Fear is a tricky subject. On one hand it is a protective emotion that uses our past experiences and warns us of potentially dangerous situations. In other cases however it can drive people to become scared of relatively normal things such as the outdoors, in the case of agoraphobia. Fear can also play an important role in psychiatric disorders like post-traumatic stress disorder (PTSD) and severe anxiety.
The neurology of fear like many emotions remains poorly understood. However new research into the connections between brain cells to better understand how we store information that leads to the feeling of fear may help us in developing ways to stop it.
The amygdala is a very important component of the brain when dealing with fear, as it is responsible for conditioned responses. A conditioned response is a type of learnt behaviour that is picked up from past experience, like with Pavlov’s dogs. This can also be applied to fear- if you walk down a dark ally and someone chases you, you’re not going to want to be doing it again anytime soon. In the amygdala groups of inhibitory interneurons work naturally with time to dampen down the fear response (this is known as fear extinction) by limiting the passage of signals between neurones involved in fear responses, such as basal amygdala cells and central nuclei cells.
So that’s all well and good, we feel fear then our brains recognise that the adverse stimulus has been removed and works to prevent us continuously feeling afraid. However the next time you are presented with that situation of fear, you feel just like you did when the first adverse stimulus occurred, this is known as fear relapse. I suspect that in early humans this was an incredibly helpful warning system of dangerous situations, however in our comfortable modern age we now fear all sorts of things some more reasonable than others. So do we still need this fear response and if we can find a way to prevent being afraid, should we?
The hippocampus also has implication in the fear response as it plays a role in converting short-term to long-term memories. It also helps us recall previous experiences to predict adverse events, with the aim of avoiding them. A mechanism has been observed that passes information of adverse stimuli via CA1 interneurons to other neurons in the process of forming memories and allows ‘fear learning’. Inactivating the CA1 interneurons, by an injection of a recombinant adenovirus, during a situation that would normally cause fear learning in mice was shown to prevent these types of memories being formed.
Preventing the formation of memories that cause us to be afraid of, whatever we are afraid of, might seem very appealing. Especially in the context of sever anxiety and other neurological disorders. This one is another topic that will inevitably divide people depending on their experiences and beliefs.
Some people might be said to have science-phobia, and be against ‘meddling’ with nature. Is this an irrational fear or have the scientific community given enough adverse stimulus to cause this fear response? One to ponder.
Lovett-Barron M, Kaifosh P, Kheirbek MA, Danielson N, Zaremba JD, Reardon TR, Turi GF, Hen R, Zemelman BV, & Losonczy A (2014). Dendritic inhibition in the hippocampus supports fear learning. Science (New York, N.Y.), 343 (6173), 857-63 PMID: 24558155
Maren S (2013). Putting the brakes on fear. Neuron, 80 (4), 837-8 PMID: 24267644