The ability to focus on a single idea without being distracted by the myriad thoughts, memories, sensations, and other stimuli constantly stirring in the human brain is known as “cognitive control.” While a well-functioning neural “filter” helps keep us on task, useful creative thoughts may get caught in the filter, as well. 

A research team led by Sharon Thompson-Schill, the Christopher H. Browne Distinguished Professor of Psychology in the School of Arts & Sciences and director of the Center for Cognitive Neuroscience, recently tested this theory via an experimental task designed to be easier when cognitive control is dialed back.   

In the experiment, participants were shown pictures of everyday objects and asked to quickly come up with out-of-the-ordinary uses for them, such as using a baseball bat as a rolling pin. Participants saw a sequence of 60 objects, one every nine seconds. The researchers measured how long it took for the participants to come up with a valid response, or if they were unable to do so before the next picture appeared.

“When you give people a task for which they do not know the goal, anything that they would normally do to filter out irrelevant information about the object will hurt their ability to do the task,” Thompson-Schill says.  

The researchers inhibited the left prefrontal cortex, one of the regions of the brain associated with cognitive control, using a technique called tDCS, or transcranial direct current stimulation. Participants wore a headband fitted with electrodes that passed a weak electrical current through their left prefrontal cortex.
The current makes it harder for neurons in the affected regions to fire, decreasing activity in that part of the brain, but only produces a slight tingling feeling. The relatively innocuous sensation enabled the researchers to test a placebo group, who didn’t receive any actual stimulation, as well as another control group who received it to a different region of their brains.

The groups who didn’t receive stimulation to their left prefrontal cortex missed, on average, 15 of the 60 responses, and, whey they did respond, gave answers in about five seconds. Participants who had their left prefrontal cortices inhibited only missed an average of 8, and responded a full second faster.

The results suggest that the brain’s filter can be a detriment in some situations, which may help explain why the prefrontal cortex takes so much longer to develop in humans than in any other primate.  

“There are things that are important to not filter, in particular when you are learning,” Thompson-Schill said. “If you throw out information about your environment as being irrelevant, you miss opportunities to learn about those things.”