Specific memory is stored in several areas of the brain.

Neuroscientist Dheeraj Roy and his colleagues believe they can the most complete and rigorous evidence to date that engrams, sets of neurons that, through physical or chemical changes, retain the memory of an accurate memory, are interconnected in several areas.

Regions of the mouse brain involved in encoding certain memories.

Several areas of the mouse brain are involved in encoding specific memory (top). They are also involved in recalling memories upon reactivation (below).

Photo: MIT/Tonegawa Lab

So far, memory storage has mostly been associated with the hippocampus, amygdala, or cortex. More than a century ago, the German evolutionary biologist Richard Semon hypothesized the existence of unified engram systemsbut it was still impossible to verify this due to technological limitations.

Memory card

To test which areas of the brain are involved in recalling memories, an MIT team conducted a series of groundbreaking experiments in mice. She analyzed 247 regions of the brains of rodents who were moved from their home cage to another cage, where they were given a small but memorable electric shock.

In the first group, mouse neurons were modified to become fluorescent when they expressed a gene needed to encode memory, that is, to store information in the form of memories.

In the second group, the cells activated by the memory of the electric shock were fluorescently labeled. Two groups of rodents were compared with relatives of the control group.

Thus, neurons activated in both groups, either by memory encoding or by memory activation, could be observed under a microscope.

By comparing the brains of mice from the two groups, the researchers were able to exclude specific areas and map out 117 areas with a high probability of participating in memory.

Experiments have not only revealed significant reactivation of engrams in known areas of the hippocampus and amygdala, but have also shown reactivation in many other structures.authors write.

Using a computer to count the fluorescent cells in each sample, the researchers created whole-brain maps of regions with apparently high memory encoding or recall activity.

Scientists believe that by storing one memory in such a branched complex nervous system, the brain makes the memory more efficient and stable. They also found that memory or recall is more efficient when multiple areas of memory storage are reactivated rather than just one.

This new knowledge suggests that memory disorders can be treated.

If some memory disorders are due to dysfunction in the hippocampus or cortex, can we affect the cells associated with engrams in other areas? And could such a manipulation restore some memory functions? asks Dheeraj Roy, co-author of this study published in the journal. NatureCommunication (New window) (in English).

That’s just one of the questions researchers can explore now that the study has revealed a list of places where at least one type of memory is stored in the mammalian brain.

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