Dissociating cognitive and motoric precursors of human self-initiated action

Abstract

Across-trial variability of EEG decreases more markedly prior to self-initiated than prior to externally-triggered actions, providing a novel neural precursor for volitional action. However, it remains unclear whether this neural convergence is an early, deliberative stage, or a late, execution-related stage in the chain of cognitive processes that transform intentions to actions. We report two experiments addressing these questions. Self-initiated actions were operationalized as endogenous skip responses while waiting for target stimuli in a perceptual decision task. These self-initiated skips were compared to blocks where participants were instructed to skip. EEG variability decreased more markedly prior to self-initiated compared to externally-triggered skip actions, replicating previous findings.\n\nImportantly, this EEG convergence was stronger at fronto-midline electrodes than at either the electrode contralateral or ipsilateral to the hand assigned to the skip action in each block (Experiment 1). Further, convergence was stronger when availability of skip responses was rationed, encouraging deliberate planning before skipping (Experiment 2). This suggests that the initiation of voluntary actions involves a bilaterally-distributed, effector-independent process related to deliberation. A consistent process of volition is detectable during early, deliberative planning, and not only during late, execution-related time windows.