New Research Reveals How Fear Get Stuck in Brains
By LINKÖPING UNIVERSITY
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The research, conducted in rats, was published in the scientific journal Molecular Psychiatry. It provides new insights into the processes behind anxiety-related disorders and identified shared mechanisms of anxiety and alcohol dependence.
The ability to feel fear is critical for escaping life-threatening
circumstances and learning how to avoid them in the future. However, in certain
conditions, such as post-traumatic stress disorder (PTSD) and other
disorders linked to anxiety, the fear reactions become excessive and continue
even when they are no longer necessary.
This causes intense anxiety even if no danger is present,
resulting in disability for the individual afflicted. Researchers believe that
some people are predisposed to developing pathological fears, which are caused
by problems with how the brain processes fearful memories.
Some brain regions are especially important for processing fear-related memories. When threatened, the amygdala is activated and collaborates with parts of the frontal brain lobes, known as the “prefrontal cortex,” which are critical for emotion regulation.
“We know that the network of nerve cells that connects the frontal
lobes to the amygdala is involved in fear responses. The connections between
these brain structures are altered in people with PTSD and other anxiety
disorders,” says Estelle Barbier, assistant professor in the Center for Social
and Affective Neuroscience (CSAN), and the Department of Biomedical and
Clinical Sciences (BKV) at Linköping University, who led the study.
However, the molecular mechanisms involved have long remained unknown. The researchers in the current study have investigated a protein known as PRDM2, an epigenetic enzyme that suppresses the expression of many genes.
The researchers have previously found that levels of PRDM2 are lower in alcohol
dependence, and lead to exaggerated stress responses. In people, it is very
common for alcohol dependence and anxiety-related conditions to be present at
the same time, and the researchers suspect that this is caused by common
mechanisms behind these conditions.
In order for new memories to last, they must be stabilized and
preserved as long-term memories. This process is known as “consolidation”. The
researchers in the current study have investigated the effects of reduced levels
of PRDM2 on the way fear memories are processed.
“We have identified a mechanism in which increased activity in the
network between the frontal lobes and the amygdala increases learned fear
reactions. We show that down-regulation of PRDM2 increases the consolidation of
fear-related memories,” says Estelle Barbier.
The researchers have also identified genes that are affected when
the level of PRDM2 is reduced. It became clear that this resulted in an
increase in the activity of nerve cells that connect the frontal lobes and the
amygdala.
“Patients with anxiety disorders may benefit from treatments that
weaken or erase fear memories. The biological mechanism that we have identified
involves the down-regulation of PRDM2, and we currently do not have any way of
increasing it. But the mechanism may be part of the explanation of why some
individuals have a greater vulnerability to developing anxiety-related
conditions. It may also explain why these conditions and alcohol dependence so
often are present together,” says Estelle Barbier.
Reference: “An epigenetic mechanism for over-consolidation of fear
memories” by Riccardo Barchiesi, Kanat Chanthongdee, Michele Petrella, Li Xu,
Simon Söderholm, Esi Domi, Gaelle Augier, Andrea Coppola, Joost Wiskerke, Ilona
Szczot, Ana Domi, Louise Adermark, Eric Augier, Claudio Cantù, Markus Heilig
and Estelle Barbier, 21 September 2022, Molecular Psychiatry.
DOI: 10.1038/s41380-022-01758-6
The study was funded by the Swedish Research Council, Region
Östergotland, Stiftelsen Psykiatriska Forskningsfonden, the Wallenberg
Foundations, and the Knut och Alice Wallenberg Foundation.