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Neural Antecedents of Spontaneous Voluntary Movement: A New Perspective

The neuroscience of volition is an emerging subfield of the brain sciences, with hundreds of papers on the role of consciousness in action formation published each year. This makes the state-of-the-art in the discipline poorly accessible to newcomers and difficult to follow even for experts in the field. Here we provide a comprehensive summary of research in this field since its inception that will be useful to both groups. We also discuss important ideas that have received little coverage in the literature so far. We systematically reviewed a set of 2220 publications, with detailed consideration of almost 500 of the most relevant papers. We provide a thorough introduction to the seminal work of Benjamin Libet from the 1960s to 1980s. We also discuss common criticisms of Libet’s method, including temporal introspection, the interpretation of the assumed physiological correlates of volition, and various conceptual issues. We conclude with recent advances and potential future directions in the field, highlighting modern methodological approaches to volition, as well as important recent findings.

Free will has been at the heart of philosophical and scientific discussions for many years. However, recent advances in neuroscience have been perceived as a threat to the commonsense notion of free will as they challenge two core requirements for actions to be free. The first is the notion of determinism and free will, i.e., decisions and actions must not be entirely determined by antecedent causes. The second is the notion of mental causation, i.e., our mental state must have causal effects in the physical world, in other words, actions are caused by conscious intention.

We present the classical philosophical positions related to determinism and mental causation, and discuss how neuroscience could shed a new light on the philosophical debate based on recent experimental findings. Overall, we conclude that the current evidence is insufficient to undermine free will.

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.

While the question whether free will exists or not has concerned philosophers for centuries, empirical research on this question is relatively young. About 35 years ago Benjamin Libet designed an experiment that challenged the common intuition of free will, namely that conscious intentions are causally efficacious. Libet demonstrated that conscious intentions are preceded by a specific pattern of brain activation, suggesting that unconscious processes determine our decisions and we are only retrospectively informed about these decisions. Libet-style experiments have ever since dominated the discourse about the existence of free will and have found their way into the public media. Here we review the most important challenges to the common interpretation of Libet-style tasks and argue that the common interpretation is questionable. Brain activity preceding conscious decisions reflects the decision process rather than its outcome. Furthermore, the decision process is configured by conditional intentions that participants form at the beginning of the experiment. We conclude that Libet-style tasks do not provide a serious challenge to our intuition of free will.

Sense of agency (SoA) is the feeling of being the author of given actions and their effects. Recent works have investigated the cue integration approach to agency, according to which different predictive and inferential cues form SoA. In the current research we focus on how two such cues, i.e. accuracy of sensorimotor prediction and prior causal belief, influence SoA measured by temporal binding (TB) and questionnaires. Our results show that whereas learnt action effects produce normal TB and explicit agency, unexpected oddball effects produce enhanced TB but diminished explicit agency. Increased binding was modulated by temporal prediction, but not by identity prediction. A few interpretations of the results are given, including cue integration and pre-activation mechanisms. The research casts new light on the mechanisms and dynamics of TB and adds to the evidence for discrepancies between SoA measures.