Do you have free choice? It may seem like a stupid question with an obvious answer, but it has troubled the minds of philosophers from Aristotle to Kant for thousands of years. Now, for the first time, scientists have recorded the changes that occur in the brain signals of monkeys when they make the free choice to change their minds.
The researchers, based at Stanford, used trained monkeys to perform decision-making tasks whilst tracking their brain activity as they completed them. With split-second accuracy, they were able to see when the monkey's brain made decisive decisions, hesitated, or changed its mind. This deeper understanding of decision-making will hopefully allow the lab to fine-tune their ongoing work on movement control and neural prostheses for people with paralysis.
“We are seeing many cognitive phenomena in the brain for the first time,” explained Matthew Kaufman, one of the authors now at Cold Spring Harbor Laboratory. “The most critical result of our work here is that we can track a single decision and see how the monkey arrived there: whether he decided quickly, slowly, or changed his mind halfway through.”
Kaufman trained two rhesus macaques (Macaca mulatta) to trace their finger through a simple maze to one of two targets. Sometimes, the choice of target was forced by blocking the other option, sometimes it was a genuinely free choice of which target to choose. The researchers could then switch this whilst the monkey was still making a decision, encouraging—but not forcing—them to change their mind.
During all this, the scientists used electrodes to monitor the activity of two brain regions involved in the planning of movement. The signals picked up from the electrodes were so precise that they allowed the researchers to reliably predict which of the targets the monkeys were favoring hundreds of milliseconds before they were told to move their finger.
Interestingly, the researchers were required to carry out all experiments on each monkey within in a single day, as the neurons recorded were likely to change from day to day and so the results would not be comparable.
“We can now track single decisions with unprecedented precision,” says Kaufman. “We saw that the brain activity for a typical free choice looked just like it did for a forced choice. But a few of the free choices were different. Occasionally, [the monkey] was indecisive for a moment before he made any plan at all. About one time in eight, he made a plan quickly but spontaneously changed his mind a moment later.”
While hesitating, indecision, and wavering might feel instinctive to us, this research, published in the journal eLife, is the first to observe how changes occur on a neural level. The results may help further the development of prosthetic arms that are controlled by the patient's brain.