Neural Activity in Brain Motor Does Your Brain Know you Want to Move Before you Know it Yourself?

A groundbreaking study using a brain-machine interface shows how the brain perceives the timing of intentions and actions—offering rare insight into the neural roots of free will.

Researchers led by Jean-Paul Noel at the University of Minnesota, United States, have decoupled intentions, actions and their effects by manipulating the brain-machine interface that allows a person with otherwise paralyzed arms and legs to squeeze a ball when they want to. Published in the open-access journal Plos Biology on April 17th, the study reveals temporal binding between intentions and actions, which makes actions seem to happen faster when they are intentional.

Separating intentions from actions was made possible because of a brain-machine interface. The participant was paralyzed with damage to their C4/C5 vertebrae and had 96 electrodes implanted in the hand region of their motor cortex. As they tried to squeeze a ball, a machine-learning algorithm looked at all the signals coming to the electrodes, and learned which activity pattern meant “squeeze” (close) and which meant “relax” (open). Once learned, the machine could send an electrical signal to the appropriate hand muscles, allowing the participant to squeeze the ball, which then delivered a sound. On average, the participant perceived the time from intention to action to be 71 ms, which was slightly faster than the real time duration.

The heart of the study involved systematically removing each part of the chain of events. By randomly stimulating the participant’s hand to squeeze the ball, the researchers were able to eliminate intentions. In this case, actions were judged to occur much later. On the other hand, when the participant tried to squeeze the ball, but actions were prevented by not stimulating the hand, intentions were perceived to happen much earlier if the sound was still played after the machine decoded the intention. Perceived timing did not change if the sound was not played. These results indicated a compressed temporal binding between intention and action. Recordings from the electrodes, which normally cannot be done in humans, showed that the motor cortex encodes these intentions.

The authors add, “The work builds on a long tradition trying to establish the temporal relationship between moving, the onset of the subjective experience of intending the movement, and the neural correlates of this intention. While there have been quite a number of non-invasive studies on this topic, only a single study prior to our was able to measure single neurons - the gold-standard in neuroscience - in humans while asking them to report when they first ‘felt the urge to move’.”

The authors continue, “This prior work (Fried et al., 2011) showed that certain brain areas (all in the frontal cortex) know about the intention to move up to a second prior to when we experience that intention. You can imagine this created quite the debate regarding whether humans have free will or not. Our study contributes to this debate by recording single neurons in the primary motor cortex. We show that firing of neurons in this area (the last cortical node before the spinal cord, which ultimately elicits movements) co-occur with the subjective experience of intending a movement.”

The authors conclude, “The work would have not been possible without expertise from a number of contributors, including neurosurgeons, neuroengineers and neuroscientists, among others.”

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