Rat study sheds light on question of human ‘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.

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.

Why did the integrators sometimes count faster than other times? Murakami et al. found a second class of neurons, whose rate of firing (which varied seemingly at random) predicted the rate at which the integrators “counted up”. The authors suggest, therefore, that these latter neurons provide inputs to the neural integrators. When the total amount of input reaches a threshold, a ‘spontaneous’ action is triggered.

What does this have to do with free will? Well, it all goes back to 1983, when a neuroscientist called Benjamin Libet found, using EEG, that a certain pattern of brain activity – a “readiness potential” – occurs in the human brain just before ‘spontaneous’ actions. In fact, this brain event happens even before we are aware of deciding to act.

Libet’s much-discussed finding has been seen as evidence against free will because it seems to suggest that ‘the brain decides to act before we do’.

Read full, original article: Do Rats Have Free Will?

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