Working memory is a sort of mental sketchpad that allows you to accomplish everyday tasks. It also allows your mind to go from merely responding to your environment to consciously asserting your agenda. In a new study, researchers at MIT's Picower Institute for Learning and Memory and the Department of Brain and Cognitive Sciences shows that the underlying mechanism depends on different frequencies of brain rhythms synchronizing neurons in distinct layers of the prefrontal cortex (PFC), the area of the brain associated with higher cognitive function. As animals performed a variety of working memory tasks, higher-frequency gamma rhythms in superficial layers of the PFC were regulated by lower-frequency alpha/beta frequency rhythms in deeper cortical layers. The findings suggest not only a general model of working memory, and the volition that makes it special, but also new ways that clinicians might investigate conditions such as schizophrenia where working memory function appears compromised.
The current study benefited from newly improved multilayer electrode brain sensors that few groups have applied in cognitive, rather than sensory, areas of the cortex. Researchers realized that they could determine whether deep alpha/beta and superficial gamma might interact for volitional control of working memory. In the lab they made multilayer measurements in six areas of the PFC as animals performed three different working memory tasks. In different tasks, animals had to hold a picture in working memory to subsequently choose a picture that matched it. In another type of task, the animals had to remember the screen location of a briefly flashed dot. Overall, the tasks asked the subjects to store, process, and then discard from working memory the appearance or the position of visual stimuli. With these insights, the team has since worked to directly test this multilayer, multi-frequency model of working memory dynamics more explicitly, with results in press but not yet published.