A research team, including Trinity’s Dr Tomás Ryan, has discovered a new form of short-term involving how context can heighten memory recall.
The research was carried out in Massachusetts Institute of Technology (MIT)’s Picower Institute for Learning and Memory and was published in the scientific journal Neuron. The study involved Ryan, an assistant professor in Trinity’s School of Biochemistry and Immunology and the Trinity College Institute of Neuroscience.
In a press statement, Ryan said: “We were in a position to discover this previously unknown behavioural phenomenon – a new form of short-term memory – only because our hypothesis was based on the time period revealed by a physiological analysis of the specific engram cells that store the memory. This integrative story highlights the value and importance of studying the biology of engram cells directly, and how careful physiology analysis can lead to new psychological insights.”
Nobel laureate Susumu Tonegawa, who is the current Picower Professor of Neuroscience at MIT and the senior author of this study, explained the findings in a press release: “Suppose you are driving home in the evening and encounter a beautiful orange twilight in the sky, which reminds you of the great vacation you had a few summers ago at a Caribbean island.”
He went on: “This initial recall could be a general recall of the vacation. But moments later, you may get reminded of details of some specific events or situations that took place during the vacation which you had not been thinking about.”
This secondary recall of more specific details involves a change in the electrical excitability of engram cells or the specific ensemble of neurons that together encode a given memory, seemingly through their unique network of connections.
The researchers showed that after mice formed a memory in a context, the engram cells encoding that memory in the brain would temporarily become much more electrically excitable if the mice were placed back in the same context again. Essentially, these cells became more excitable for about an hour when placed back in the same context again. The mice were also better able to distinguish between that context and distinct contexts even if they shared some similar cues.
From an evolutionary perspective, the increase in excitability allows them both to learn to avoid places where danger happened very recently and to continue to function normally in places that happen to have some irrelevant resemblance.
The specific change in the engram cells’ electrical properties has some direct implications for learning and behaviour that hadn’t been appreciated before. These brain structures and behavioural functions are conserved across all mammals, and so the discoveries can inform us of how short-term memory recall works in humans too.
