Living in Fear? Don’t Worry You can Learn Fearlessness

People who have been affected by a traumatic experience sometimes suffer from a long-lasting exaggerated ’fear response’. In such cases, the ’fear response’ is triggered by certain sensory impressions that occur in our everyday environment and which then can become overwhelming. Experts refer to this condition as post-traumatic stress disorder (PTSD). In this disorder, it is not possible, or only with difficulty, for affected individuals to unlearn the once-learned connection between a neutral environmental stimulus and the learned fear response, which impairs the success of therapies.

Knowing that the neurotransmitter serotonin plays an important role in the development of fear, the research team explored its role in extinction learning, i.e. the unlearning of fear, in greater detail.

To this end, they examined so-called knock-out mice that lack a certain serotonin receptor – the 5-HT2C receptor – due to genetic modifications. These mice learned in one day to associate a certain sound with a mild but unpleasant electrical stimulus.

As a result of this learning process, on the following day, they showed a fear response that was characterized by a motionless pause as soon as the tone was played, which we refer to as ‘freezing’.

In the next step, the researchers repeatedly played the tone to the mice without applying the electrical stimulus. Interestingly, they noticed that knock-out mice learned much faster than the tone does not predict the fear stimulus than mice who lacked this specific genetic modification.

The absence of Serotonin Receptors is an Advantage for Learning to be Without Fear

The researchers investigated this phenomenon in more detail and found that the knock-out mice showed changes in their neuronal activity in two different brain areas. One of these is a specific sub-region of the dorsal raphe nucleus (DRN), which is typically the main site of serotonin production in our brains.

In addition, they discovered aberrant neuronal activity in the so-called bed nucleus of the stria terminalis (BNST), which is a part of the so-called extended amygdala. The results also indicate a connection between the two brain regions, which leads the scientists to assume that an interplay is significant for improved extinction learning.

Possible Effect of Medication Revealed

The results of the study may reveal how drugs typically used in the treatment of PTSD affect the brain regions analyzed in this study. There are already drugs in clinical use that regulate the amount of available serotonin, so-called selective serotonin reuptake inhibitors, or SSRIs for short.

Taking these drugs over a prolonged period causes the relevant receptor to become less responsive to serotonin, similar to our knock-out model. Therefore, they assume that the changes they have described could be essential for the positive effect of SSRIs. They hope that their findings will help to develop more targeted treatment strategies for PTSD patients in the future.



Source-Eurekalert