IF YOU’RE reading this on a train, while making a mental note of the shopping you need, watching for your stop and trying to ignore the motormouth in the seat to your left, your “working memory” is in full swing: it’s the mental space we use for dealing with the here and now, and it’s strongly linked to intelligence scores. Now a study claims to have found the parts of the brain responsible for deciding just what you let into your mental workspace – and what you ignore.
Working memory enables most people to pay attention to only three or four things at a time. One theory is that it is finite, and that some people simply have more available than others. Another is that a good working memory is distinguished from a poor one by the ability to filter out irrelevant stuff and focus on the pertinent information. In other words, some people just have more trouble ignoring distractors (see “Focus, focus, focus”). This idea is backed up by a 2005 study in which participants were asked to remember only red items shown on a screen, when blue items were being shown as well. They found that the better the volunteers were at ignoring the blue items, the better their working memory scores were, suggesting that an efficient working memory was related, at least in part, to the ability to stay focused and ignore irrelevant stimuli.
Now the parts of the brain with this “gatekeeper” role have been pinpointed by Torkel Klingberg and Fiona McNab of the Karolinska Institute in Stockholm, Sweden. The pair used an fMRI scanner to measure the brain activity of 25 volunteers as they prepared to filter out irrelevancies. For example, they were told that if a triangle cue appeared on the screen, they should prepare to ignore any yellow circles that follow it and, conversely, if a square cue appeared, they should prepare to remember any yellow circles that follow.
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The researchers found that two regions of the brain were active as the volunteers prepared to filter this information. One was the prefrontal cortex, which is known to be involved in a range of high-level, executive control processes and is also linked to intelligence. The other was the globus pallidus, part of the brain involved in initiating and regulating motor commands and other actions.
Klingberg says there was a positive association between the volunteers’ working memory (measured before the scans took place), the level of activity in the two brain areas during filtering, and their scores in the filtering tasks (Nature Neuroscience, ).
“They have pretty compelling data,” says Edward Awh of the University of Oregon at Eugene. He likens the basal ganglia – of which the globus pallidus is a part – to the working memory’s own nightclub bouncer. “If you have an exclusive nightclub with limited capacity, then you’ll want to have someone good on the door,” he says.
The Human Brain – With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.
