Category: Memory

What predicts why you remember some information and forget the rest?

The brain has to be ready to remember information or it is likely to be forgotten.

The hippocampus — the part of the brain important for memory — has to be in ‘encoding mode’.

In encoding mode, neurons in the hippocampus are firing at an accelerated rate.

Unfortunately, neuroscientists do not yet know how to put the hippocampus into encoding mode.

Professor John Wixted, study co-author, said:

“‘Encoding mode’, is more than simply paying attention to the task at hand.

It is paying attention to encoding, which selectively ramps up activity in the part of the brain that is the most important for making new memories: the hippocampus.

Since we know, based on earlier research, that people can actively suppress memory formation, it might be possible for people to get their hippocampus ready to encode as well.

But how one might go about doing that, we just don’t know yet.”

The conclusions come from a study of 34 epilepsy patients.

They were shown a series of words while the neuronal activity in various critical parts of their brain was monitored.

The results showed that the neuronal firing rate observed in the hippocampus about one second before a word was seen boosted its later recall.

Professor Stephen Goldinger, study co-author, said:

“If a person’s hippocampal neurons were already firing above baseline when they saw or heard a word, their brain was more likely to successfully remember that word later.”

Neuronal activity in other areas of the brain did not predict recall.

Professor Goldinger said:

“We think new memories are created by sparse collections of active neurons, and these neurons get bundled together into a memory.

This work suggests that when a lot of neurons are already firing at high levels, the neuronal selection process during memory formation works better.”

Neuroscientists have also suggested the brain has a ‘retrieval mode’ for when we want to recall memories.

Another study on those with epilepsy has shown that, like the encoding of memories, the neurons start to activate a second or more before people are aware of retrieving a memory.

The study was published in the journal PNAS (Urgolites et al., 2020).

It is possible to make some memories stronger while leaving others to fade.

The strongest memories are created by very rewarding and demanding experiences, new research reveals.

However, we make these memories still stronger by replaying them repeatedly in our minds.

Each time a memory is recalled and re-lived, the neuronal activity that sustains it is strengthened.

This means that we actually edit our memories by what we choose to recall and replay.

Keep running over distressing incidents and these become stronger.

Remembering happier times, though, makes these memories stronger.

Most people (but not all) have a tendency to forget the negative and replay the positive.

This bias is sometimes called ‘the psychological immune system’.

Our minds ‘fight off’ negative memories automatically to leave us feeling happier — or at least, that is the theory.

Professor Fabian Kloosterman, study co-author, said:

“One of the ways in which our brains consolidate memories is by mentally reliving the experience.

In biological terms, this boils down to the reactivation or replay of the neuronal activity patterns associated with a certain experience.

This replay occurs in hippocampal-cortical brain networks during rest or sleep.”

For the study, rats were trained to remember where food was located in a maze.

Mr Frédéric Michon, the study’s first author, explained the results:

“Perhaps unsurprisingly, we found that rats remembered better the location where they found the large reward.

But we also observed that this reward-related effect on memory was strongest when the food pellets were located in places that required more complex memory formation.”

The scientists then disrupted the rats’ memories before they could be consolidated.

This is the human equivalent to winning the lottery, but never thinking about it again.

The effect was to impair the rats’ memory.

If they couldn’t replay the memory to themselves about where the food pellet was, they found it harder to remember.

Professor Kloosterman said:

“Our results demonstrate that replay contributes to the finely tuned selective consolidation of memories.

Such insights could open future opportunities for treatments that help to strengthen memories, and could also help us understand memory decline in diseases such as dementia.”

The study was published in the journal Current Biology (Michon et al., 2019).

Stress can temporarily damage these cognitive abilities.

Stress makes it harder for people to plan for the future, new research finds.

This is because being under stress robs people of their ability to use their memory effectively.

Memory is vital for planning, explained Professor Anthony Wagner, study co-author:

“We draw on memory not just to project ourselves backward into the past but to project ourselves forward, to plan.

Stress can rob you of the ability to draw on cognitive systems underlying memory and goal-directed behavior that enable you to solve problems more quickly, more efficiently and more effectively.”

For the study, people sat in front of a computer and learned a series of routes through a virtual town.

People were then asked to navigate around the town, but some people were told they would be given a random electric shock at some point.

The results showed that stress made it harder for people to use and act on their memories.

With the electric shock in the back of their minds, people tended to wander randomly around in habitual patterns.

Brain scans revealed that stress caused lower activation in the hippocampus, an area of the brain important for memory.

Stress also reduced activation in the area of the brain linked to planning, the frontal-parietal lobes.

Professor Wagner said:

“It’s a form of neurocognitive privilege that people who are not stressed can draw on their memory systems to behave more optimally.

And we may fail to actually appreciate that some individuals might not be behaving as effectively or efficiently because they are dealing with something, like a health or economic stressor, that reduces that privilege.”

Stress seems to take the memory replay system offline, said Dr Thackery Brown, the study’s first author:

“Its kind of like our brain is pushed into a more low-level thought-process state, and that corresponds with this reduced planning behavior.”

The researchers are now looking at this effect in older age-groups, said Dr Brown:

“It’s a powerful thing to think about how stressful events might affect planning in your grandparents.

It affects us in our youth and as we interact with and care for older members of our family, and then it becomes relevant to us in a different way when we are, ourselves, older adults.”

The study was published in the journal Current Biology (Brown et al., 2020).