New Anxiety Circuit Found in the Brain
A great deal of time has gone into trying to understand the precise function of the brain in relation to anxiety. To date it is the amygdala that has received most attention. The amygdala is often considered the fear center of the brain, and although it is referred to in the singular, there are in fact two amygdalas, almond-shaped and about an inch in length, located in the mid-brain. Recently however a team of Caltech researchers has discovered a new brain circuit previously thought to act as a brake on anxiety.
The precise nature of anxiety has vexed scientists for years. Yet this is a pressing problem with a stated 18 percent of American adults thought to suffer from anxiety disorders. The Caltech team focused their efforts on an area of the brain called the lateral septum. This part of the brain has known implications to anxiety, but its purpose has previously been thought to act as a brake on the anxiety response because the neurons involved are known to be inhibitory.
What the research team discovered was that by activating neurons in the lateral septum, even for a very short time, they produced an anxiety response that continued for at least 30 minutes. This overturned previous assumptions about the role of the lateral septum dampening down anxiety but opened up new questions about how inhibitory neurons could possibly be causing an anxiety response.
The team had a hunch about what might be happening so they set about tracking the path of the impulses and discovered lateral septum neurons were making connections with another batch of inhibitory neurons in an area of the brain called the hypothalamus. The team was right. They had discovered something called a double-inhibitory mechanism where two negatives make a positive. The fact that the hypothalamus connections also linked to a third area of the brain called the paraventricular nucleus (PVN) involved in the release of the stress hormone cortisol and implicated in anxiety, effectively provided evidence of a new anxiety circuit.
The findings could have important implications for the development of more specific medications to treat anxiety. If, as previously thought, the lateral septum neurons were thought to inhibit anxiety, drugs may well have been developed to stimulate their activity. The obvious implication would have been an increase in anxiety symptoms.
Lead researcher Todd Anthony made the point that so few psychiatric drugs have been developed in the past half-century because so little is known about brain circuitry. He described the achievement as “a foothold onto a very big mountain.”
Todd E. Anthony, Nick Dee, Amy Bernard, Walter Lerchner, Nathaniel Heintz, David J. Anderson. Control of Stress-Induced Persistent Anxiety by an Extra-Amygdala Septohypothalamic Circuit. Cell, 2014; 156 (3): 522-536.