In Brief

At least three different parts of the brain's frontal lobes have different effects on how the brain performs attentional tasks, find Donald T. Stuss, PhD, and colleagues in the October issue of Neuropsychology (Vol. 16, No. 4). With Michael P. Alexander, MD, Malcolm A. Binns, and Kelly J. Murphy, PhD, Stuss examined how distracting information affected the reaction times of 25 people with brain lesions in specific parts of the frontal lobes, 11 with lesions outside the frontal lobes and 12 with healthy brains.

In a series of increasingly complex tasks, each participant pressed a button with their dominant hand when they saw a specific shape, the target, flash on a computer screen and pressed a different button with their other hand when any other shape appeared. By measuring the participants' reaction times and error rates, Stuss and his colleagues concluded that three out of the four brain areas they studied affected the patients' performance in different ways:

  • Patients with superior medial frontal lesions were slower to respond to target shapes than the other groups. This suggests that that the area is involved with the brain's readiness to respond.

  • Patients with left dorsolateral lesions made significantly more false-positive errors than the controls. In other words, while they seldom mistook a target for a distractor, they tended to think that most shapes were targets. The authors suggest that the region sets the correct threshold for responding to an external stimulus. Because these patients had damage in this area, their threshold for responding was incorrect--significantly higher than other groups.

  • Patients with right dorsolateral lesions responded incorrectly at significantly higher rates to both the target and distractor shapes, suggesting that these patients had difficulty deciding which shape was the target as well as filtering out the distractors, or perhaps deciding what characteristics were relevant.

  • Those with inferior medial frontal lesions performed about the same as the control group on all of the tasks, suggesting this area was not involved in the attentional skills studied.

"People used to talk about the frontal lobes as a generic functional system," says Stuss, but this research shows that "the system is extremely complex, made up of multiple, different functions or processes related to different frontal brain regions that have to contribute in different ways to perform even a very simple task like this."

Practically, the research suggests that there are different types of attentional problems. By determining which part of the frontal lobes is dysfunctional, practitioners could provide treatment and rehabilitation in a more targeted manner, suggest the researchers, who are all connected with the Baycrest Centre for Geriatric Care in Toronto.

"What we've done in essence is add building blocks to the cognitive architecture of attention, emphasizing the multiple roles of different regions of the frontal lobes in attention," Stuss explains, adding that other brain regions, including portions of the frontal lobes his team didn't study, contribute in different ways as well.

--D. SMITH