Study Challenges Brain’s Mechanism Of Long-Term And Short-Term Memories

The long-held theory of human brain using different mechanisms for forming long-term and short-term memories has been challenged by a new study.

Neuroscientists from UCL assessed patients with amnesia for the research.

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In cases of amnesia, patients are unable to form long-lasting memories due to an injury to the hippocampi, a pair of brain structures located in the depth of the temporal lobes.

However, researchers observed that the patients were able to remember a phone number over short periods of time, as long as they were attentive.

Based on the examination, the researchers built a hypothesis that the hippocampus supports long-term but not short-term memory.

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However, the UCL study shows that this distinction has to be reconsidered.

The team continued their research and studied patients with a specific form of epilepsy called 'temporal lobe epilepsy with bilateral hippocampal sclerosis', which leads to marked dysfunction of the hippocampi.

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They asked the patients to try and memorize photographic images depicting normal scenes, for example chairs and a table in a living-room.

Their memory of the image was tested and brain activity recorded using MEG (magnetoencephalography) after a short interval of just five seconds, or a long interval of 60 minutes.

The researchers noted that short-term memory about more detailed aspects of the scene required the coordinated activity of a network of visual and temporal brain areas, while standard short-term memory drew on a very different network.

The coordinated activity of visual and temporal brain areas was disrupted in the patients with hippocampal sclerosis.

Professor Emrah Duzel, UCL Institute for Cognitive Neuroscience, said: "As we anticipated, the patients could not distinguish the studied images from new images after 60 minutes - but performed normally at five seconds. However, a striking deficit emerged even at five seconds when we asked them to recall the detailed arrangement of objects within the scenes.

"These findings identify two distinct short-term memory networks in the brain: one that functions independently of the hippocampus and remains intact in patients with long-term memory deficits and one that is dependent on the hippocampus and is impaired alongside long-term memory."

Nathan Cashdollar, UCL Institute of Neurology and first author of the paper, added: "Recent behavioral observations had already begun challenging the classical distinction between long-term and short-term memory which has persisted for nearly half a century. However, this is the first functional and anatomical evidence showing which mechanisms are shared between short-term and long-term memory and which are independent."

"They also highlight that patients with impaired long-term memory have a short-term memory burden to carry in their daily life as well."

The study has been published in PNAS.

Source-ANI
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