Top-down modulation of brain activity underlying intentional action and its relationship with awareness of intention: an ERP/Laplacian analysis

Intentional actions are executed with the peculiar experience of "I decide to do that." It has been proposed that intentional actions involve a specific brain network involving the supplementary motor areas (SMAs). Here, we manipulated the internal representation participants attended to (intention vs. movement) in order to (1) examine the activity of SMAs and of the primary motor cortex (M1) during intentional action preparation and execution, and (2) investigate the temporal relationship between activity in these structures and intention awareness. Participants performed self-paced key presses. After each key press, participants were asked to report either the time they had the first intention to press the key (W-condition) or the time they actually started the movement (M-condition). We then estimated surface Laplacians from brain electrical potentials recorded while participants were performing the task. Activity in SMAs was greater in the W-condition than in the M-condition more than 1 s before electromyographic (EMG) activation, suggesting that this region is indeed associated to the formation of conscious intention. Conversely, activity in primary motor cortex (M1) contralateral to the responding hand was larger in the M-condition than in the W-condition, revealing that this region is also modulated by top-down processes. In addition, waveforms time-locked to the W-judgement revealed that M1 as well as EMG activation preceded the time at which participants become aware of their intention by about 0.3 s. This observation argues against the possibility that the temporal delay between motor-related activation and intention awareness results from smearing artifacts.