The question of whether humans have free will has been discussed for centuries by philosophers and religious scholars, and more recently by neuroscientists. Haynes and colleagues have now added fuel to the debate by showing that activity in two non-motor-related cortical areas can predict the outcome of a movement decision up to 10 seconds before an individual becomes aware of the decision.
Volunteers were placed in a functional MRI scanner and were asked to press a button with either their left or their right index finger whenever they wanted to. Throughout the experiment the volunteers watched a screen that showed a succession of letters, and they had to remember the letter that was presented on the screen at the moment they made the decision which button to press. This revealed that most of the decisions were consciously formed 1 second before the motor response was executed.
The authors then analyzed the activity in different brain areas during the time preceding the button press, using pattern-based decoders. This type of analysis can detect 'signature' patterns of activity that are associated with a particular decision. The authors found such patterns of activity in Brodmann area 10 and in the parietal cortex (the precuneus/posterior cingulate cortex) — areas that are thought to be involved in executive function and self-processing — and the patterns predicted with high accuracy which button would be pressed. Intriguingly, the signatures appeared up to 7 seconds before the volunteers consciously chose their motor response. Because the haemodynamic blood-oxygen-level-dependent response is thought to represent neuronal activity that occurred about 3 seconds earlier, this finding suggests that activity in the two areas encodes decisions approximately 10 seconds before they enter consciousness.
Activity patterns that were observed in the supplemental and presupplemental motor area approximately 5 seconds prior to a decision entering awareness predicted its timing, indicating that different brain areas might be involved in forming the intention to make a movement and deciding when to make it.
Although it is hard to imagine that our decisions might be made subconsciously, these findings have important implications. Can people be held accountable for their actions if they do not become aware of their decisions until after they are made? You decide.