indicate that such a dissociation can result from differences in duratio n rather than pure strength of activation. (C) 2000 Elsevier Science B.V. A ll rights reserved.