A central aspect of human intelligence, our ability to focus depends on a working memory able to quickly pluck information from among myriad thoughts and worries. In a new study, investigators from Brown University find the brain uses the same grey matter for working memory as it devotes to planning motion.
Lead investigator, David Badre, a professor of cognitive, linguistic, and physiological sciences, says the brain tasks a part of the striatum called the caudate as well as part of the prefrontal cortex on the dorsal anterior premotor cortex. "In the immediacy of what we're doing we have this small working memory capacity where we can hang on to a few things that are going to be useful in a few moments, and that's where output gating is crucial," he said in a statement.
In experiments with 22 adult volunteers, investigators used magnetic resonance imaging to monitor brain activity as participants completed a working memory task, measuring also the speed with which the brain selected information from among competing interests and distractions. Volunteers were provided with four different versions of a similar test of working memory, allowing the scientists to discern — by studying the corresponding brain images — between the working memory’s input and output.
As explained by investigator Christopher Chatham, input involves placing information into working memory while output allows a person to select information necessary to complete a given task — such as sending a text while walking down a busy sidewalk.
In the testing, volunteers were presented with a context clue — a number — either before or after viewing a sequence of characters including alphabet letters or typographical symbols known as wingdings. By observing the contrasting imagery between the two different tasks, as well as a third control task, the investigators were able to accurately isolate how the brain places information into working memory and how that information is then selected for retrieval.
Naturally, the volunteers accomplished the tasks at varying speeds, which the investigators used to gauge the amount of cognitive work performed by the brain. In general, tasks in which the context clue followed the character sequence took longer to perform — the output of selecting information from within the working memory. Conversely, speed increased when the clue preceded the sequence as the brain placed information into the working memory.
"The division of labor that's specifically posited by these computational models is one in which there is a basically a context being represented in the prefrontal cortex that determines the overall efficiency of going from stimulus to response — like a route," Chatham said. "The striatum is involved in the actual gating of that flow of information," he said, "like traffic lights along the route."
Aside from adding to basic science, the work may also help psychiatrists to better analyze the behavior of patients with brain injury.
Source: Badre D, Frank MJ, Chatham CH. Cortisocostriatal Output Gating During Selection From Working Memory. Neuron. 2014