The areas of the brain where fragments of memory are stored and the mechanism which results in total recall has been uncovered by scientists. Their study shows that an overall event is stored in the hippocampus, while individual details in the prefrontal cortex.
The findings have 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, describes the phenomenon as “parallel memory processing.”
“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,” she explains in a statement per South West News Service.
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.
“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,” says Dr. Rajasethupathy.
They shed fresh light on the distributed nature of memory processing and recall which is less understood than storage. “The existence of separate storage and retrieval pathways in the brain suggests targeting of prefrontal recall pathways may be more therapeutically promising,” she adds.
In experiments, the team recorded and manipulated 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.
Afterwards, 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.
“This suggests there’s a dedicated pathway for memory recall separate from memory formation,” notes first author Nakul Yadav, a graduate student in the lab.
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 ageing populations. All drugs trials to date have failed.
Report by South West News Service writer Mark Waghorn
