Brain circuit can tune anxiety

August 21, 2013 by Anne Trafton
The tips of long neuronal extensions from the amygdala (blue) contact neurons of the hippocampus (green). This communication pathway helps to modulate anxiety. Credit: Ada Felix-Ortiz

Anxiety disorders, which include posttraumatic stress disorder, social phobias and obsessive-compulsive disorder, affect 40 million American adults in a given year. Currently available treatments, such as antianxiety drugs, are not always effective and have unwanted side effects.

To develop better treatments, a more specific understanding of the that produce is necessary, says Kay Tye, an assistant professor of brain and cognitive sciences and member of MIT's Picower Institute for Learning and Memory.

"The targets that current are acting on are very nonspecific. We don't actually know what the targets are for modulating anxiety-related behavior," Tye says.

In a step toward uncovering better targets, Tye and her colleagues have discovered a communication pathway between two brain structures—the amygdala and the ventral hippocampus—that appears to control anxiety levels. By turning the volume of this communication up and down in mice, the researchers were able to boost and reduce anxiety levels.

Lead authors of the paper, which appears in the Aug. 21 issue of Neuron, are technical assistant Ada Felix-Ortiz and postdoc Anna Beyeler. Other authors are former research assistant Changwoo Seo, summer student Christopher Leppla and research scientist Craig Wildes.

Measuring anxiety

Both the hippocampus, which is necessary for , and the amygdala, which is involved in memory and emotion processing, have previously been implicated in anxiety. However, it was unknown how the two interact.

To study those interactions, the researchers turned to optogenetics, which allows them to engineer neurons to turn their electrical activity on or off in response to light. For this study, the researchers modified a set of neurons in the basolateral amygdala (BLA); these neurons send long projections to cells of the ventral hippocampus.

The researchers tested the mice's by measuring how much time they were willing to spend in a situation that normally makes them anxious. Mice are naturally anxious in open spaces where they are easy targets for predators, so when placed in such an area, they tend to stay near the edges.

When the researchers activated the connection between cells in the amygdala and the hippocampus, the mice spent more time at the edges of an enclosure, suggesting they felt anxious. When the researchers shut off this pathway, the mice became more adventurous and willing to explore open spaces. However, when these mice had this pathway turned back on, they scampered back to the security of the edges.

Complex interactions

In a study published in 2011, Tye found that activating a different subset of neurons in the amygdala had the opposite effect on anxiety as the neurons studied in the new paper, suggesting that anxiety can be modulated by many different converging inputs.

"Neurons that look virtually indistinguishable from each other in a single region can project to different regions and these different projections can have totally opposite effects on anxiety," Tye says. "Anxiety is such an important trait for survival, so it makes sense that you want some redundancy in the system. You want a couple of different avenues to modulate anxiety."

In future studies, the MIT team plans to investigate the effects of the on other targets in the and the prefrontal cortex, which has also been implicated in anxiety. Deciphering these circuits could be an important step toward finding better drugs to help treat anxiety.

Related Stories

In the brain, broken down 'motors' cause anxiety

February 7, 2013

When motors break down, getting where you want to go becomes a struggle. Problems arise in much the same way for critical brain receptors when the molecular motors they depend on fail to operate. Now, researchers reporting ...

Recommended for you

Take a trip through the brain (w/ Video)

July 30, 2015

A new imaging tool developed by Boston scientists could do for the brain what the telescope did for space exploration. In the first demonstration of how the technology works, published July 30 in the journal Cell, the researchers ...

Surprising similarity in fly and mouse motion vision

July 29, 2015

At first glance, the eyes of mammals and those of insects do not seem to have much in common. However, a comparison of the neural circuits for detecting motion shows surprising parallels between flies and mice. Scientists ...

Research grasps how the brain plans gripping motion

July 28, 2015

With the results of a new study, neuroscientists have a firmer grasp on the way the brain formulates commands for the hand to grip an object. The advance could lead to improvements in future brain-computer interfaces that ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.