Illustration by Summer Renck By María Valerio Roa Have you ever watched a movie and felt super scared? Maybe even crying, shivering, and wanting to pee every time you see Coraline’s mom? Wait – I might have gotten a bit too personal there. Putting this out there before even starting: TMI Warning! We all have a certain movie that scares us, maybe even so much that it infiltrates our nightmares. This time of the year, those movies come to our mind. Whether it is The Conjuring, It, Coraline (my own favorite since 2009), or Hocus Pocus (let’s just say I won’t really understand you), we’ve all got that one movie that makes our heart pound (and not in the cute, butterflies in our stomach type of way). We know we feel this way due to fear, and that it takes many forms. We don’t only fear scary movies. We might fear the future, other’s opinions of us, or whether PrezBo is going to increase our tuition. But have you ever wondered what exactly causes these fears? I’m going to discuss why we fear, how it is manifested, and what exactly causes you to feel shivers down your spine. After all, emotions – including fear – can be explained through science. The Amygdala: Where Fear Originates The amygdala is one of the most studied areas of the brain. First recognized as a distinct brain region in the 19th century, the amygdala is an almond-shaped structure in the medial temporal lobe, composed of distinct sub areas, called nuclei. These nuclei are composed of neuronal cell bodies that give rise to many projections responsible for transmitting signals to other neurons. In total, the amygdala has thirteen nuclei. One interesting subregion of the amygdala is its lateral nucleus, known as the “gatekeeper”. The lateral amygdala receives most inputs from sensory systems responsible for vision, audition (hearing), somatosensation (eg: pain), olfaction (smell), and taste. In other words, the lateral amygdala is in charge of controlling our emotional reactions. Therefore, if when watching It, you see Pennywise’s face and scream, blame your amygdala! Although it receives most of the inputs from sensory systems, the amygdala is a relatively silent area of the brain. American neurologist Joseph Ledoux describes it as containing a “strong inhibitory network that keeps spontaneous cellular activity low and that prevents cells from firing action potentials to irrelevant stimuli”. Therefore, while the amygdala is in charge of controlling emotions, we don’t feel everything. Rather, we just feel stimuli that the brain considers relevant enough for us to feel. Therefore, we may fear some things but not others, because our amygdala might consider The Exorcist scary enough to make us cry but not necessarily No-Face from Spirited Away. The emotion that’s the most associated with the amygdala is fear. Now, you might be wondering… How exactly does the amygdala cause fear? The Molecular Mechanisms Behind Fear Like most (biological) things in the world, fear results from molecular mechanisms occurring in the brain. In short, during conditioning (when stimuli are linked together to produce a response), the lateral amygdala releases glutamate, an excitatory neurotransmitter, from its sensory fibers, which then binds to AMPA and NMDA, excitatory amino acid receptors. Glutamate is a polar, negatively charged amino acid. When it comes to contact with the APMA, glutamate gets depolarized (loses its polarity and gets inhibited with repetition). While APMA has a great effect on the glutamate released by the amygdala, the NMDA has little effect on it, as the unpolarized glutamate produced by APMA binding cannot remove the magnesium block on NMDA receptors. The magnesium flow block is removed by depolarizing the cell as a whole by an input such as electric shock around conditioning. The removal of the magnesium block allows enough calcium to enter the cell in order to maintain plasticity, which is the “ability of the nervous system to change its activity in response to intrinsic or extrinsic stimuli by reorganizing its structure, functions, or connections”. Plasticity is essential for memory processes. Therefore, the calcium entering the cell also helps maintain short-term memory. More calcium is needed for the enduring plasticity that supports long-term memory, however. This calcium enters through voltage-gated channels opened by shock stimulus. Protein kinases, enzymes that induce conformational changes in proteins by transforming them from their inactive to active form, such as MAP kinase, are activated by this input of combined levels of calcium and “trigger gene expression and protein synthesis”. These synthesized proteins then go back to the beginning and stabilize the connection with the initial inputs (glutamate and receptors). This is what causes us to fear, as APMA receptor protein synthesis plays a key role in the memory related to fear conditioning. We call this stabilization of memory through protein synthesis consolidation. Consolidation is a process in which “short-term memory (STM) is transformed, over time, into stable long-term memory (LTM)”. We associate fear with danger and, being humans, our goal is to survive. Therefore, fear is rapidly acquired and transformed into LTM, as it conveys information about “danger in the environment that may be important for survival”. Ultimately, whenever we watch a scary movie, all these brain mechanisms and protein synthesis occur to create a long-term memory that could alert us if something in the movie were to happen to us in real life. While very unlikely, our brain processes it as if we were experiencing it and records it as a traumatic event we should avoid. Adrenaline, goosebumps, and shivers Apart from detecting threats, when we see something we fear, the amygdala activates another part of the brain called the hypothalamus, “the forebrain territory that controls homeostasis and drives in vertebrates”. The hypothalamus then sends signals to the pituitary gland, which in turn send signals to the adrenal glands. Adrenaline or epinephrine, the hormone that controls the flight or fight response, gets released from the adrenal medulla located in the inner part of the adrenal glands. From this adrenaline rush, our heart rates accelerate. Hence, our hearts pound in the not cute, butterflies in our stomach kind of way. Our force of heart contractions also increases, which increases blood delivered to our muscles and brain, relaxes airway smooth muscles, and leads to quicker metabolism of glucose. Who would have thought that fear would have some positive effects? Certainly not Dorothy when she was walking around the forest full of lions, tigers, and bears, oh my! Fear also manifests itself through shivering, due to an adrenaline rush. However, the most notable effect of fear may be the surge of goosebumps in our skin. This is called the pilomotor effect, (spookily) also called “horripilation,” and “consists of involuntary hair erection induced by contraction of arrectores pilorum muscles, i.e., the tiny muscles located at the origin of each body hair”. So… in summary, what happens when I watch Coraline? Sorry… I meant to say scary movie When you watch Coraline, your amygdala gets activated, which in turn activates your hypothalamus, which in turn activates your adrenal glands, which in turn create all of the fun effects you sense when you are scared, such as goosebumps, shivering, and a pounding heart. Fear is your body’s reaction to danger. Therefore, when you sense fear by watching a movie you know it is because your body senses that what is on the screen could happen to you in real life, even though it is highly unlikely. Since you’re probably not going to get your eyes taken out and replaced with buttons or get converted into a cat for 300 years (...hopefully), I hope you watch Coraline and Hocus Pocus, eat candy corn, and that your amygdala does not get activated this season! Trick or Treat! Happy Halloween!
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