One of the ways we learn and remember is by picking up on the timing and order of events—essentially, understanding what tends to happen next based on what just happened. This ability helps us make sense of the world and predict the future. Until now, most of what we know about how the human brain does this has come from brain scans, which show broad patterns of activity but can’t measure the activity of individual brain cells.
In this project, we were able to go a step further by recording signals from single neurons in people who already had electrodes implanted in their brains for medical reasons. We found that specific brain cells in the hippocampus and entorhinal cortex—areas important for memory—adjusted their activity to reflect the order of images shown in a complex sequence. Remarkably, people learned this sequence without being told to, and the brain's representation of the pattern stayed even after the sequence stopped.
The activity of these neurons not only mirrored the structure of the sequence but also predicted what was likely to come next. Additionally, during rest, the brain appeared to replay parts of the sequence quickly, as if reviewing or rehearsing what it had learned.
These results suggest that individual brain cells in memory-related areas help us build lasting, predictive mental maps of our experiences—capturing both what happened and when it happened.
Full text:
Tacikowski, P., Kalender, G., Ciliberti, D., & Fried, I. (2024). Human entorhinal and hippocampal neurons encode a temporal structure of experience. Nature, 635: 160-167. (PDF)
An example of structured experience: a sequence of events (1–3–5–...) that follows a random walk on a graph.