Research published April 22nd in the journal Neuron offers a better understanding of the neural circuits that control fear. The study focused on a group of cells in a part of the brain called the amygdala that the scientists say are likely important for learning to fear certain stimuli.

The amygdala is the brain's center for fear processing. It integrates incoming signals about potential threats and alerts the rest of the brain to the danger. The body responds with physiological changes such as an increase in heart rate and muscle tension. A critical part of the amygdala's job is to learn to identify situations in which the fear response is appropriate to the level of threat or danger. Consistently getting it wrong can be a sign of anxiety disorders or phobias.

In the new study, the researcher was led by 2009 NARSAD Young Investigator grantee Ingrid Ehrlich, Ph.D., a neuroscientist at the University of Tübingen in Germany. Dr. Ehrlich and her team focused on cells in the amygdala called mpITCs (medial paracapsular intercalated cells). Previous research had suggested these cells are involved in quieting the amygdala's output when signals from other parts of the brain indicate that fear should be suppressed. The new work shows that mpITCs are modified by fear learning and that the mpITCs have multiple pathways for dampening fear responses.

Dr. Ehrlich and the team traced mpITC connections to other cells in the amygdala and examined how those connections changed when animals learned to associate a simple auditory cue with an unpleasant experience. They also examined how the connections were changed by subsequent experiences that taught the animals to separate the auditory stimulus from the unpleasant encounter––a process known as fear extinction. The researchers tested the effects on cell-to-cell signaling both to and from the mpITCs.

They found that sensory input activated the mpITCs, and that this, in turn, inhibited output from the basolateral amygdala, another part of the amygdala that drives fear responses. The scientists showed that the strength of these connections can be altered by fear learning. They also discovered that neurons in the basolateral amygdala not only receive signals from the mpITCs, but also send signals back to them, reinforcing the fear-suppressing effects of the circuit. The findings suggest mpITCs may be particularly important in the regulation of fear learning and fear extinction.

Read the abstract.