What happens in our brains when we recall a memory? It’s more complex than you think

Our brains are incredible machines that can send us down everwinding paths of history, flitting from painful memories to ones that fill us with joy in an instant, or even teleporting us into our imagined future.

What happens in our brains when we recall a memory? It’s more complex than you think

And while daydreaming may seem effortless, the act of moving forward and backward in time within our own thoughts is far from simple. New research has discovered that when we recall a memory, or look to the future, our brain is actually working hard using a mix of different systems.

The study, published in the journal Nature Human Behaviour, was led by Dr. Vadim Axelrod and Professor Moshe Bar from Bar-Ilan University. The team asked volunteers to imagine a scene and studied the active brain regions to identify the complex network of systems that work together when we have internal thoughts, as well as when we empathise with others.

A total of 41 healthy participants were scanned using MRI. While lying in the scanner, the participants were asked to generate “mental experiences” associated with a given picture.

 Each had to imagine what happened before (‘past imagery’) or after (‘future imagery’) the scene, they each had to recall a personal episodic memory related to the scene (‘episodic memory’), and they had to imagine themselves as the person in the picture (‘empathising’).

From these results, Axelrod and his team were able to pinpoint three distinct cognitive systems activated in the brain during thinking.

The researchers noticed that brain activity when recalling an episodic memory caused a “clear, positive, inverted U-shape” to appear on the scan in the posterior cingulate cortex (PCC) and angular gyrus, as well as in the medial prefrontal cortex (mPFC). At the same time, there was a negative U-shape created in the parahippocampal cortex (PHC).


Additionally, in the PCC and mPFC regions, the team noticed visibly higher responses in the episodic memory condition compared with the other conditions. A plausible explanation, the team explains, is that recalling personal events creates stronger self-related processing compared to imagining what happened before and after, or empathising with a stranger. In effect, it illicits a heightened emotional response.

But while all three systems were active at the time of recalling a memory, what was most puzzling, as Axelrod explains, was how sensory input is not needed. All we need to do is close our eyes and we can be transported forward or backward in time without being prompted by a smell, photo or similar.

“We might have infinitely many internal experiences,” Axelrod tells me. “It should be emphasised that it is not just about our memories, it might be also future imagery of the future or just [the] mind wandering.”

So while we might imagine our thoughts to come all at once and in one single entity, the brain actually processes it using different systems.

“This might sound counterintuitive because each of our experiences is felt as a monolithic whole,” Axlerod continued. “When you imagine your next vacation, you do not feel that there is part of your brain that builds a virtual scene and another part of your brain that time-travels.”

The team hope that its study will pave the way to further studies that are able to spot other cognitive systems that go beyond the three identified.

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