What Is the Readiness Potential?

Abstract

The readiness potential (RP), a slow buildup of electrical potential recorded at the scalp using electroencephalography, has been associated with neural activity involved in movement preparation. It became famous thanks to Benjamin Libet (Brain 1983;106:623-642), who used the time difference between the RP and self-reported time of conscious intention to move to argue that we lack free will. The RP's informativeness about self-generated action and derivatively about free will has prompted continued research on this neural phenomenon. Here, we argue that recent advances in our understanding of the RP, including computational modeling of the phenomenon, call for a reassessment of its relevance for understanding volition and the philosophical problem of free will.

Keywords: computational model; consciousness; decision; free will; intention; volition.

Figure 1.

Key Figure Early- versus Late-Decision Accounts of the Readiness Potential (RP)/the Stochastic Accumulator Model (A) Early-decision accounts of the RP propose that the onset of the RP marks an inflection point in neural activity, the start of a process of planning and preparation for movement that culminates in a movement at t0. According to early-decision accounts, the neural decision to initiate movement is marked by the onset of the RP. (B) In late-decision accounts, the RP reflects the average time course of ongoing spontaneous fluctuations in neural firing rate, recruitment, or excitability when data are time-locked to crests in those fluctuations. The accumulation-to-bound model (AtBM; C–F) offers a late-decision account of the RP. The AtBM accounts for the RP using a leaky stochastic accumulator. The distribution of first crossing times (blue arrows in C) can be used to account for the distribution of waiting times in Libet’s [2] task (E). When the decision variable is time-locked to the threshold crossing (D), its average trajectory (sign reversed) as it approaches the threshold can be fit to the shape of the RP (F).