Researchers at Columbia University Medical Center have found a 'safety circuit' in the brains of mice associated with the good feelings of safety and security. It is not yet known whether a similar circuit exists in humans.

"This work points to a second system – in addition to the brain's well-known fear circuits – that probably malfunctions in some people with anxiety disorders," says the study's lead author, Michael Rogan. "This opens up hope for other types of treatment that can act on your sense of safety and security."

The safety circuit may also improve understanding of addiction since it operates in the some of the same areas of the brain thought to be involved in addiction. "There's a feeling of invulnerability that comes with alcohol and other drugs," Dr. Rogan says. "Addicts frequently say, 'I had my first drink, and I felt safe for the first time,' so it may be that drugs of abuse artificially activate some aspect of this safety mechanism."

In the past, most research on anxiety has understandably focused on the circuits in the brain that deal with fear. "When someone goes to a psychiatrist in terror or grinding anxiety, the doctor doesn't think about the patient's happiness issues," Dr. Rogan says.

The neurobiology of happiness, though generally ignored by researchers, may be just as important in understanding and treating the disorders. "The missing part of our picture of anxiety is the good feelings associated with being safe and secure," Dr. Rogan says. "But positive emotions are harder to study in the lab than negative emotions like fear. How do you know when you've made a mouse feel safe and secure?"

In their experiments, the researchers conditioned mice to associate a particular sound with the knowledge that they were safe from danger (mild electrical shocks). They recorded the brain activity before and after hearing the sound.

In line with previous research, they found the sound led to reduced activity in the amygdala, a brain area associated with fear.

"Researchers have generally talked about safety in terms of a reduction of fear, and it's no surprise that we found that the safety sound reduces neural activity in the amygdala," Michael Rogan says.

However, they also found the sound led to increased activity in an area of the brain thought to be involved in motivation and reward -- the caudoputamen.

"Our results show there's more to the feeling of safety and security than the simple absence of danger," Michael Rogan says. "We have found that there is another part of the brain that is involved in calculating how much protection or shelter is in the environment. Shelter is something that is independent of the presence or absence of danger, and it contributes to a sense of well being."

Rogan is currently planning studies using humans to determine whether the same circuits exist in people.

"These findings support the idea that learning about safety and learning about danger are related but independent processes," wrote the researchers. "Our data suggest a partial overlap of these two processes for an auditory [safety signal], extending from sensory processing through early amygdala processing."

The researchers concluded that "It will be interesting to examine the distinction between the positive response to safety and responses to stimuli traditionally understood to have hedonic value, such as food and sexual activity. The neural and molecular genetic substrates of these mechanisms are likely to provide new targets for the treatment of a variety of psychiatric disorders involving anxiety, mania, anhedonia, and addiction, and a greater understanding of highly adaptive psychological characteristics such as resilience."