Fifty Years Without Free Will Aaron Schurger (Cognitive Neuroimaging Unit, INSERM, NeuroSpin, Lausanne, Switzerland) PL5
How are actions initiated by the human brain when there is no external sensory cue or other immediate imperative? How do subtle ongoing interactions within the brain and between the brain, body, and sensory context influence the spontaneous initiation of action? How should we approach the problem of trying to identify the neural events that cause spontaneous voluntary action? Much is understood about how the brain decides between competing alternatives, leading to different behavioral responses. But far less is known about how the brain decides "when" to perform an action, or "whether" to perform an action in the first place, especially in a context where there is no sensory cue to act such as during foraging. Fifty years ago, in 1965, scientists discovered a slow buildup of neural activity that precedes the onset of spontaneous self-initiated movements (movements made without any cue telling you when to move). This buildup was dubbed the "readiness potential" or bereitschaftspotential, and has since been confirmed at the single-neuron level. For the past five decades it has been assumed to reflect a process of "planning and preparation for movement". In the 1980s the readiness potential was used to argue that we do not have conscious free will, because the readiness potential appears to begin even before we are aware of our own conscious decision to act. Now we and others have challenged that long-standing interpretation by showing that the early part of the readiness potential might reflect sub-threshold random fluctuations in brain activity that have an influence on the precise moment that the movement begins. These fluctuations thus appear as part of the "signal" when we analyze the data time-locked to the time of movement onset. This fundamental insight leads to novel and testable predictions concerning both objective (brain signals and behavior) and subjective (the perceived time of the conscious intention) phenomena, and may also have important, philosophical implications.