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Australian researchers have uncovered what happens behind the scenes in our brain when we’re faced with a predictable situation versus a surprise, giving vital clues in a long-standing mystery in neuroscience.

The researchers found that during surprising events, our brain is wired to direct energy to take in more sensory information from our environment.

This is why we remember unexpected events more vividly and accurately. Our brain then updates its own internal memory.

In comparison, when something is familiar or expected, the brain begins to respond to it before it even happens, which is what saves precious milliseconds. When something predictable appears, the brain makes us respond faster but doesn’t bother encoding it in full detail.

“Our study is a fascinating insight into how the brain uses predictions to help us better perceive and interact with the world,” says senior author from the School of Psychology at the ������.

“Our brain is constantly under pressure to make decisions, receiving a huge amount of sensory information from our environment. So, it needs to save energy where it can.

“When the brain is faced with a predictable situation, it goes ‘I already know what this is, I don’t need to spend energy processing it carefully.’

“But during unexpected events it’s like a software update or patch. Our brain wants to update our internal memory of the world to make sure we’re prepared for the future, so the energy is dedicated to collect as much information as possible from our environment,” says Dr Rideaux.

The findings, published in , resolves a long-standing debate in neuroscience about ‘adaptive efficiency’, how our brain allocates neural energy to meet the pressures of environmental demands.

“The debate had been focused on whether the brain prioritised expected or unexpected information,” said lead author PhD candidate Ziyue Hu, from the School of Psychology.  

“We’ve found the answer is both. The brain has its cake and eats it too.”

“It’s incredible because this process all happens in milliseconds. This advances our understanding of how the brain balances speed and accuracy and how prediction and attention shape how we perceive the world.”

The best real-world example that demonstrates this is professional sport. For high performance athletes, their experience enables them to predict and respond more quickly.

“Imagine a professional tennis player who knows where her opponent’s next serve is going to land. Their experience makes them move towards that spot before the ball is even struck and to get her racket in position to hit it back cleanly. Her brain had already prepared a motor response for the likely location and didn't bother encoding the precise location of the ball that confirmed what it already predicted,” says Dr Rideaux.

“That prediction buys her precious milliseconds, but if you ask her to recall frame by frame, exactly where the ball bounced inside the service box, her memory will be fuzzy.

“But it’s the rare surprise serve down the middle, which she'll remember with vivid spatial precision.”

To study this phenomenon, 40 participants viewed simple visual flashes appearing around a circle while researchers measured their brain activity using EEG (recording brain waves) and tracked their pupil responses.

The research team recorded the participant’s reaction times and accuracy. But crucially, at times the researchers would manipulate and deliberately change the pattern of the flashes.

Participants responded more quickly and accurately to expected events, but when asked to recall the exact location, their memory was worse than after the unexpected flashes.

One surprising finding was our brain reacts to familiar events in two stages.  

The first is when the brain first predicts what is about to happen and so prepares and primes our body to react quickly.

The second is when the brain recognises that the event is what it expected, and it saves energy by not processing this information from the environment as deeply.

Both expected and unexpected events were represented in the cortex within 100 milliseconds of participants seeing the flash, but the unexpected events were represented more clearly in the brain waves than the expected ones.

For the next stage of the research, Dr Rideaux’s team is interested in understanding how these mechanisms develop over time, and what ecological factors influence those pathways.

The team is also interested in exploring how these mechanisms can be applied in artificial brains (neural networks and artificial intelligence) to improve their efficiency or performance. 

Declaration: The authors declare no competing interests. This research was supported by a National Health and Medical Research Council and Investigator Grant.