PET pictures produce a palette of anxiety.

PET pictures produce a palette of anxiety

Scientists are going with the flow -- blood flow, that is -- to illuminate how the brain generates anxiety and fear. When experiment volunteers are told they will soon receive a painful electric shock, blood flow surges in their temporal poles, located in both brain hemispheres at the tips of the temporal lobes just behind the eyes, according to a report in the Feb. 24 SCIENCE.

It remains unclear if this experimentally induced "shock" anxiety duplicates more common forms, such as the queasy feeling before a root canal operation. But the evidence suggests the temporal poles may be crucial in brain processes that tag situations with a sense of uncertainty, helplessness or danger, say psychiatrist Eric M. Reiman and his colleagues at Washington University School of Medicine in St. Louis.

"A final common pathway in the brain for both normal and pathological anxiety may involve the temporal poles," Reiman adds.

The investigators took positron emission tomography (PET) measurements of cerebral blood flow in eight healthy volunteers before, during and after anticipation of a painful electric shock. subjects were injected with water containing minute amounts of a radioactively labeled oxygen isotope. This tracer remains active in the body for only a few minutes. An array of tubes around the head picks up gamma rays emitted by the decaying isotope, and a computer transforms the information into color-coded images of blood flow.

Before-and-after data provided a baseline for blood flow and controlled for anxiety produced by the PET procedure itself. Subjects received a mild electric shock after the second PET measurement period.

Only the temporal poles showed significant blood-flow increases while subjects awaited the electric shock. Blood flow reflects the activity of discrete groups of brain cells.

Although a brain structure called the amygdala did not light up in the PET study, there is much evidence it plays an important role in anxiety production, Reiman notes.

He and his co-workers previously studied people with panic disorder, which is characterized by recurrent anxiety attacks. An infusion of sodium lactate launches an anxiety arrack in many panic disorder patients. PET images show that before lactate infusion these individuals have uneven blood flow and disturbed oxygen metabolism in the parahippcampal gyrus, another part of the temporal lobes. During a lactate-induced anxiety attack, blood flow increases in the temporal poles, the same regions implicated in nonpanic anxiety.

The parahippocampal gyrus information to the temporal poles, Reiman says.

While PET is a promising tool in the study of normal emotions, "we're going to have to develop creative new ways to induce emotions in the laboratory," Reiman says.