Their work appears this month online in Psychophysiology.
"This study looks at two facets of anxiety that often are not distinguished," said U. of I. psychology professor Gregory A. Miller, co-principal investigator on the study with psychology professor Wendy Heller. "We had reason to think there were different brain mechanisms, different parts of the brain active at different times, depending on what type of anxiety one is facing."
According to a recent national survey, anxiety disorders are the most commonly reported psychiatric disorders in the U.S. The Diagnostic and Statistical Manual of Mental Disorders classifies nearly a dozen different anxiety disorders, from acute stress disorder to obsessive-compulsive disorder to panic attack and PTSD. But those who study and treat patients with anxiety disorders do not always differentiate the patients who worry, fret and ruminate from those who experience the panic, rapid heartbeat or bouts of sweating that characterize anxious arousal. These two kinds of anxiety may occur alone or in combination, with potentially important implications for treatment.
To test whether neural activation patterns supported the hypothesis that these two categories of anxiety are distinct, the researchers selected 42 subjects from a pool of 1,099 undergraduate college students, using psychological tests to categorize them as "high anxious apprehension," "high anxious arousal," or neither.
Other psychological assessments standardized the pool of participants by removing those with mood disorders or other complicating factors.
The researchers used functional Magnetic Resonance Imaging (fMRI) to map the brain areas with heightened neural activity during a variety of psychological probes.
As the researchers had predicted, the anxious apprehension group exhibited enhanced left-brain activity and the anxious arousal group had heightened activity in the right brain. The anxious apprehension group showed increased activity in a region of the left inferior frontal lobe that is associated with speech production. The anxious arousal group had more activity in a region of the right-hemisphere inferior temporal lobe that is believed to be involved in tracking and responding to information signaling danger.
Other studies using electroencephalographic (EEG) methods had found that patients diagnosed with generalized anxiety disorder and obsessive-compulsive disorder had heightened activity in the left brain, whereas patients with panic disorder, panic symptoms or those subjected to high stress situations exhibited enhanced activity in the right hemisphere.
This is the first study, however, to localize the affected regions to identify areas within each hemisphere that seem to matter.
Miller stressed the importance of a related finding: The researchers distinguished the left-brain region involved in anxious apprehension from a nearby structure that is associated with positive emotional processing."Left and right is not the only distinction we made," Miller said.
"This is biological validation of the proposal of the psychological differentiation of types of anxiety," Miller said. "Whether you want to treat anxiety psychologically or biologically - and we know that either type of intervention affects both the psychology and the biology of the person - these findings are a reminder that you might want to assess people carefully before you embark on a particular type of treatment."
This research is based on a master's thesis submitted by graduate student Anna S. Engels to the U. of I. The work was supported primarily by the National Institute of Mental Health and also by the National Institute on Drug Abuse, both at the National Institutes of Health. Support also was provided by the Beckman Institute, the department of psychology and the Intercampus Research Initiative on Biotechnology at the U. of I.
Miller is affiliated with the Beckman Institute; the department of psychology and the Neuroscience Program in the College of Liberal Arts and Sciences; and the department of psychiatry in the College of Medicine.
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