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Helping Old Brains Connect Related Memories

Probing into the brains of mice, scientists have found the pathway through which memories are linked over time; this has allowed the team to reconnect separate memories in older brains. The paper is published in the journal Nature.

UCLA neuroscientists artificially stimulated neurons to help the aging brain recapture connections between related memories. Credit: UCLA/Silva Lab

A team of neuroscientists artificially triggered neurons so that related memories are reconnected by the ageing brain. Photo credits: UCLA/Silva Lab.

One of the greatest problems that comes with age involves memory. The human is but at the mercy of degeneration throughout time. Thankfully, the new study might help people suffering from these age-related memory deficiencies.

The team of researchers from David Geffen School of Medicine at UCLA aimed at identifying the ways in which the brain would connect two memories, and they also wanted to determine whether time had any effect on this link. They used a tiny microscope to probe into the brains of mice to find out. Lead author, professor of neurobiology Alcino Silva, explains that neuroscientists have so far only focused on the creation and storage of single memories. However, memories do not occur individually in reality, says first author Denise Cai. The latter further explains that the formation of new memories is affected by the past experiences of the person which also assist him in forecasting expectation and in decision-making. This study is, therefore, different from the previous ones.

Using a Miniscope, the researchers looked into the brains of young mice to observe their cells ‘live’. The microscope illuminated the neurons firing while the mice would move about freely. These mice were put into three boxes at a time (one week apart for the first and second boxes, and five hours for the second and third ones) for 10 minutes; these boxes differed in fragrance, shape, lighting, and flooring. The mice would then receive a small shock at the level of their foot. Then, two days later, they were returned to all three compartments whereby they were expected to freeze in fear upon recognising the third box – and, this did, in fact happen. However, the mice also displayed this response in the second box which was not associated with any shock.

Silva explains this as meaning that the mice would transfer their memory pertaining to the shock in the last box to its experience in the second one just 5 hours before – this theory was confirmed when the team examined the neural activity of the animals: they found that the same brain cells associated with the shock in the third box also recorded the memory of the second box. This implies that the memories would become interrelated in the way that the brain would encode and store them: this is why the mice would remember another memory related in time when the recall of one memory was stimulated.

When this experiment was repeated in older mice, they only froze in the third box, and not in the other ones. This would mean that the memories were not connected by the brain in these mice: using the miniscopes, this was confirmed as the brains of the mice were not found to link the two memories; rather, each memory had its own neural circuit encoding it.

These series of experiments show that age leads to related memories not being connected by the brain. Now, can this be changed?

The team used a biological tool to excite neurones found in the memory centre of the brain to boost the ability of the elderly mice to connect their memories. This caused the mice to freeze as the younger ones did because, this time around, they were able to link the shock of the box to the other boxes. Therefore, increasing excitability appears to have reversed the age-related problem.

The team is currently carrying out tests of an FDA-approved drug to determine its effects on old mice’s ability to link memories.

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