Cellular mechanisms behind memory maturation as children age studied

New Delhi: Researchers have uncovered the molecular mechanisms in young children's brains underlying the change from general "gist"-like memories to specific episodic memories tied to a context as they age, through a study conducted in mice.

They said that this change, generally occurring between four and six years old in children, could help inform child development research and conditions affecting their brain such as autism spectrum disorder to concussion.

The research, led by Paul Frankland and Sheena Josselyn, both Senior Scientists in the Neurosciences & Mental Health program at The Hospital for Sick Children (SickKids), Toronto, Canada, is published in the journal Science.

An engram is a postulated biochemical change in the neural tissue that represents a memory.

Memory traces, or engrams, in adults are made up of 10 to 20 per cent of neurons. However, in young children, the overall size of these engrams are doubled, with 20 to 40 per cent of neurons that make up an engram supporting a memory.

Inhibitory cells in the hippocampus region of the brain, which is responsible for learning and memory, constrain the size of the engram and enable memory specificity. These cells are called parvalbumin-expressing (PV) interneurons. Interneurons are neurons that are found exclusively in the central nervous system.

The researchers identified in juvenile mice that as a dense extracellular matrix, known as the perineuronal net, developed around these interneurons in the hippocampus, the interneurons matured.

The memory was, thus, found to transition from general to more specific and engrams were formed at the appropriate size.

"Once we identified the perineuronal net as a key factor in interneuron maturation, we were able to accelerate the net's development and create specific episodic, rather than general, memories in juvenile mice," said Josselyn.

While accelerating the net's development, the researchers provided an enriched environment to allow for the formation of specific memories.

The team also noted that the reasons for the age difference between gist-like and episodic memories should not be overlooked.

"When you think about what purpose memory serves, it makes sense that a child's memory would function differently from an adult," explained Adam Ramsaran, a PhD candidate in the Frankland Lab and first author on the study.

"At three years old, you don't need to remember the specifics. A gist-like memory helps children build a large knowledge base which can get more specific as they grow older and have more experiences," said Ramsaran.

"Outside of memory development, we also found similar maturation-type mechanisms involved in different sensory systems of the brain," said Frankland.

"The same brain mechanism may be used by several different brain regions for several different purposes, which presents exciting new opportunities for research and collaboration," said Frankland.