The chemistry of halloween and fear

With halloween just around the corner, we are at that time of the year where many of us get a thrill of being scared senseless. Some may love the boost of adrenaline that comes from watching a horror film or being spooked just before they go to sleep. But what is fear and why are some of us attracted to it?

Fear is the expectation or the anticipation of harm; the body is very sensitive to the possibility of threat and there are many pathways that can bring the signal of fear into your brain. For example if you are alone at night and hear a crash, the first initial sense of this is sound; the nerves in the ear pick up the information and the message is sent to the brain where it's then relayed to the thalamus which is part of a circuit linking the amygdala. 

The amygdala plays such a key role in the response to fear, as it's responsible for the release of several key Neurotransmitters in the body. Neurotransmitters are chemicals that nerve cells in the brain known as neurons use to communicate with each other in the nervous system. The most important of these neurotransmitters in the fear response is called glutamate. 

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The actions of glutamate in the amygdala in response to the 'crash' will then set of a number of other responses going. The information is relayed also to an area of the brain known as periaqueductal gray (PAG) which is an anatomic and functional interface between the fore brain and the lower brain stem. This is the region of the brain that is responsible for two classic responses of fear, freezing and jumping which are both very difficult to control. 

The information is also relayed to a region of the brain known as the hypothalamus; from here we get the fight or flight response. When the message is sent into the body from the hypothalamus it goes to the adrenal glands which pump out both cortisol and adrenaline. The adrenaline increases heart rate, blood pressure and respiratory rate which are key to our survival in a fear response scenario. The cortisol keeps the sympathetic nervous system up and running because this system is responsible for the fight or flight response sustaining that heightened sense of energy and alertness received from the adrenaline rush. 

Something to think about: watching a horror movie will be even more stressful without the organisation and down regulation of the amygdala  response. 

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