If you've ever wondered why you remember surprises so vividly, new research has uncovered a fundamental pathway that encodes novel information in the brain differently.
Researchers from The University of Sydney (USyd) investigated what's going on in our heads when we encounter a surprise event, compared with our expectations. They found that the brain switches up its energy allocations to take in more data from our environment when the unpredictable occurs.
“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 Dr Reuben Rideaux from the School of Psychology at USyd.
“Our brain is constantly under pressure to make decisions, receiving a huge amount of sensory information from our environment," he adds. "So, it needs to save energy where it can."
Think of it like the brain being in low-power mode when it's taking in familiar sensory information, as if we had an autopilot switch – even if it might not feel like it to us.
When the brain processes the predictable, scientists found that it begins to respond based on previous knowledge, before we even experience the event. This results in a quicker response, even if our brain doesn't take in all of the details. It's essentially "been there, done that".
“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,’" Rideaux explains.
“But during unexpected events it’s like a software update or patch," he adds. "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."
The researchers discovered this after studying 40 participants presented with simple visual flashes around a circle. Volunteers also had their brain waves measured via EEG and had their pupil responses tracked.
In the experiment, participants' reaction times and accuracy were measured as they responded to the flashes in front of them. At random moments, the team changed the pattern of the flashes. The sequence went from predictable to unexpected.
They found that participants had a distinctly different neurological response to the expected events versus the surprise flash patterns. Individuals responded faster to the expected events but couldn't remember the precise locations of specific flashes when asked for details.
Both expected and surprise events were tracked in the cortex within 100 milliseconds of a flash. However, the unpredictable events were clearer in the brain wave recordings.
“The debate had been focused on whether the brain prioritised expected or unexpected information,” says lead author, PhD candidate Ziyue Hu, from the School of Psychology at USyd. “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 team also uncovered a surprise of its own: Our brains react to predictable events in two distinct stages. The first stage occurs when the brain reacts to what is about to happen and prepares accordingly – allowing the body to react faster.
Then, in the second stage, once the predictable event has played out as expected, the brain switches to that low-power mode to save energy, and it skips processing information from the environment thoroughly because it already has that data on file.
The researchers use the example of elite athletes – in this case, a female tennis pro – to illustrate the process.
“Imagine a professional tennis player who knows where her opponent’s next serve is going to land," Rideaux offers. "Their experience makes them move toward 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.
“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," he adds. “But it’s the rare surprise serve down the middle, which she'll remember with vivid spatial precision.”
Rideaux and his colleagues now hope to explore how these mechanisms develop over time and experience, and what environmental cues influence the processes.
They're also eager to investigate how this brain response could be used in the emerging field of blending neural networks and artificial intelligence to maximize function and energy efficiency.
The study was published in The Journal of Neuroscience.
Source: The University of Sydney via Scimex
Fact-checked by Mike McRae
