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.
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