The brain pauses before acting, even without key region

The medial prefrontal cortex (mPFC) is a brain region just behind the forehead. It has long been associated with complex decision-making, impulse control, and adapting behaviour in dangerous situations. Many researchers assume it actively directs the choice between acting and holding back.

A new study in eLife questions that assumption. The researchers used mice trained to avoid dangerous situations. They measured brain activity while the animals made decisions, and temporarily switched off the mPFC using optogenetics (a technique that turns neurons on and off with light).

Activity is not the same as control

The mPFC was active during task moments. But much of that activity overlapped with activity in the visual cortex, a region not considered a decision-making centre. The apparently task-relevant signals were partly a reflection of movement and signal detection, not genuine decision-making control.

More strikingly, when the researchers switched off the mPFC, the avoidance behaviour of the mice barely changed. The brain could perform the tasks without this region. Only in the most complex task variants, where mice had to choose between acting and withholding, did specific neurons encode the choice. But even then, switching off the mPFC had little effect on performance.

Relevance for ageing and dementia

The finding that neural encoding and causal control can be dissociated is methodologically relevant across neuroscience. From a longevity perspective, it is noteworthy that the prefrontal cortex is among the first regions to be affected by ageing and dementia. If this area plays mainly a registering rather than a controlling role in much behaviour, that has implications for how we should interpret age-related behavioural changes.

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