New Study Finds That Fear Can Be Unlearned

New Study Finds That Fear Can Be Unlearned
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Serotonin is a neurotransmitter that plays an important part in both the beginning stages of fear and anxiety as well as the unlearning process. Dr. Katharina Spoida and Dr. Sandra Süß, both of the Department of General Zoology and Neurobiology in the Collaborative Research Center “Extinction Learning” at Ruhr University Bochum in Germany, have been leading a research team that has been looking into the underlying mechanisms. The researchers demonstrated that mice deficient in a particular serotonin receptor are able to unlearn fear far more rapidly than their wild-type counterparts.

The findings of this study offer a plausible justification for why medications that are conventionally prescribed for the management of post-traumatic stress disorder (PTSD) result in changes to the activity of our brains. Patients suffering from PTSD frequently have a diminished capacity to unlearn fear, which makes it more challenging to administer treatments.

Responses to danger are prompted by normal, daily stimuli.  Individuals who have been impacted by a traumatic event might occasionally experience a long-lasting excessive fear response. When this happens, the fear response is triggered by particular sensory impressions that happen in our daily life and which can then be unbearable. In these situations, the fear reaction is activated by certain sensations. Post-traumatic stress disorder is the name that specialists give to this condition (PTSD).

Because of this disorder, it is either impossible for affected individuals to unlearn the previously learned connection between a neutral environmental stimulus and the learned fear response, or it is only possible for them to do so with great effort. This hinders the ability of therapies to be effective.

The research team was aware that the neurotransmitter serotonin plays a significant part in the formation of fear, therefore they investigated the role that it plays in the learning process of extinction. These mice learnt in just one day to associate a particular sound with a gentle but nevertheless painful electrical stimulation. The next day, as a consequence of this learning process, they exhibited a panic response that was distinguished by a stationary halt immediately the tone was played. This behavior, which we term to as “freezing,” was observed in response to the tone.

The second thing that the researchers did was play the tone over and over again for the mice, but this time they didn’t use the electrical stimulus. Mice with a specific genetic mutation that was knocked out were able to learn considerably more quickly than control mice that the tone did not accurately predict the fear stimuli. As a consequence of this, it appears that the lack of a serotonin receptor confers a benefit for extinction learning.

After conducting additional investigation on this phenomena, the scientists discovered that knock-out mice displayed altered levels of neuronal activity in two distinct regions of their brains. One of these is a particular sub-region of the dorsal raphe nucleus (DRN), which is normally the primary location in our brains where serotonin is produced. In addition, the researchers found abnormal neuronal activity in the region of the brain known as the bed nucleus of the stria terminalis (BNST), which is a component of the region known as the extended amygdala.

The findings of the study also point to a link between the two brain areas, which has led the researchers to the conclusion that an interaction between the regions is necessary for enhanced extinction learning. Known side effects of the drug are shown here The findings of this study may provide light on how medications that are conventionally employed in the treatment of PTSD influence the areas of the brain that were under investigation in this particular study. The researchers have high hopes that their findings will one day contribute to the development of more specific treatment options for patients suffering from PTSD.


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Anna is an avid blogger with an educational background in medicine and mental health. She is a generalist with many other interests including nutrition, women's health, astronomy and photography. In her free time from work and writing, Anna enjoys nature walks, reading, and listening to jazz and classical music.

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