A team of researchers from MIT hasdiscovered a circuit in the brains of mice that, when stimulated, canprolong the effects of therapy designed to suppress fear-relatedphobias. The results of the study could lead to more effectivetherapy aimed at people suffering from debilitating phobias such asa fear of flying, and could even aid in the treatment of more complexdisorders such as post-traumaticstress disorder (PTSD).
According to the Anxiety and Depression Association of America, each year 18 percent of adults livingin the US are diagnosed as having some form of fear or anxietydisorder, with 19 million of them having a specific phobia.The leading method of dealing with extreme fears, such asarachnophobia, is a treatment known as exposure therapy.
During an exposure therapy session, apatient is exposed to anxiety-provoking cues relating to their phobiain a safe environment. For example, an individual terrified of flyingwould be shown various images of aircraft. The repetition of thistechnique eventually decreases the fear reaction related to thesecues, as the brain learns that nothing bad or painful will occur.
However, while the treatment is ofteneffective in the short term, individuals are likely to have theirphobias resurface through a phenomenon known as spontaneous recovery.
Advances in mankind's understanding ofthe human brain are gradually allowing us to discover certainconnections, or neural circuits, that are activated as the brainexperiences a particular emotion or state.
For some time, it has been hypothesizedthat such a circuit exists connecting parts of the brain that dealwith fear and reward as a patient experiences exposure therapy. Inorder to establish whether such a circuit was in play, and whether itcould be used to prolong the effects of the therapy, the researchersconditioned laboratory mice to fear a certain noise by subjectingthem to a foot shock each time the audio cue sounded.
With the anxiety established, the micewere then put through exposure therapy sessions, during which thenoise was sounded, and no shocks were administered. The researchersobserved that, as the therapy progressed, a neural circuit wasemployed in the brains of the mice, connecting the basolateralamygdala (BLA) which is associated with fear memory, and the nucleusaccumbens (NAc), which governs reward events.
The involvement of this connection,which the researchers dubbed the BLA-NAc circuit, suggested that thebrain interprets the lack of an expected painful or unpleasant eventas a kind of reward. Having established this link, the team testedthe effects of actively stimulating the circuit during therapy, byeither giving the mice a sugary drink as they heard the audio cue, ordirectly influencing the connection via flashes of light deliveredthrough an optical wire in mice that had been genetically modified to be receptive to such stimulation.
It was found that, for mice whoseneural circuit had been stimulated via the sugary drink reward, thatthe effects of the exposure treatment lasted 55 days longer than hadbeen the case for mice who had gone without stimulation. Micesubjected to bursts of light from the optical cable also benefitedfrom an increase in the amount of time that the fear reaction couldbe subdued.
The next step for the team from MIT isto understand how the circuit represses the fear response, and toidentify whether distinct sub-circuits are active over the course ofthe fear learning, and subsequent counterconditioning phases of thestudy. Such research could one day lead to improved treatments forthose suffering from debilitating phobias and PTSD.
A paper detailing the research was just published in the journal eLife.
Source: MIT
