In the current issue of the scientific journal “PLoS Computational Biology”, Ioannis Vlachos (right) from Bernstein Center Freiburg and his colleagues offer an explanation of how fears that have seemingly been overcome, are in reality only hidden.

The reason for the persistency of fears is that, literally, their roots run deep. Far below the cerebral cortex lies the “amygdala” which plays a crucial role in fear processes.

Fear is investigated in mice by exposing them to a neutral stimulus, a certain sound, for example, and at the same time an unpleasant one.

This leads to the animals being frightened of the sound as well. Context plays an important role in this case. If the scaring sound is played repeatedly in a new context without anything bad happening, the mice shed their fear again.

It returns immediately, however, if the sound is presented in the original, or even a completely novel context. Had the mice not discarded fear after all?

The fact that fears can be “masked” has been known for some time. Two co-authors of thestudy discovered that two groups of nerve cells within the amygdala are involved in this process.

By creating a model of the amygdala’s neuronal network Vlachos and colleagues were ble to find an explanation for how such a masking of fears is implemented in the brain.

One group of cells is responsible for the fear response, the second for its suppression. Activity of the latter inhibits the former, preventing fear signals being transmitted to other parts of the brain.

Nevertheless,  change in their connections that resulted in an increased activity in the fear-coding neurons in the first place, is still present.

As soon as the masking by the fear-suppressing neurons disappears, for example by changing the context, these connections come into action again – the fear returns.

According to the scientists, insights can be transferred to  humans, helping to treat fear more successfully in the future.

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