Brains link nearby memories through dendrites, study finds

A new study explains why memories formed close in time feel connected. Researchers found that memories are linked in the brain through dendrites, the spiny extensions of neurons. This research was conducted with mice, using advanced imaging techniques. When a memory forms, dendrites can capture new information shortly afterward. Lead author Megha Sehgal, from The Ohio State University, compares neurons to computers, with dendrites being small, independent computers. This discovery provides new insight into how our brains organize memories. Previous studies focused on single memories, but this research looks at how we create groups of memories. Sehgal emphasizes that memories are not formed in isolation; they are connected in a framework we use to make decisions. In experiments, mice were placed in two different environments in quick succession. When shocked in one environment, they showed fear in both, linking the two experiences. The study examined the retrosplenial cortex, a brain area important for spatial memory, and found that linked memories activated the same neuron groups and dendritic branches. The researchers studied changes at the dendritic level, revealing that new memories lead to the growth of dendritic spines—tiny structures where neurons communicate. Spines formed during the first memory were likely to attract new spines for subsequent, closely-timed memories. To further explore this connection, the team used optogenetics, a method to control neurons with light. By reactivating specific dendritic parts active during memory formation, they linked unrelated memories. This demonstrates the crucial role of dendrites in memory networks. The study not only sheds light on memory formation but also suggests new ways to understand memory disorders, like Alzheimer’s disease. Sehgal believes these findings could help develop therapies for such conditions. The study was co-led by researchers from UCLA and Hellas, and was supported by several health organizations and foundations.