11 Aug Emotion – The Perturbable Mr. Amygdala
Have you ever been asked not to be so emotional, or on the contrary, to show more emotion? Or have you been asked to suppress a specific emotion, such as fear? I recall a scene from an Indiana Jones movie in which, after a scene of amazing heroics, a pilot tells Dr. Jones to suppress his fear of snakes saying “Show a little backbone, will ya.” Fear, and the resulting adrenalin surge, may be a great asset to a person in a pinch. The amygdala is where this asset is managed (Science Daily Article).
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The amygdala is another name for the amigdaloid nuclear complex located just in front of the hippocampus. The amygdala has direct connections with interpretive and emotive centers throughout the brain. This permits the amygdala to serve as an interface between our perceptions, our thoughts, and the physical manifestations of our emotions. By sending impulses to the hypothalamus, the amygdala regulates emotional and aggressive behavior. Release of hormones such as estrogen and growth hormone are directly influenced by amygdaloid nuclei. These hormone releases affect our physiology. The feedback they provide can affect our attitude or emotions.
Besides hormone balance, the amygdala has an impact on our respiratory rate, rhythm and amplitude, blood pressure, and secretion of digestive juices. In short, the amygdala affects all the major systems of the body except, possibly, the skeletal system.
|Roles of the Amygdala
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This table (See Pansky, et al., 1988) shows some of the ways the amygdala affects physical expressions of emotion through the hypothalamus. The amygdala is where emotions find expression. The amygdala affects aggressive behavior, ovulation, fear, amnesia, rage, respiration, heart rate, blood pressure, and ulcers.
If we follow pathways between the input and output fibers of neurons, we can discover how different areas of the brain are wired together. This can be done physically, through microscopy, which can identify the physical paths. It can also be done electronically, through imaging, which finds the functional paths (the actual flow of impulses). The illustration at right shows typical input and output pathways for the Hippocampus.
Caution is a reflex triggered by emotional responses to fear or other apprehension. This reflexive response arises out of specific triggered impulses launched in the amygdala and sent to four different parts of the brain:
- the central gray matter to stimulate a sudden cessation of dangerous activity or the reflex to freeze;
- the lateral hypothalamus to raise the blood pressure and prepare the body for rapid response;
- the paraventricular hypothalamus to release stress hormones;
- the reticulopontis caudalis to trigger the startle reflex.
[LeDoux, 1996, p. 160]
The large illustration nearer the top of this post depicts the flow of these impulses. In other posts, we will look more closely at the roles of emotions in cognition and consciousness.
Pathways of Stress
The amygadaloid nucleus is the originating point for responses to DANGER as shown in the illustration at right. The regulation of chemicals, including stress hormones such as steroid hormone and adrenalin, is a key link between cognition and behavior. It is interesting to note that the stress mechanism can get stressed out. After repeated or prolonged stress exposure, the cognitive and learning abilities of lab animals have been shown to diminish profoundly. No wonder Dr. Jones had trouble with Jock’s pet snake!
Memory is also linked to the cognitive mapping function of the hippocampus, so overburdening that organ with stress can be linked to decreased retention. In other posts, I discuss the possibility of a dichotomy existing between the “mind” and the brain. We’ll also explore the possibility that the functions of the hippocampal and amygdaloid formations indicate that other body systems indirectly participate in cognition.
Can we, and should we model the amygdala in intelligent automata? Will joy, fear or loneliness ever serve a machine as well as they may serve humans? We’ll do what we can to tie all these ideas together as we seek a model for more intelligent devices.
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