Image Credit: Scientific Frontline
Scientific Frontline: "At a Glance" Summary: Neural Reactivation of Lost Memories
- Main Discovery: Seemingly forgotten memories persist in the human brain and can be neurally reactivated even when they fail to reach conscious awareness.
- Methodology: Researchers utilized Magnetoencephalography alongside a machine learning algorithm to track unique neural signatures while participants completed a paired associates task, attempting to recall specific videos linked to target words.
- Key Data: Successful conscious memory recall correlates with rhythmic fluctuations in the alpha band of the reactivated memory signal, accompanied by a simultaneous decrease in total sensory neocortical alpha power.
- Significance: Conscious retrieval requires a memory signal to pulse rhythmically to overcome background neural noise, indicating that recall failure is often an issue of signal detection rather than complete memory erasure.
- Future Application: Therapeutic approaches for cognitive decline and conditions like dementia could be re-engineered to help existing, dormant memories break through into conscious awareness rather than focusing solely on rebuilding lost information.
- Branch of Science: Neuroscience and Cognitive Psychology.
Researchers have used brain imaging to show how memories can be reactivated in the brain without them reaching conscious awareness, showing that these memories persist even when we think they have been forgotten.
Scientists from the University of Nottingham’s School of Psychology used Magnetoencephalography (MEG) to show how our brains reactivate memories even when we can’t recall them, suggesting that the brain remembers even if we don’t. The results have been published in Journal of Neuroscience.
Neural oscillations are rhythmic electrical activity in the brain often referred to as brain waves. These are essential for encoding, storing, and retrieving memories by synchronizing neural populations. Oscillations specifically facilitate memory formation, spatial navigation, and episodic memory binding in the hippocampus, while alpha and beta bands are often linked to cortical processing during long-term memory tasks.
In the study, participants completed a paired associates task. They were asked to vividly associate a video with a word and later shown each word and recall the associated video. MEG captured their brain activity throughout, and a machine learning algorithm (trained to recognize the brain’s unique signature for each video) was used to detect whether the brain could reactivate a specific memory, even if the participant failed to overtly recall it.
The results showed that while the brain reactivated memories regardless of whether they were consciously recalled, the reactivated memory signal fluctuated more rhythmically in the alpha band when the memory was successfully recalled, as though this rhythmic pattern helped the memory signal to be heard over all the background neural noise that otherwise might mask it.
Dr. Benjamin Griffiths from the School of Psychology led this study and explains: “What we showed is that even when the brain can reactivate the right memory, it doesn't guarantee you'll become aware of it. Instead, what seems to matter is that the memory rhythmically pulses so that it can be detected above and beyond other neural activity. If you think about a football ground, if everyone is chatting you can’t hear what is being said but if everyone starts singing the same song you can hear it clearly, we speculate that a similar idea is involved in the brain’s recall of memories.”
The researchers also found a decrease in total sensory neocortical alpha power accompanies this memory rhythm, Ben explains: “This finding can be likened to the general background noise in the stadium dropping. When the overall chatter dies down, even a modest chant from the fans becomes easier to hear.”
These findings may have real implications for conditions like dementia. Current treatments often assume that when someone can't remember, the memory itself is gone. But if memories are being reactivated in the brain and simply failing to reach consciousness, it suggests we might need a different approach — one focused not on rebuilding lost memories, but on helping existing ones break through into awareness.
Published in journal: Journal of Neuroscience
Title: Alpha oscillations track the projection of reactivated memories into conscious awareness
Authors: Benjamin J. Griffiths
Source/Credit: University of Nottingham
Reference Number: ns030526_01
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