Researchers Provide Explanation for Why Certain Memories Become Linked in the Brain

Engrams are collections of cells responsible for memory formation. These cells can be identified and manipulated in the laboratory but little was known about the exact mechanisms involved in memory development. In a recent study by The Hospital for Sick Children, researchers were able to show how engrams work, including the way separate memories can be linked together in the brain. The findings were just published in the journal Science.

Past research had shown that engram cells in the amygdala of the brain are responsible for retaining important memories. Little was known about how these cells actually work, however, and that was the focus of the most recent study. The research team analyzed the brains of mice during fear conditioning experiments and measured neuron activity in the lateral amygdala.

The researchers found that different groups of engram cells varied in excitability. When a new memory is being formed, the most excitable engrams “grab” and store that particular memory. Furthermore, these engrams stay in an excitable state for several hours. If another significant event occurs within that time window, about six hours, the same set of engrams will encode the new memory. The two memories are now linked in the mind because they’re being stored in the same neurons. The greater the distance between the two major events, the less likely they are to be linked. The researchers found that if the events happened 24 hours apart, the memories would be stored in different engrams and therefore not linked.

The team’s analysis provides a scientific explanation for why certain memories are linked together. If two traumatizing events happen in the same day, they are encoded by the same engrams and linked in the brain. This is why recalling one event may immediately cause a person to remember the other. These findings have important implications in mental health research. In some mental disorders, such as schizophrenia, memories become inappropriately linked or unlinked. By understanding exactly how engram cells work, we may be able to develop more effective treatments.


Asim J. Rashid et al. Competition between engrams influences fear memory formation and recall. Science (2016).

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