Psychologists from Harvard Medical School, the University of Toronto, and the Rotman Research Institute at Toronto's Baycrest Centre for Geriatric Care compared the tested reaction times of 36 patients with specific lesions in the frontal lobes and other parts of the brain (caused by trauma, hemorrhage, surgery for benign tumors, and other acute disorders) with the reaction times of 12 control participants. In doing so, they were able to break down the once-monolithic concept of "attention" into at least three distinct processes that appear to be functionally and anatomically different.
The researchers looked at the speed, sensitivity and response biases of participants on different tasks (such as pressing a button when a "target" stimulus appeared), seeing how different people sped up or slowed down in the face of increasing distraction and redundant information. When the researchers analyzed response patterns, they saw that different types of attentional problems were associated with injuries in different parts of the brain. Thus, the researchers determined that attention may rest on at least three building blocks, each in a different part of the frontal lobes. The data complement prior, similar findings on the posterior (rear, not frontal) attentional system.
Led by Donald Stuss, Ph.D., of the Rotman Research Institute, the psychologists say that their findings support a proposed cognitive architecture of attention. The three "attentional systems" discovered (there may be more) in the frontal lobes include:
- In the superior medial (roughly, top middle) frontal regions, a system that helps us maintain a general state of readiness to respond. Patients with these lesions were slower to respond than other patients and the control participants.
In the left dorsolateral (front side) region, a system that sets our threshold for responding to an external stimulus. Patients with these lesions had trouble setting up the criterion levels, so they made errors primarily by considering most stimuli to be targets.
In the right dorsolateral region, a system that helps us both to attend to targets or stimuli defined by some individual schema (the criteria to which someone has to respond) and to inhibit responses to competing targets or stimuli. These patients could not effectively filter out competing stimuli, and responded erroneously at a significantly greater rate to both the desired and competing targets.
Because problems in sustaining attention to criteria -- in discriminating between what's important or not important -- are linked to lesions in this right lateral frontal region, the researchers speculate that this area is typically implicated in disordered attention. However, says Stuss, "a major impact of our research is that we can now separate much more specifically the types of attentional disorders, especially those related to the frontal lobes."
There are several practical implications, the most obvious being diagnostic. "If clinicians deal with attentional problems in a global sense," says Stuss, "they might not be addressing the specific problems of given individuals." At the least, he adds, the results provide hypotheses that can be directly questioned. "For example," he explains, "you could test whether a treatment approach is valid for all attentional disorders, or only specific ones."
In considering the multiple roles played by these different brain areas, the researchers note that lesions could also affect a variety of tasks that might not commonly be viewed as "attentional" -- such as verbal fluency, categorization and sequencing. The attentional disorders they describe, they write, "are only part of the complex sum of processes that define the role of the frontal lobes."
Stuss predicts that, "The real future excitement is the potential interactive complexity of the entire brain attentional system."
Article: "Dissociations Within the Anterior Attentional System: Effects of Task Complexity and Irrelevant Information on Reaction-Time Speed and Accuracy," Donald T. Stuss, Ph.D., Baycrest Centre for Geriatric Care and University of Toronto; Malcolm A. Binns, Ph.D., and Kelly J. Murphy, Ph.D., Baycrest Centre for Geriatric Care; Michael P. Alexander, Ph.D., Harvard Medical School and Baycrest Centre for Geriatric Care; Neuropsychology, Vol. 16, No. 4.
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Donald Stuss can be reached at the Rotman Research Institute, Baycrest Centre for Geriatric Care, by email at email@example.com, or by phone at (416) 785-2500 ext. 2918 or 2522.
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