Research Hit: How Fear Can Get Stuck in the Brain
New research shows that generalised fear is caused by a chemical switch deep in the brain - which can be switched on and off
Can fear get stuck in the brain?
Well kind of - and this research published a few weeks ago explores this and has discovered the precise mechanism of this. Pretty important (very important actually!) but it has not been generally reported on I note.
What we are talking about is fear activation in the absence of any tangible threats such as is common in PTSD. It can also be considered a generalised fear.
Isn’t this the result of conditioning i.e. associating certain stimuli with fear?
That was one assumption and I reported on interesting research into those with susceptibility to PTSD last year. But this generalised fear is not the same as conditioning because it is not related to a trigger but rather a persistent underlying level of fear or anxiety.
Ok, so as you said the brain seems to get stuck in fear - so what is happening?
Hui-quan Li and colleagues of the University of California investigated the neural circuitry of fear in mice and ended up zooming in on a region in the brain stem called the dorsal raphe which is well connected to the amygdala (which is often considered the fear centre) and hypothalamus which is also related to stress hormone release.
So, not the famous amygdala but a region deeper?
Yes, if you read pop neuroscience articles, the amygdala is promoted as this emotional far and threat centre (it kind of is, but only kind of). But even more interesting is they discovered the neurotransmitter switch. They found that acute stress flips a switch which switches neurons from producing excitatory transmitters to producing GABA which is an inhibitory neurotransmitter (inhibitory only in the sense of brain signals not a particular emotion).
And is this responsible for this generalised fear response?
Yes, if these neurons in the dorsal raphe switch, then a generalised fear response ensues.
But this is in mice, right?
Yes, but they also analysed donated brain material from an individual who had PTSD and saw that this switch was also switched “on”.
And can we do anything about this?
Yes, to investigate the causality they tried two methods. One was to inject a virus into the brain stem that suppresses the gene responsible for synthesis of GABA. This inhibited the development of generalised fear. Also treating the mice immediately after a stressful event with the antidepressant fluoxetine (Prozac) seemed to block the development of generalised fear.
Ok, that sounds promising!
Yes, indeed very promising - it will be a while before this can applied in humans but having the knowledge of the precise mechanisms will open up all sorts of avenues for treating this.
Good Stuff!
Indeed, very good stuff!
Hui-quan Li, Wuji Jiang, Li Ling, Marta Pratelli, Cong Chen, Vaidehi Gupta, Swetha K. Godavarthi, Nicholas C. Spitzer.
Generalized fear after acute stress is caused by change in neuronal cotransmitter identity.
Science, 2024; 383 (6688): 1252
DOI: 10.1126/science.adj5996