Do Rats Have Free Will?

New research on the neural basis of 'spontaneous' actions in rats could shed light on the philosophical mystery that is human 'free will'. The study, just published in Nature Neuroscience, is called Neural antecedents of self-initiated actions in secondary motor cortex. It's from researchers Masayoshi Murakami and colleagues of Portugal's excellently-named Champalimaud Centre for the Unknown. The senior author is Zach Mainen, whom I interviewed recently after he helped organize the campaign for reform of Europe's Human Brain Project. Murakami et al. trained rats to perform a task requiring patience. In each trial, the rat heard a sound and had to wait in place until a second sound occured. If they waited, they got a large amount of water as a reward. If they moved to get some water too soon, however, they only got a small amount. Using tiny electrodes implanted in the premotor cortex of the rats' brains, Murakami et al. discovered that some neurons seemed to act as "integrators" (or counters) - over the course of the waiting period, their firing activity gradually increased. If activity reached a certain threshold before the second sound played, the rat would stop waiting and 'spontaneously' decide to go for the small reward. These "integrator" neurons didn't always count at the same speed, however. On some trials, they 'ramped up' more quickly - and when this happened, the rat was more impatient. This image shows the relationship between ramp up rates and waiting time -