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THE AMYGDALA AND THE HUA MOUNTAIN

Updated: Aug 20


Image by Robina Weermeijer

See an image of the amygdala at Brainfacts.org:

https://www.brainfacts.org/3d-brain



The Hua Mountain of Shaanxi Province boasts one of the steepest cliffs in China but, despite the danger, many tourists access the Hua Shan plank walk every year. Even watching a video of someone 'walking the plank' is enough to cause light-headedness; the real experience is certainly not for the faint-hearted. Watching footage, never mind doing the climb, is likely to activate your amygdala. The amygdala is a sub cortical structure, located deep inside the temporal lobe. Its function is to signal to the brain when there is an emotional stimulus in the environment. This stimulus could be a threat (a road rage argument) or it could be sentimental (the ending of a sad film).


Let's say that watching a video of the Hua Mountain Climb is as close as you want to get. Once you see the long drop from the mountain, and imagine standing on the rather thin plank, your amygdala sends signals to your prefrontal cortex to indicate that there is a threat. Your prefrontal cortex might suppress the signal on the grounds that it is only a video and not the real thing. Still, that might not stop your heart rate from increasing and feeling butterflies in the stomach: this is because the amygdala has also signalled to your autonomic nervous system, which reacts to the height of the mountain, as though it is a real life experience.



THE CORTEX


The amygdala has an interactive relationship with the prefrontal cortex. LeDoux argued that the amygdala receives signals via a ‘low’ (subcortical fast) and a ‘high’ (cortical slow) route (LeDoux, 1998, p.165). The prefrontal cortex can supress signals from the amygdala, which is why a frightening experience might be much scarier the first time than on subsequent occasions. Some climbers of the Hua Mountain film themselves calmly holding onto the railing with one hand or dangling a leg over the side. It is likely that this is not their first time climbing such a mountain! On the first occasion, even for those who enjoy an adrenaline rush, it is probable that the amygdala is active. By the time that a climber can hold onto the side with one hand, it is likely that the prefrontal cortex has suppressed the threatening signal from the amygdala. Although accessing this path is terrifying to most people, a few risk-takers remain calm. The prefrontal activation can reason that the threat is under control, and the prefrontal cortex has, in effect, become more powerful than the amygdala.


The amygdala does not only signal to the prefrontal area. It has neural connections with the hippocampus, forming two key elements of the limbic system. The hippocampus stores long term memory. When the amygdala activates the hippocampus, it stimulates previously learned memories about frightening events. Is the threat familiar? What contextual memories exist of the threat? The hippocampus would store details about the Hua Mountain that might be relevant, such as being harnessed to a rope is a safety feature that makes the situation less threatening.


The amydgala also signals to the hypothalamus, which regulates functions such as feeding, fighting and fleeing. Climbing down a mountain requires extra oxygen and the hypothalamus can stimulate the adrenal gland to stimulate the release of adrenaline, which in turn will increase heart rate and blood pressure. In the case of climbing the Hua Mountain, raised heart rate might make the individual feel more scared, but if the threat in question happened to be a predator, then raised heart rate would help to run away.



AGGRESSION


Imagine for a moment that an individual’s amygdala had been removed before climbing the Hua Mountain. The effect is likely to be a reduced sense of the possible threat of the steep drop. Even someone terrified of heights would behave quite differently without an amygdala. In research using animals, when the amygdala is removed, the result is decreased aggression (Sapolsky, 2017, p.31). When human participants are awaiting an electric shock, their amygdala activates in anticipation (p. 34). In a more social context, the Ultimatum Game demonstrates the amygdala’s involvement in moments of perceived injustice. Participants play a game in which they receive monetary offers, whilst undergoing fMRI scans. When a participant is about the reject a derisory offer, their amygdala experiences greater activation (Gospic, 2011).


The amygdala is also implicated in conditioned fear. This is where the individual shows a fear response when a given trigger is available. For some individuals, who fear heights to such an extent, the sight of a lift might be enough to trigger an anxious response. Imagine that an individual has a fear of heights after being taken to the top of the Eiffel Tower when young. To get to the top, tourists take a lift. Maybe a lift is now a conditioned stimulus because it has become associated with heights. When individuals have post traumatic stress disorder environmental stimuli, which could be any ‘banging’ sound, triggers a fear response. The amygdala has become conditioned to fear the stimulus.



SCHIZOPHRENIA


Schizophrenia is a condition which partly involves fear. One common symptom is paranoia which is, in a way, a heightened state of fear. Le Doux makes a case for the contribution of the amygdala to anxiety-related disorders more generally. The subcortical and cortical route to the amygdala could explain why individuals with anxiety-related conditions are more prone to fear responses. If the subcortical route is stronger than the cortical one, the individual’s amygdala will be more prone to activation in a way which is less likely to be within conscious control. Whereas a conscious signal, via the cortical route, is a fear response which might be rationalised. The idea is that anxiety is the consequence of too much sub cortical activation. At least when the amygdala is stimulated via the cortex the relative slowness offers the opportunity to avert or mediate the threat. The symptoms of schizophrenia therefore can be understood by looking at the subcortical or faster route to amygdala activation (LeDoux, 1998, p.252-6).


Meanwhile, researchers have noted that the amygdala has a smaller volume in schizophrenics. Changes to the amygdala inevitably affects changes to signals received in the prefrontal cortex. In his later book, LeDoux discusses the work of Grace who claimed that schizophrenia symptoms are the result of changes to the circuitry involving the amygdala, hippocampus, prefrontal cortex and nucleus accumbens. A smaller amygdala will affect how the prefrontal cortex controls decision-making (LeDoux, 2002, p.272). It is a reminder that an amygdala is necessary for processing emotion, and does not simply cause unwanted emotional reactions. Without a functioning amygdala, the prefrontal cortex is working with unreliable signals which might underrepresent a serious threat.



References


Brainfacts.org hosts the interactive brain which is powered by the Wellcome Trust and developed by Matt Wimsatt and Jack Simpson


'Limbic Justice - Aygdala Involvement in Immediate Rejection in the Ultimatum Game', (2011) undertaken by Katarina Gospic

https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001054


Behave (2017) by Robert Sapolsky is published by Vintage.


The Emotional Brain (1998) by Joseph LeDoux is published by Weidenfeld and Nicolson.


Synaptic Self: How Are Brains Become Who We Are (2002) by Joseph LeDoux is published by Penguin.

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