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Scientists discover that memories form in two different areas of the brain

It has implications for Alzheimer's disease as drugs that target the latter may be more effective in boosting recall.

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By Mark Waghorn via SWNS

The areas of the brain where fragments of memory are stored and the mechanism which results in the total recall have been uncovered by scientists.

Memories form in two different areas of the brain, an overall event is stored in the hippocampus and individual details in the prefrontal cortex.

It has implications for Alzheimer's disease as drugs that target the latter may be more effective in boosting recall.

Corresponding author Dr. Priyamvada Rajasethupathy, of The Rockefeller University in New York, described the phenomenon as "parallel memory processing."

She said: "Conjunctive representations of an experience are stored in the hippocampus whereas the constituent features are represented in the anterior cingulate region of the prefrontal cortex."

After a wonderful dinner at a restaurant, it’s not just the food that leaves a trace in your mind.

The odors, the decor, the sound of the band playing, the conversations and many other features combine to make it unforgettable.

Reviving any detail alone may be enough to bring it all back - days, months or years later. The study found these impressions are put away - in the prefrontal cortex.

It ensures future exposure to any cue is sufficient to activate neurons - which then access the hippocampus for recall of the whole memory.

Dr. Rajasethupathy said: "These findings have implications for treatment of conditions such as Alzheimer's where the deficits are thought to be more related to memory recall than storage."

They shed fresh light on the distributed nature of memory processing and recall - which is less understood than storage.

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She said: "The existence of separate storage and retrieval pathways in the brain suggests targeting of prefrontal recall pathways may be more therapeutically promising."

In experiments, the US team recorded and manipulated the neural activity of mice as they encountered sights, sounds and smells while in an endless corridor in virtual reality.

The rodents were trained to associate rooms composed of different combinations of sensory cues as rewarding or aversive.

Afterward, nudged by a specific scent or sound - the mice were able to recall the broader experience.

They knew whether to happily expect sugar water or look out for an annoying puff of air.

The tests demonstrated the entorhinal-hippocampal pathway, a well-studied circuit, was essential for forming and storing the experiences.

Meanwhile, the individual sensory features were being shipped off to prefrontal neurons.

Later, when mice encountered particular sensory features, a different circuit was engaged.

This time, the prefrontal neurons communicated with the hippocampus to conjure the relevant global memory.

First author Nakul Yadav, a graduate student in the lab, said: "This suggests there's a dedicated pathway for memory recall - separate from memory formation."

It's hoped the findings in the journal Nature will force some revision of the dominant models of how memory consolidation occurs - offering hope of new therapies.

The number of dementia cases is expected to triple to over 150 million by 2050 because of aging populations. All drug trials to date have failed.

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