The mystery of memory

Scientists at Baycrest’s Rotman Research Institute have uncovered an important clue in the brain’s hippocampus that may help solve a longstanding neuroscience mystery about differences in memory ability between people.

The breakthrough finding, published in the Dec. 22 issue of Neuron, is considered an important advance in understanding why some people have better recollection memory than others. This type of memory is used to relive past events in detail.

A growing body of research has already shown that, among healthy young adults, the overall size of the seahorse-shaped memory centre does not predict an individual’s ability in recollection memory. But does some other aspect of its anatomy provide a clue?

According to this latest study, stronger recollection memory is predicted by a larger posterior region of the hippocampus when compared to the anterior region. The greater the size imbalance between a larger posterior region and smaller anterior region, the more likely an individual will have stronger recollection memory.

“Our results show for that the size of the posterior hippocampus, especially when expressed as a ratio to the size of the anterior hippocampus, reliably predicts recollection in healthy adults,” said Dr. Jordan Poppenk, who led the study at Baycrest as a graduate student in Psychology, with senior author and cognitive scientist Dr. Morris Moscovitch.

The researchers also found evidence that the functional connections, possibly related to memory consolidation, between the posterior hippocampus and other parts of the brain may underlie enhanced memory collection.

The study began with high-resolution brain scanning of 18 healthy young adults to collect anatomical MRI (magnetic resonance imaging) and functional MRI data, and taking measures of hippocampal volume and connectivity. Participants completed a test to measure their recollection memory ability. Better recollection was associated with a larger posterior hippocampus and a smaller anterior hippocampus. The overall size of the hippocampus did not predict recollection ability. This same overall pattern was found again in three separate studies conducted by other Rotman scientists and analyzed by the researchers — that involved 38 additional participants.

Brain scan shows the hippocampus area in colour. Red is anterior region and blue is posterior region.

Dr. Poppenk is now a post-doctoral research fellow at Princeton University in Princeton, New Jersey. The study was supported by the Natural Sciences and Engineering Research Council of Canada and a J.S. McDonnell Foundation grant. The journal Neuron is published by Cell Press.

Photo © steve greer

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