Anxiety Response Affected by Brain Cells
> 7/11/2008 4:00:26 PM

In searching for a clearer understanding of anxiety disorders, many researchers have placed their focus on the amygdala, which is often highly active in individuals struggling with fear and anxiety. This month, a report in the journal Nature reveals new information about how the amygdala might contribute to anxiety. Using rats, researchers from Rutgers University discovered neural cells within the amygdala that exert a large influence over an individual’s ability to silence painful memories that can trigger the fear response.

To study anxious behavior in the rats, the researchers paired a specific stimulus, a loud noise, with a mild shock. After repeatedly experiencing this combination of events, the rats associated one with the other and exhibited fearful behavior upon hearing the loud noise alone. To extinguish this conditioned response, the researchers continued to present the loud noise without the associated shock, a process that caused the rats’ fear response to diminish over time.

The researchers then studied the rats’ brains, searching for a neural mechanism that might affect the extinction process. They identified neural cells within the amygdala, called intercalated neurons, that can suppress sensory information sent from the amygdala to the rest of the brain. This information, if not controlled, could trigger anxiety. Using a drug, the researchers eliminated these cells from half of the rats, and unlike normal rats, these rats continued to act fearfully in response to the loud noise alone.

The extinction process does not always work successfully in humans, and many individuals with anxiety disorders have difficulty dissolving the association between traumatic memories and fearful behaviors. Contextual clues also affect how the brain extinguishes behaviors, and a response that has been extinguished in one setting will reappear if the stimulus occurs in a different environment. This suggests that the extinction process does not eliminate the original memory but subdues its influence within a particular context.

In people with post-traumatic stress disorder, phobias, and other anxiety disorders, the brain may be unable to fully extinguish the painful memories of past fears and traumas, possibly because the intercalated neurons within their brain do not function well. Continued research may lead to the development of new treatments designed to target these cells. And as we learn more about the mechanisms that contribute to anxiety, we will be better able to help those who struggle with the debilitating consequences of persistent fear and traumatic memories.

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