Researchers at the University of Nottingham have demonstrated that memories can be reactivated in the brain without reaching conscious awareness. Using Magnetoencephalography (MEG), scientists from the School of Psychology observed that neural activity associated with specific memories could occur even when participants could not consciously recall them. The findings were published in the Journal of Neuroscience.
Participants in the study performed a paired associates task, where they linked a video to a word and later attempted to recall the video upon seeing each word. MEG was used to record their brain activity during these tasks. A machine learning algorithm, trained to identify unique neural signatures for each video, detected memory reactivation even when participants failed to remember consciously.
The study found that memory signals fluctuated more rhythmically in the alpha band when participants successfully recalled information. According to Dr. Benjamin Griffiths, who led the research, "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 noted a decrease in total sensory neocortical alpha power during this process. Dr. Griffiths explained: "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 results may affect approaches for treating conditions such as dementia by suggesting that some forgotten memories might still exist within neural circuits but fail to reach conscious awareness. As Dr. Griffiths stated: "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."
