Research into the nature of memory reveals how cells that store information are stabilized over time

Think of a time when you had two different but similar experiences in a short period. Maybe you attended two holiday parties in the same week or gave two presentations at work. Shortly afterward, you may find yourself confusing the two, but as time goes on that confusion recedes and you are better able to differentiate between these different experiences.

New research published in Nature Neuroscience published on January 19, reveals that this process occurs on a cellular level, findings that are critical to the understanding and treatment of memory disorders, such as Alzheimer’s disease.

The research focuses on engrams, which are neuronal cells in the brain that store memory information. “Engrams are the neurons that are reactivated to support memory recall,” says Dheeraj S. Roy, PhD, one of the paper’s senior authors and an assistant professor in the Department of Physiology and Biophysics in the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo. “When engrams are disrupted, you get amnesia.”

In the minutes and hours that immediately follow an experience, he explains, the brain needs to consolidate the engram to store it. “We wanted to know: What is happening during this consolidation process? What happens between the time that an engram is formed and when you need to recall that memory later?”

The researchers developed a computational model for learning and memory formation that starts with sensory information, which is the stimulus. Once that information gets to the hippocampus, the part of the brain where memories form, different neurons are activated, some of which are excitatory and others that are inhibitory.

When neurons are activated in the hippocampus, not all are going to be firing at once. As memories form, neurons that happen to be activated closely in time become a part of the engram and strengthen their connectivity to support future recall.

“Activation of engram cells during memory recall is not an all or none process but rather typically needs to reach a threshold (i.e., a percentage of the original engram) for efficient recall,” Roy explains. “Our model is the first to demonstrate that the engram population is not stable: The number of engram cells that are activated during recall decreases with time, meaning they are dynamic in nature, and so the next critical question was whether this had a behavioral consequence.”

Reference: Research into the nature of memory reveals how cells that store information are stabilized over time; Nature Neuroscience