Memory mechanics: how young brains move from essential to episodic memory

Summary: Researchers have discovered key molecular mechanisms that shift children’s memory formation from general or “essential” to event-based or “episodic”. This change in memory formation usually occurs between the ages of four and six.

The study identified that maturation of inhibitory cells called parvalbumin (PV)-expressing interneurons, enveloped by a dense matrix called the perineuronal network, enables memory specificity and appropriately sized engrams.

This new understanding of memory development could unlock insights into conditions affecting the brain, such as autism spectrum disorders and concussions.


  1. The study reveals that as inhibitory cells in the hippocampus mature, memory shifts from general to specific, forming appropriately sized engrams.
  2. The research team was able to accelerate the development of the perineuronal network, creating specific episodic memories in juvenile mice.
  3. The findings could shed light on new insights into various conditions affecting the brain, from autism to concussion.

Source: Hospital for sick children

How does our brain become able to create specific memories? In one of the first preclinical studies to examine memory development in young people, a research team at the Hospital for Sick Children (SickKids) may have identified a molecular cause for memory changes in early childhood.

Event memories, also known as episodic memories, are what people traditionally think of when they hear the word memory: a memory tied to a specific context. For young children, however, memory is more general or “essential” type, and these general memories are usually not tied to a specific context.

In a study published in Science led by Drs. Paul Frankland and Sheena Josselyn, both lead scientists in SickKids’ Neuroscience and Mental Health program, researchers are identifying the molecular mechanisms underlying the switch from essential memory to episodic memory in mice.

The team notes that understanding this change, which typically occurs between four and six years of age in children, may inform new insights into research into child development and conditions that affect the brain, from spectrum disorders autism with concussion.

A parvalbumin interneuron (blue) surrounded by the perineuronal net. Credit: Hospital for Sick Children.

“Researchers have studied the development of episodic memory for decades, but thanks to the development of precise cellular interventions, we have been able to examine this question at the molecular level for the very first time,” says Frankland, who also holds a professorship of Canada Research in Cognitive Neurobiology.

Perineuronal Network Growth May Trigger Changes in Memory

In adults, memory traces (also called engrams) are made up of 10-20% neurons, but the overall size of these engrams is doubled in young children, with 20-40% of neurons constituting an engram supporting a memory. .

So why the change? The hippocampus, a part of the brain responsible for learning and memory, contains a variety of neurons, including a type of inhibitory cell called a parvalbumin (PV)-expressing interneuron.

These inhibitory cells limit engram size and allow memory specificity. The research team identified that as these interneurons mature, memory shifts from general to more specific and engrams form at the appropriate size.

Using viral gene transfer technology developed by Dr. Alexander Dityatev, head of the Molecular Neuroplasticity Research Group at the German Center for Neurodegenerative Diseases, researchers set out to dig deeper and explore the reason for this shift.

They found that as a dense extracellular matrix, known as the perineuronal network, grows around these interneurons in the hippocampus, the interneurons mature, changing the way our brains create engrams and store memories. .

“Once we identified the perineuronal network as a key factor in interneuron maturation, we were able to accelerate network development and create specific, rather than general, episodic memories in juvenile mice,” says Josselyn, PhD. a Canada Research Chair based on circuits. of Memory.

Inform new knowledge about brain function and cognition

While the team was able to trigger this change in memory type by accelerating the development of the perineuronal network, they also note that the reasons for the age difference between gist and episodic type memories should not be overlooked.

“When you think about what memory is for, it makes sense that a child’s memory works differently than an adult’s,” says Adam Ramsaran, Frankland Lab PhD student and first author of the study.

“At three, you don’t need to remember details. An essential type memory helps children build a broad base of knowledge that can become more specific as they grow and have more experiences.

Building on these molecular discoveries, the research team has accelerated the growth of the perineuronal network by providing an enriched environment for the formation of specific memories, a finding that helps inform ongoing child development research at SickKids and at the University of Toronto.

“Apart from memory development, we also found similar maturation-like mechanisms involved in different sensory systems in the brain,” Frankland says.

“The same brain mechanism can be used by several different brain regions for several different purposes, presenting exciting new opportunities for research and collaboration.”

Funding: This study was funded by Brain Canada, Canadian Institutes of Health Research (CIHR), University of Toronto, SickKids Research Institute, German Research Foundation, German Center for Neurodegenerative Diseases, National Institutes of Health ( NIH), the Natural Sciences and Engineering Research Council of Canada (NSERC), the Ontario Graduate Scholarship Program, the Ontario Trillium Scholarship Program, and the Vector Institute.

About this memory and neurodevelopment research news

Author: Jelena Djurkic
Source: Hospital for sick children
Contact: Jelena Djurkic – Hospital for Sick Children
Picture: Header image credited to Neuroscience News. Article image credited to Hospital for Sick Children

Original research: Access closed.
“A change in the mechanisms controlling the formation of hippocampal engrams during brain maturation” by Paul Frankland et al. Science


A change in the mechanisms controlling the formation of hippocampal engrams during brain maturation

The ability to form accurate episodic memories develops with age, with young children only being able to form essential type memories that lack accuracy. The cellular and molecular events in the developing hippocampus that underlie the emergence of precise, episodic memory are unclear.

In mice, the absence of a competitive neural engram allocation process in the immature hippocampus prevented the formation of sparse engrams and accurate memories until the fourth postnatal week, when the inhibitory circuits of the hippocampus mature.

This age-related precision change of episodic-like memories involved the functional maturation of parvalbumin-expressing interneurons in the CA1 subfield through the assembly of extracellular perineuronal networks, which is necessary and sufficient for the onset of competitive neural allocation, sparse engram formation, and memory. accuracy.

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