Brain scans read memories

FORMATION of a memory is widely believed to leave a ‘trace’ in the brain – a fleeting pattern of electrical activity which strengthens the connections within a widely distributed network of neurons, and which re-emerges when the memory is recalled. The concept of the memory trace was first proposed nearly a century ago, but the nature of the trace, its precise location in the brain and the underlying neural mechanisms all remain elusive. Researchers from University College London now report that functional magnetic resonance (fMRI) can be used to decode individual memory traces and to predict which of three recently encoded memories is being recalled.

The new study, led by Eleanor Maguire of the Wellcome Trust Centre for Neuroimaging, builds on earlier work which demonstrates that fMRI can be used to predict simple mental states from brain activity. Last year, Maguire and her colleagues showed that it is possible to predict an individual’s position in a virtual reality environment from patterns of activity in the hippocampus, and researchers from Vanderbilt University showed that activity in the visual cortex can be decoded to predict which image is being retained in working memory. Even more remarkably, Japanese researchers have reconstructed visual images from brain activity, including novel ones that their participants had never seen before.

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Glimpsing memory traces in real time

MEMORY is one of the biggest enduring mysteries of modern neuroscience, and has perhaps been researched more intensively than any other aspect of brain function. The past few decades have yielded a great deal of knowledge about the cellular and molecular mechanisms of memory, and it is now widely believed that memories are formed as a result of biochemical changes which ultimately lead to the strengthening of connections between nerve cells.

It is, however, also clear that memories are not encoded at the level of single neurons. Instead, the memory trace is thought of as a flurry of electrical activity within a scattered population of cells. Yet, very little is known about how memories are encoded and retrieved by populations of cells. Using a new large-scale recording technique, researchers from the Medical College of Georgia have now directly observed, for the first time, the population-level activity associated with encoding and retrieval of memory traces.

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