Our brain performs complex math to make sense of world

We may find it difficult to calculate complicated probabilities, but the brain constantly carries out complex mathematical computations without our awareness to make sense of the world, scientists say.

Researchers at Princeton University in the US showed that our brains combine complicated observations from our surroundings into a simple assessment of the situation that aids our behaviour and decisions.

They found that our brains can accurately track the likelihood of several explanations for what we see around us.

They traced these abilities to a region of the brain located just behind our eyes known as the orbitofrontal cortex.

"When I try to cross the street, I'm not actually analysing every bit of the scene," said Yael Niv, an associate professor at the Princeton Neuroscience Institute (PNI).

"I'm constructing a narrative that I base my decision on, such as, 'That car is slowing down because of the red light'," he said.

Stephanie Chan, who earned her doctorate from Princeton , hypothesised that the brain keeps track of these possibilities in a way that is simpler than a comprehensive description of the situation, but more complex than a single explanation.

She studied the idea that the brain calculates a distribution of probabilities for many distinct possibilities.

To find out where and how the brain tracks these probabilities, the team needed to coax study participants to compare probabilities without thinking about actual numbers.

If participants tried explicitly to do the math, they would fail, said Kenneth Norman, professor at PNI.

"Our brains are horrible at arithmetic. Our implicit computations are so much better than our explicit computations," Norman said.

To study these implicit computations, the team tracked the brain activity of participants as they explored a virtual "safari park" split into four zones - blue, green, pink and yellow. Each zone contained a different assortment of elephants, giraffes, hippos, lions and zebras.

The task forced the brain to use previous observations of these animals to decide in which coloured zones various arrangements of the animals were likely to be found.

To find out where the brain performs this feat, the researchers had participants perform the task while undergoing functional magnetic resonance imaging (fMRI), which unveils the regions of the brain that are most active at a given time.

The researchers expected the brain to track the situation as a series of four probabilities so they looked for brain regions in which the pattern of activity changed together with the four probabilities.

The best match for this search was the orbitofrontal cortex, a brain region implicated in carrying out complex plans, learning how a setting or situation has changed since last seen, and high-order thinking.

The research was published in the Journal of Neuroscience.