Our brains – and the brains of other animals – actually run through superfast replays of past experiences as we make decisions, says a new study.
This process isn’t one we usually have conscious access to – but without it, we might not be able to learn from the past at all.
Memory seems pretty straightforward at first glance, doesn’t it? We experience, say, a song or a scene, and later we’re able to replay it within our mind – which has led smart people throughout history to speculate that the external world “writes” itself directly onto our brains… somehow. But as Freud and other 19th-century psychoanalysts began to study memory more carefully, it soon became clear that the truth was much weirder.
For example, none of us – apart from strange patients like Solomon Shereshevsky – can remember everything we’ve ever experienced, or recall any given detail of our life at will. Our memories of emotionally significant events tend to be sharpest, while other memories seem to vanish; meanwhile, false implanted memories can seem utterly real – sometimes more real than genuine ones.
In fact, we now know that memories aren’t static “things” at all – our brains create them anew each time we recall them, and they change more and more with each performance. And not only that – study after study has proven that much of what we remember is simply made up by our brains.
So do we actually remember anything at all – or do we only think we do?
Well, before you go looking for a red pill to swallow, let’s talk about what this all has to do with decision-making.
In all vertebrates, one cryptic brain structure lies at the center of memory storage and recall: the hippocampus. To this day, no scientist is sure what, exactly, the hippocampus does – but recent studies have provided some intriguing clues. For example, special hippocampal neurons called place cells get excited when we return to a place we recognize – and damage to specific parts of the hippocampus can impair the formation of new memories or the recall of old ones.
And now, the journal Science reports, a team led by Loren Frank and Shantanu Jadhavat at the University of California, San Francisco have discovered that disrupting certain hippocampal communication patterns can seriously alter rats’ ability to learn and make decisions.
The team used electrodes in the rats’ brains to detect a pattern of hippocampal activity called a sharp-wave ripple, which they knew would appear when the rats learned something new – for instance, the location of a sugary treat.
The researchers also knew that a similar ripple would appear when a rat had to make a decision – for instance, where to turn in a maze – based on that memory. In short, certain ripple patterns seemed to represent “performances” of certain memories in the rats’ brains.
So the researchers tried something: whenever they detected a recall ripple, they disrupted it with a small burst of electricity.1 And as the team suspected, this disruption made the rats behave as though they’d forgotten what they knew:
We interrupted awake SWRs in animals learning a spatial alternation task. We observed a specific learning and performance deficit that persisted throughout training.
But wait… it gets weirder. The rest of the rats’ brains still behaved as though the memory was intact – for example, their hippocampal place cells still responded to the familiar place:
SWR interruption left place field activity and post-experience SWR reactivation intact.
This must’ve left the rats with a surreal sense of deja vu – a feeling that they somehow knew which direction was the right one, even though they had no memory of why.
As it turns out, this experiment is filled with eerie echoes of how we humans make most of our decisions. Studies have shown that most of the information you use to make decisions isn’t accessible to your conscious mind at all – and that most of your decisions aren’t based on specific facts anyway, but on feelings; instincts that a certain choice is the “right” one for you.
Like memories, feelings aren’t created by your conscious awareness – they’re presented to your conscious awareness by ancient brain processes you’ll never see. The amount of data your conscious mind can hold at once is only a tiny droplet of a vast dark sea that froths and churns ceaselessly in the unlit corridors of your brain.
And all your conscious mind can do is shine the weakest of light-beams into those shadowy depths.
What do you think lurks down there?
1. Interestingly, researchers have also found that cannabis (marijuana) consumption disrupts hippocampal sharp-wave ripples.