Working memory, that handy ability to consciously hold and manipulate new information in mind, takes work. In particular, participating neurons in the prefrontal cortex have to work together in synchrony to focus our thoughts, whether we’re remembering a set of directions or tonight’s menu specials. A new study by researchers based at The Picower Institute for Learning and Memory at MIT shows how that focus emerges.

The key measure in the study in Scientific Reports is the variability of the neurons’ activity. Scientists widely agree that less variability activity means more focused attunement to the task. Measures of that variability have indeed shown that it decreases when humans and animals focus during working memory games in the lab.

In several studies between 2016 and 2018 lead author Mikael Lundqvist and co-senior author Earl K. Miller showed through direct measurements of hundreds of neurons and rigorous modeling that bursts of gamma frequency rhythms in the prefrontal cortex coordinate neural representation of the information held in mind. The information representation can be measured in the synchronized spiking of populations of individual neurons. Bursts of beta frequency rhythms, meanwhile, implement the brain’s manipulation of that information. The theory, which Miller dubbed “Working Memory 2.0” challenged a long-held orthodoxy that neurons maintain working memory information through steady, persistent activity. Proponents of that older model, which emerged from averaged measurements made in relatively few neurons, used computer-based modeling of brain activity to argue that reduced variability cannot emerge from intermittent bursts of rhythmic activity.

But the new study shows that the reduced variability, does, in fact, emerge.

“We used actual neural activity recorded from the prefrontal cortex to show that the rhythmic bursts reduce their variability as animals focus on a task,” said Miller, Picower Professor in MIT’s Department of Brain and Cognitive Sciences.

“All the phenomena we think that is important working memory, the bursts of spiking the bursts of gamma are doing what they should do,” Miller said. “It’s all becoming more focused when the animals are performing a working memory task and that naturally reduces the variability. It shows how these new rhythmic elements of working memory are totally compatible with your brain focusing its activity on the task at hand.”

Direct observations

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