Abstract
Inhibition of prepotent action is an important aspect of self-control, particularly in social contexts. Action inhibition and its neural bases have been extensively studied. However, the neural precursors of free decisions to inhibit have hardly been studied. We asked participants to freely choose to either make a rapid key press in response to a visual cue, or to transiently inhibit action, and briefly delay responding. The task required a behavioural response on each trial, so trials involving inhibition could be distinguished from those without inhibition as those showing slower reaction times. We used this criterion to classify free-choice trials as either rapid or inhibited/delayed. For 13 participants, we measured the mean amplitude of the ERP activity at electrode Cz in three subsequent 50 ms time windows prior to the onset of the signal that either instructed to respond or inhibit, or gave participants a free choice. In two of these 50 ms time windows (−150 to −100, and −100 to −50 ms relative to action onset), the amplitude of prestimulus ERP differed between trials where participants ”freely” chose whether to inhibit or to respond rapidly. Larger prestimulus ERP amplitudes were associated with trials in which participants decided to act rapidly as compared to trials in which they decided to delay their responses. Last-moment decisions to inhibit or delay may depend on unconscious preparatory neural activity.
Highlights
Decisions for action can be decomposed into at least three separate functional components [1], associated with the selection of what action to make; when to make it and whether to make it at all
The main effect of source of decision (F1,13 = 7.15; p = 0.019) arose because free-choice responses were slower than instructed responses. This suggests that the free decision to respond rapidly or to transiently inhibit and delay involved a time-consuming cognitive process occurring after the instruction signal
Participants were told that they could blink only after having made an action, to prevent the wellknown tendency to blink and press the key at the same time. This instruction could explain the observed differences in the proportion of rejected trials between action and transient inhibition conditions Earlier key presses in the rapid conditions might have been the cause of more blinks occurring during the epoch of interest
Summary
Decisions for action can be decomposed into at least three separate functional components [1], associated with the selection of what action to make (what component); when to make it (when component) and whether to make it at all. The whether component is related to last-minute inhibition of an action that has been prepared and is ready for execution This component may be important as a mechanism for self-control [2]. Previous studies have linked preparatory activity preceding voluntary action to decisions about what action to make e.g., [3,4,5], or when to make it [6,7]. Both these components of voluntary decision were shown to have unconscious neural precursors. Neural precursors of voluntary inhibition have not yet been identified experimentally
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