Researchers have used advanced brain imaging to demonstrate that memories can be reactivated in the brain even when they do not reach conscious awareness, indicating that such memories may continue to exist even when they appear to be forgotten.
Scientists at the University of Nottingham’s School of Psychology conducted the study using Magnetoencephalography (MEG) to examine how the brain responds during attempts to recall information. The findings suggest that the brain can reactivate stored memories even when individuals are unable to consciously remember them. The research has been published in the Journal of Neuroscience.
Neural oscillations, often described as brain waves, refer to rhythmic electrical activity produced by the brain. These oscillations play an important role in encoding, storing and retrieving memories by coordinating activity among groups of neurons. Such rhythmic patterns are known to support memory formation, spatial navigation and episodic memory binding in the Hippocampus. Meanwhile, oscillations in the alpha and beta frequency bands are commonly associated with cortical processing during tasks involving long-term memory.
During the experiment, participants performed a paired-associates task designed to test memory recall. Each participant was asked to create a vivid association between a word and a video clip. Later, the same words were presented again and participants attempted to recall the corresponding video. Throughout the process, MEG recorded brain activity in real time. A machine-learning algorithm trained to identify the unique neural signature linked to each video was then used to determine whether the brain was reactivating a specific memory, even when participants were unable to consciously recall it.
The results revealed that the brain reactivated memories regardless of whether participants successfully recalled them. However, when a memory was consciously retrieved, the reactivated signal displayed stronger rhythmic fluctuations within the Alpha Wave frequency band. This rhythmic pattern appeared to help the memory signal stand out against the surrounding neural activity that might otherwise obscure it.
The study notes that the brain’s ability to reactivate the correct memory does not necessarily mean that the memory will reach conscious awareness. Instead, the findings suggest that rhythmic pulsing of the memory signal may help it emerge from background neural activity. A comparison described in the study likens this process to a stadium environment: when many people talk at once, individual voices are difficult to distinguish, but when a large group begins chanting the same song together, the sound becomes clear and noticeable. A similar principle may influence how the brain retrieves memories.
Researchers also observed that the rhythmic memory signal was accompanied by a reduction in overall sensory activity within the neocortex. This decrease in neocortical alpha power can be compared to background noise in a stadium becoming quieter. As the general noise level drops, even a small chant becomes easier to hear.
The findings may have important implications for conditions such as dementia. Many existing treatments assume that when individuals cannot recall a memory, the memory itself has been lost. However, if memories are still being reactivated within the brain but failing to reach conscious awareness, the results suggest that alternative treatment strategies may be needed. Instead of focusing solely on rebuilding lost memories, future approaches could concentrate on helping existing memories become accessible to awareness.
Reference
- Griffiths BJ. Alpha oscillations track the projection of reactivated memories into conscious awareness. J Neurosci. 2026 Mar 3. doi:10.1523/JNEUROSCI.1487-25.2026 PubMed PMID: 41781322.