How do memories survive sleep? It’s all about intention
10-11-2025

How do memories survive sleep? It’s all about intention

A simple instruction can shape what sticks in your head. In a new study, scientists instructed people to remember or forget words and then checked what words they retained in their memory after a 12-hour delay.

Some volunteers stayed awake between sessions, while others slept wearing an EEG headband. This device measures electrical activity in the brain through sensors on the scalp.

The primary result was clear: instructions mattered more than emotion or sleep.

Memory put to the test

The team used a classic “directed forgetting” task – a memory test in which participants are instructed to deliberately remember or forget specific information. This approach helps researchers separate deliberate control from automatic, gut-level reactions.

The words were selected from the Affective Norms for English Words (ANEW) manual, a well-known research dataset of rated words. Half of the words had negative meanings.

The participants viewed 100 words, each followed by an R-cue to remember or an F-cue to forget.

The volunteers completed an immediate recognition test and then returned 12 hours later for free recall. Forty-five people completed the task online, while 53 completed their tasks under lab observation.

In the lab group, the sleep subset wore EEG headbands at home. That allowed the team to relate memory to specific sleep features without changing bedtime routines.

Remembering was the clear winner

What the researchers uncovered was interesting to say the least: instruction won. Participants recalled more of the words they had been asked to remember than the words they were instructed to forget.

Emotion did not override that control. Negative words helped only when they lined up with a remember-cue, boosting recognition more than recall.

“What we intend to remember and to forget can be powerful,” said study lead author Dr. Laura Kurdziel from Merrimack College (MC). 

The experiment also revealed false memories. Participants tended to mistake negative foils for familiar items, showing how emotion can distort memory – even for information that was never actually learned.

Sleeping versus staying awake

Across the full sample, sleeping versus staying awake did not change how many target words people recalled. While that finding may surprise many, it fits a growing view that how we sleep matters more than the sleep label itself.

Sleep patterns told a more detailed story. A higher number of sleep spindles – brief bursts of brain activity during light sleep – were linked to stronger memory processing and better recall of negative items that had been cued for remembering.

This finding points to selective stabilization of memories during light non-REM sleep.

Slow-wave sleep (SWS), the deepest stage of non-REM sleep, was associated with lower overall recall. The more time participants spent in this stage, the fewer items they remembered.

The pattern hints that deep sleep may sometimes clear rather than be kept; a possibility the authors note requires caution, given the modest EEG sample.

Instructions are key to memory

When you set a goal to retain a piece of information, your attention system marks it. Those marks can bias the hippocampus: the brain region that organizes new memories and links them to existing ones.

Once that occurs, the hippocampus recognizes that item as relevant and helps route it toward longer-term storage in the neocortex, the outer layer of the brain involved in conscious thought and memory retrieval.

That top-down tag also suppresses clutter. By dampening competing traces, the target faces less interference during later retrieval.

Emotion still matters, just not as the main driver in this task. It acts like a volume knob that raises the strength of signals already labeled as worth keeping.

Sleep helps us remember, and forget

Earlier sleep studies showed that spindles track successful intentional remembering in directed forgetting designs. That link appears in prior research and is echoed here at night.

REM-related theta rhythms have been tied to the consolidation of emotional memories.

The association shows up in earlier work, testing the role of REM sleep in storing emotional experiences, and can help explain why theta tracked false alarms to negative foils.

Some scientists argue that sleep can also promote forgetting when that serves a healthy memory system. One such review outlines why clearing low-priority traces can be adaptive.

Intention is not a small thing. Setting a clear goal to remember can give your brain a target to prioritize.

Sleep still matters for health, but its role in memory looks selective. The architecture of sleep may favor what you marked as important over what simply felt intense.

The study is published in the journal Frontiers in Behavioral Neuroscience.

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