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Circuitry Of Fear Identified

November 11, 2010

Neurobiologists at the Friedrich Miescher Institute for Biomedical Research have identified, for the first time, clearly defined neural circuits responsible for the processing of fear states. These findings could ultimately help people suffering from post-traumatic stress disorder or anxiety disorders. The scientists’ results have been published in the latest issue of Nature.

Fear arises in the almond-shaped brain structure known as the amygdala. It is the amygdala which processes the strange noise, shadowy figure or scary face and not only triggers palpitations or nausea but can also cause us to flee or freeze. That much has long been known about the function of this part of the brain. What remains largely unclear, however, is precisely how fear develops, and which of the countless neurons in the amygdaloid region are involved in this process. But finding answers to these questions is vital for those who wish to improve the quality of life for people suffering as a result of traumatic experiences. In particular, patients with post-traumatic stress or anxiety disorders could benefit from the elucidation of neural processes in the amygdala.

Neurobiologists at the Friedrich Miescher Institute for Biomedical Research (FMI, part of the Novartis Research Foundation) have become the first to identify neural pathways and types of neurons in the amygdala which play a key role in the behavioral expression of fear. In two studies published in the latest issue of Nature, they show that there are clearly defined types of neurons in the amygdala which fulfill specific functions in the processing of fear inputs and subsequent fear responses. These cell types are organized in circuits, connecting neurons and various areas within the amygdala.

In collaboration with colleagues at the California Institute of Technology, the FMI neurobiologists went on to show that one of the cell types produces a signaling protein known as protein kinase C delta. This has provided the researchers with a marker for cells in the amygdala which directly regulate the expression of fear. They can now manipulate and study the behavior of these cells under a variety of conditions. Commenting on the relevance of their findings, FMI Group Leader Andreas Lthi, who led the study, said: “We now have at our disposal a molecular tool which should allow us to gain a better understanding of processes in the amygdala – and also of phobias and post-traumatic stress disorders.”

Lastly, the studies also revealed that these circuits play an important role in the generalization of fear. The same neurons are involved when fear becomes divorced from the original situation and becomes increasingly general. This may mean, for example, that some people’s feelings of claustrophobia in an elevator will develop into a fear of crowds and, finally, fear of leaving the house. Patients with disorders of this kind live in a state of constant anxiety, which remains difficult to treat.

Image Caption: Nerve cells in the amygdala

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