Scared Of The Monsters Hiding Under Your Bed? This Is How Your Brain Processes It All

Posted on April 28, 2014 in Health and Life

By Prabahan Chakraborty:

When I was three, ‘Jurassic Park’ had just been released in the theaters and was causing a sensation all around the world. The only theater near the campus where I stayed was lucky enough to get hold of a reel and screened it for weeks. One fine evening, as a result of rave reviews from neighbours and colleagues, my parents decided to take the tiny me along to a full house spectacle of CGI. The movie started and halfway into invasions by evil tyrannosauruses and velociraptors, I threw a crying fit so bad that my parents were forced to leave the show and return home. For days afterwards, every loud thud I heard in the distance would make me imagine a T-Rex just around the corner, and my mother would try to make me understand that it’s just a flyover being built.

Fancy scientists would call this ‘Ornithoscelidaphobia’, or the fear of dinosaurs.

For me, it was plain, simple and unadulterated ‘fear’. I was afraid and nothing else mattered. Period. Fear is, in fact, a part of our everyday life. We fear our bosses and our better halves (one more than the other though), lunatics and psychopaths and even restaurants whose food have histories of causing horrible dysenteries — as a matter of fact, any noxious element that has harmed me in the past or has the potential to harm me makes me afraid. It is a basic emotional response having an immense survival value, for it tells me to hold tight onto my pepper spray if I see a drunk approaching from the other end of the road. All animals experience fear — be it man or beast – a zebra, for example, is afraid when it sees a big cat approaching stealthily, and it sprints in an attempt to escape.

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Since the last few decades, there has been a significant interest into understanding how our brain interprets fear. To know how humans feel and react to fear, most scientists have preferentially turned to rats and mice instead and messed with them. Your primary goal while doing a study like this is to make the animal scared and to make a rat afraid, you would have to bring it in the vicinity of its ecologically relevant predator, probably a cat or a snake. There are people who do these sorts of crazy stuff, but as you might guess, these experiments would not be too feasible under lab conditions (imagine you being more afraid of the snake than the rat). So, what do we do?

It turns out the basic concept for an elegant solution to the problem was given by Ivan Pavlov, a Russian physiologist. In the early years of the last century, Pavlov did a path breaking experiment where he took a dog and gave it food. Introducing a twist, as the food was being served, he rang a bell such that the dog could hear it as smelling, seeing and thus, salivating in presence of the food. This went on for quite a few days. Interestingly, Pavlov saw that after a while, ringing the bell even in the absence of the actual food made the dog salivate. Somehow the memory of the food was tagged along with the memory of the bell so that one stimulus (the bell in this case, called conditioned stimulus- CS) was enough to elicit the response to another stimulus (the food, or unconditioned stimulus- US) which in itself does not cause any definite response. Taking this basic principle, what researchers did was fascinating. They took a rat in a chamber and gave it an electrical foot-shock (the US) while playing a tone (the CS) so that after some sessions of training, the rat started freezing in fear even when it heard the tone in absence of the shock. Freezing being a normal physiological response of a scared rat, one could easily quantify fear by measuring the time it froze for — the longer it remained still without even moving its whiskers, the more afraid it was. Simple.

This told us two things. One, it is possible to make a rat afraid in the lab. Two, you can get a quantitative estimation of its response (in this case time of freezing), which is the crux of any scientific method. But it had a major drawback — while we got to know about the external manifestation of fear, we had no clue what was going on inside its brain. Our brain consists of tiny units called neurons that communicate and talk to each other using electrical signals. Whatever we think, whatever processes and actions the brain dictates us to do, is nothing but a final output of complex series and parallel crosstalk between currents through these cellular circuits. So, to understand how the brain processes any information, you need to poke electrodes inside the brain which can pick up and record this current from neurons. The business of poking around gooey gray matter might seem disgusting, but pathological tests like EEG use the same principle, except the fact that it involves sticking electrodes on the surface of your skull, because though poking metal pieces inside a human brain is more fun, it nearly always lands you in jail.

So, a series of detailed experiments involving these recordings along with study of behaviour and brain images have revealed a region in the temporal lobe of the brain called the amygdala (from Greek amygdale meaning almond) which is the processing locus of our fear responses. The amygdala consists of several sub-regions, each of which play a distinct role in the process. The basolateral nucleus of the amygdala, for example, receives inputs from different senses that signal the presence of the fear stimulus. The signal then travels to the central nucleus which serves as the output zone. Like telephone cables connecting two different localities, the central nucleus then passes on the signal to other brain centres which cause the appropriate behavioural response. What’s stupefying is that all this detailed computation happens in the matter of milliseconds. The moment someone pranks you with a scary mask – you miss a beat. It is during this apparently negligible duration that a battery of different signals ram into your brain, is processed by your amygdala and scares the hell out of you. It would be wrong to assume, however, that the amygdala is the sole conductor of the elaborate symphony that is going on within your brain-box. It interacts with a number of different other regions which play their own part in this majestic score. The hippocampus and the prefrontal cortex are two such regions which not only are an intrinsic part of the network, but can also modulate it in their own way.

When the three-year-old-me was terrified by non-existent T-Rexs, I remember the fear having been there for quite a few days. With time, however, I became less afraid about these devilish reptiles, more so because my parents underwent a painful ordeal of showing me pictures of these monsters and explaining why they no longer invade gardens and supermarkets. In fact, for most of us, monsters under the bed vanished after they failed to show up repeatedly, right? Not surprisingly, even this is apparent erasure of the fear is modulated by the amygdala. It turns out that the original memory of fear can be overwritten by repeated exposure to the non-harmful conditioned stimulus (the sound of the bell in Pavlov’s and the tone in the rat’s experiments) which now can be rendered harmless. But there’s a catch. The memory is overwritten, not erased. All it takes for the original fear memory to jump back is a friend who dresses up as a zombie and hides under you bed on the first of April.

It goes without saying that all that we know about our brain, and indeed about fear, is just a fraction of the whole. There are infinite unanswered questions in the field that can be answered only with even more carefully designed experiments. The science of fear is not fearsome, so bravely venturing forth into its territory is the best option we have. As of now, we can only be gratified that evolution gave us the capability of getting afraid. Otherwise, we would have been wiped out long ago by pet panthers and king cobras. Trust me.

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