You are sitting at your computer quietly reading this article when – BOOM! – there is a sharp loud noise behind you! You instinctively stop what you are doing, jump up, and turn to the source of the noise. You freeze where you stand, and your brain quickly assesses the danger of the situation. Although it may seem like a brief moment, your brain is processing a ton of information and trying to decide if you should run away or stay and fight!

Fear

These instinctive behaviors of the fight or flight response are remarkably well-preserved in all vertebrates, as are the physiological effects of fear. The sympathetic nervous system helps the body prepare for fight or flight by releasing adrenalin, increasing heart and breathing rates, increasing blood supply to the muscles, enhancing reflexes, and dilating the pupils. All these things happen without you being consciously aware of them! In stressful situations, you are also less sensitive to pain, so you can concentrate fully on the threat at hand. These complex feelings involve the activity of many areas of your brain, which are processed by the amygdalaA collection of nuclei found in the temporal lobe. The amygd... More.

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Have you ever noticed that you only figure out what startled you after you’ve already reacted? This is because the amygdala is able to process sensory information and initiate behavioral responses before the information reaches the awareness centers of the brain! The amygdala receives sensory information from two separate pathways: a short route and a long route. Like all sensory information, the message is first routed to the thalamusA subcortical structure that serves as a relay between senso... More. Then information is sent directly to the amygdala (short route), which produces a fast reaction to the situation. Other information travels from the thalamus through the cortex (visual, auditory, prefrontal, etc.) and then to the amygdala (long route). The cortex evaluates the situation, assigns it a meaning, and if the meaning is threatening, then the amygdala is informed and produces the appropriate response. This long route brings your awareness to the situation and tells you that you have been startled. These two pathways explain why pranks can be so funny! If it’s done right, the person reacts quickly (short route), and only after the information is processed by the cortex (long route) does he realize that it was not a real life-threatening situation, and he simply had a good scare!

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As Juan told us earlier this week, the amygdala is not the “fear center” of the brain, since people without amygdalae can still feel panic. Indeed, there are several other brain regions that provide input to the amygdala. The hippocampusStructure in temporal lobe that has many functions but is es... More, for example, is the memory center of the brain and provides contextual information to the amygdala. If you have experienced something similar in the past, then you have heightened anxiety to the present situation. Moreover, when you are frightened or experience some other significant emotional experience, your body’s adrenal glands release adrenalin, which has been shown to help encode memories to the hippocampus more effectively. That’s why you are so good at remembering things that are important to you or that trigger intense emotions.

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The amygdala also gets input from the medial prefrontal cortex, which is involved in the planning phase of the response, after the initial reflexive reactions, when you have to choose the best course of action to get you out of danger. While the amygdala is fully developed at birth, the prefrontal cortex does not mature until early adulthood. Because of this, children and adolescents do not always make rational decisions and cannot always control their emotions.

So, the next time your friend jumps out of your closet in a screaming ghost mask, you will probably jump up and yell, giggle at your fright, and think about how your amygdala just processed that entire scenario through the interaction of many brain regions!

~
References:

TheBrain.McGill.Ca

Images adapted from Jessica Peterson/Tetra Images/Corbis, Rob Lewine/Tetra Images/Corbis, Tom Chance/Westend61/Corbis, Jade/Blend Images/CorbisWikimedia CommonsViewZone, Rutgers.  

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Kate Fehlhaber

Kate graduated from Scripps College in 2009 with a Bachelor of Arts degree in Neuroscience, completing the cellular and molecular track with honors. As an undergraduate, she studied long-term plasticity in models of Parkinson’s disease in a neurobiology lab at University of California, Los Angeles. She continued this research as lab manager before entering the University of Southern California Neuroscience graduate program in 2011 and then transferring to UCLA in 2013. She completed her PhD in 2017, where her research focused on understanding the communication between neurons in the eye. Kate founded Knowing Neurons in 2011, and her passion for creative science communication has continued to grow.
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Kate Fehlhaber

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Kate graduated from Scripps College in 2009 with a Bachelor of Arts degree in Neuroscience, completing the cellular and molecular track with honors. As an undergraduate, she studied long-term plasticity in models of Parkinson’s disease in a neurobiology lab at University of California, Los Angeles. She continued this research as lab manager before entering the University of Southern California Neuroscience graduate program in 2011 and then transferring to UCLA in 2013. She completed her PhD in 2017, where her research focused on understanding the communication between neurons in the eye. Kate founded Knowing Neurons in 2011, and her passion for creative science communication has continued to grow.