How the brain decides

2008-11-13 07:50

Paris - In making a decision, our brains operate like a bookie's computer, weighing the actions of others in the same way that we learn from our mistakes in order to calculate the odds, according to a study released on Wednesday.

Scientists observing the brain activity of volunteers who worked through a series of tests say the results challenge conventional theories about how - and where - decisions are formed in the brain.

The findings could also shed light on the mechanisms behind autism, a condition characterised by the inability to predict how others will behave, the authors said.

Two streams of data

Earlier research on the neural cogs of decision-making has found that the brain processes two separate streams of data.

One is based on our own experience and our record of success or failure in similar circumstances. The brain learns from its errors: if you were wrong, you have to learn something and work out what to do next time.

The other information stream flows from the fact that we are social animals, and that we are influenced by what others do and say.

"It is much more complicated to try to figure out how to learn from other people's behaviour," said Timothy Behrens, a researcher at the University of Oxford and the main architect of the study.

Most scientists had assumed that the neural underpinning of this second kind of learning was far more complicated than the first, which essentially is an system of reward and punishment.

Not so, Behrens told AFP in an interview.

"The brain is able to learn about this social value - how trustworthy someone is, or how much we should copy him - using the same kind of basic computational mechanism that we know they use when learning about rewards," he said by phone.

'Social processing'

The paper, published in the London-based journal Nature, may change the way scientists study how the brain integrates social inputs into the choices we make, he added.

"Up to now social processing has been a bit of a dark field because it has been very difficult to make formal models of how it works," he said.

In the experiments, subjects separately tracked the likelihood of a correct action and of receiving good advice, and then combined the two into a single probability of a correct response.

The outcome is also consistent with early research showing neurological anomalies in precisely the same part of the brain - called the superior temporal sulcus - affected in persons who are autistic.

The superior temporal sulcus is the last part of the brain to develop fully, which could help explain why teenagers may have trouble figuring out how their words and actions affect others, Behrens said.

The study also shows that another part of the brain involved in how we make choices - the anterior cingulate cortex - has a section that specialises in dealing with rewards information.

Just a centimetre away is another section that does the same thing, but processes social information.

Together, they go beyond simply noting that an outcome is different from what was expected, and "work out how valuable that information is and how much I should change my behaviour", Behrens said.

Seeing which of the two parts light up in brain imaging tests could show whether someone takes advice easily, or more likely to ignore such advice and "go with his own gut feeling", he added.

- AFP