A core system for the implementation of task sets

Jun 7 2006

Scientists have used data from scans of 183 subjects to identify brain areas that consistently become active in a variety of cognitive tasks, such as reading, learning a rhythm or analyzing a picture.

If the brain in action can be compared to a symphony, with specialized sections required to pitch in at the right time to produce the desired melody, then the regions highlighted by the new study may be likened to conductors, researchers at Washington University School of Medicine in St. Louis assert.

"They appear to be helping to determine which brain regions will contribute to a cognitive task and when those regions will play a part in that task," says lead author Nico Dosenbach, an M.D./Ph.D. student. "Every time you move from not working on a task to working on a task, these areas seem to become active."

The study, published in Neuron, highlighted three regions, the dorsal anterior cingulate and the left and right frontal operculum. The cingulate is found near the midline of the top of the brain; the opercula are at the base of the brain in both the left and right hemispheres.

"For years, when you looked at maps of what different parts of the brain do, the opercula have often been blank," notes senior author Steven Petersen, Ph.D., James S. McDonnell Professor of Cognitive Neuroscience; professor of neuroscience, of neurobiology and of radiology; and associate professor of neurological surgery. "We have been struggling to figure out what they do, and now these data suggest the opercula may be involved in the creation of what neuroscientists call a task set."

Task sets are plans for accessing different parts of the brain to achieve a goal, such as reading the word "dog," coming up with verbs associated with the word "dog" or determining the color of the letters in the word "dog."

Much of the human brain's power derives from what Petersen calls "flexible configuration of processing systems," or the ability to take one stimulus and process it in different ways to produce different feedback. Different parts of the brain have specialized abilities that can contribute in various ways to completion of different tasks. They just have to be lined up to play their part when their abilities are needed.

Other neuroscientists previously have implicated the cingulate in a variety of specialized cognitive tasks, Dosenbach notes, but the new analysis may change their thinking.

"It's a question of whether the cingulate has specific contributions to make in all these tasks, or whether it plays such a very basic role that its participation is almost always required," he explains.

The researchers' theories are reinforced by akinetic mutism, a condition that occurs in patients who suffer a lesion from stroke or surgery that includes the cingulate. To varying degrees, such patients are minimally active.

"If you give them a cup of coffee, they'll drink it, but they'd never ask for a cup of coffee," Petersen explains. "If you ask them how they are, they'll tell you, 'I'm fine,' but they won't tell you a story."

"They seem to have problems voluntarily entering a task state," Dosenbach says. "They can do tasks with very explicit instructions, but are much less proficient at what's called random generation tasks, such as coming up with random words. So there is some other evidence that the cingulate really is an important contributor to task sets."

The analysis was based on data from eight separate functional brain imaging studies conducted over the course of five years. According to Petersen, the volume of data provided by the different studies was essential to making sure that the areas highlighted in the analysis were contributing at a very basic level, rather than at the specialized level of a particular task.

"Some neuroscientists were certain what we should have found with this analysis, and they were concerned when we didn't find what they expected," he says. "But it's a huge dataset, and the results were very clear."

For example, one brain area thought likely to be active in creating task sets, the dorsolateral prefrontal cortex, did not become active as consistently as the cingulate and the opercula.

"We're not implying that this region isn't important," Petersen says. "In this study, though, it just didn't come up as consistently as the cingulate and the opercula."

Although many of the tasks in the eight studies were language-related (reading a word or naming verbs associated with a given noun, such as "bark" for "dog"), some were not. Subjects in one study had to tap their fingers in time to a rhythm. Another group had to judge the orientation of lines. A third group was asked to match short graphic squiggles. The non-linguistic tasks produced the same results, according to Petersen.

Petersen and his colleagues plan follow-up studies to further understand the roles of the cingulate and the opercula in creating task sets and to see if these regions have similar roles in children of various ages. They are also planning to use a new type of functional brain imaging to look at the connections between other brain areas and the cingulate and the opercula.