New research reveals how the brain holds information in mind

MIT neuroscientists have published a key new insight on how working memory functions, in a study published in PLOS Computational Biology.

The researchers at The Picower Institute for Learning and Memory compared measurements of brain cell activity in an animal performing a working memory task with the output of various computer models representing two theories on the underlying mechanism for holding information in mind.

The results favored the newer theory that a network of neurons stores information by making short-lived changes in the connections, or synapses, between them, rather than the traditional theory that memory is maintained by neurons remaining persistently active.

The idea that brain cells maintain memories by constantly being “on” may be simpler, but it doesn’t accurately represent the sophisticated flexibility of thought that can arise from intermittent neural activity supported by short-term synaptic plasticity.

The researchers found that only computer models that allowed for synapses to change connections transiently, known as “short-term synaptic plasticity,” produced neural activity patterns that matched what was observed in real brains during the working memory task. This suggests that “plastic” neural network models, which are more brain-like and have additional functional benefits in terms of robustness, may be the key to understanding how working memory works in nature.

“You need these kinds of mechanisms to give working memory activity the freedom it needs to be flexible,” said Earl K. Miller, Picower Professor Neuroscience in MIT’s Department of Brain and Cognitive Sciences (BCS). “If working memory was just sustained activity alone, it would be as simple as a light switch. But working memory is as complex and dynamic as our thoughts.”

Co-lead author Leo Kozachkov, who earned his PhD at MIT for work including this study, emphasized the importance of matching computer models to real-world data in determining how working memory information is held in mind and how nature actually does it. Senior author Earl K. Miller, Picower Professor of Neuroscience in MIT’s Department of Brain and Cognitive Sciences, added that short-term synaptic plasticity is crucial in giving working memory activity the flexibility it needs to be dynamic, like our thoughts.

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