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The Amygdala

The amygdala is an almond-shaped structure located deep in the brain, in the medial (toward the middle) areas of the temporal lobes. Abundant evidence implicates the amygdala in a system for activating the cerebral cortex in the presence of external threats.

What is the main function of the amygdala?

Stimulation near the amygdala produces fear, anxiety, defensive, and sometimes violent behavior. King (1961) implanted electrodes in a schizophrenic woman, "in an attempt at therapy." The woman was interviewed and her amygdala was stimulated at intervals without informing her.

Subject : "I just feel like everything is all wrong. Like I can't be a part of anything. Like I didn't belong and everything is a dream or something."

Interviewer : "Did you feel this way before the operation (He is referring to the implanting of electrodes.)

Subject : "Yeah, I felt the same way. I didn't want anything and I didn't belong any more."

The subject's voice tone was extremely flat and lacking in emphasis. The region of the amygdala was then stimulated with a 5 milliampere current.

What was the effect of stimulating the amygdala in the schizophrenic woman?

Interviewer : "How do you feel now?"

Subject (voice much higher in tone): " I felt like I want to get up from this chair! Please don't let me do it!...Don't do this to me. I don't want to be mean!"

Interviewer : "Feel like you want to hit me?"

Subject : "Yeah, I just want to hit something. (Appears and sounds aroused and angry.) I just want to get something and tear it up. Take it so I won't!

(She hands her scarf to interviewer; he hands her a stack of paper, and without further verbal exchange she tears it to shreds.) I don't like to feel like this!

The level of stimulating current was then reduced to 4 milliamperes.

Subject : (immediately changing to a wide smile): I know it's silly, what I'm doing.

Interviewer : "Can you tell me anything more about how you were feeling a moment ago?"

Subject : "I wanted to get up from this chair and run. I wanted to hit something; tear up something, anything. Not you, just anything. I just wanted to get up and tear. I had no control of myself." (p.47)

Was it ethical to do this research? It seems like an experiment without much treatment value, and it probably would not be permitted today.

The researchers claimed they were looking for insights that might aid treatment of schizo­phrenia. However, it is not clear if they found out anything that helped the woman.

Activation of the amygdalar complex (the region around the amygdala) sometimes causes violent behavior. Might abnormal brain activity in this area account for some acts of random violence?

Charles Whitman, who climbed to the top of a tower on a Texas campus in full military gear and shot many students before being killed himself, was found on autopsy to have abnormalities near the amygdala. He also left a diary complaining of strange, irresistible impulses to violence.

Doctors Vernon Mark and Frank Ervin carried out a study with an epileptic girl, Julia, who had fits of violent behavior. They borrowed a radio-controlled brain-stimulating device from Jose Delgado and implanted electrodes in Julia.

Mark and Ervin stimulated Julia's brain in the region of the amygdala without warning her, as she moved around the hospital ward. During one such stimulation she was playing a guitar.

When Mark and Ervin activated the electrode in her amygdala, she suddenly smashed the guitar against the wall (Mark and Ervin, 1970).

What did Mark and Ervin observe when they stimulated a girls' amygdala?

The researchers justified this experiment on the grounds that they might obtain knowledge about the girl's condition that would help in her treatment. However, again, there is no evidence that it helped her, and again, it is unlikely a research oversight committee would approve such a procedure today.

Function of the Amygdala

The main function of the amygdala appears to be alerting the brain to external threats. In both the cases above, violent behaviors were the result of activating an alarm system. The result was to respond as if to a threat.

When the amygdala is removed from laboratory animals, they show no fear. A rat with its amygdala removed "will walk up to a sleeping cat and even nibble on its ear" (Barinaga, 1992). The amygdala is connected by large neural pathways to areas of the brain responsible for defensive behaviors.

When the amygdala is damaged in humans, they lose their fear of dangerous situations. A patient known as S.M. had amygdalar damage on both sides of the brain, and she felt no fear. When visiting an exotic pet shop, she wanted to touch the snakes and a tarantula (Feinstein, Adolphs, Damasio, and Tranel, 2011).

How might the amygdala be involved in shyness?

When the amygdala is overactive, it may produce oversensitivity to emotional arousal. Kagan and Snidman (1991) suggested that the amygdala might be involved in shyness. Stimuli other children interpret as neutral are perceived instead as a threat.

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References:

Barinaga, M. (1992). How scary things get that way. Science, 258, 887-888.

Feinstein, J. S., Adolphs, R., Damasio, A., & Tranel, D. (2011) The Human Amygdala and the Induction and Experience of Fear. Current Biology, 21, 34-38. doi:http://dx.doi.org/10.1016/j.cub.2010.11.042.

Kagan, J., & Snidman, N. (1991). Temperamental factors in human development. American Psychologist, 46, 856-862.

King, H. E. (1961) Responses to subcortical electrical brain stimulation in humans. In D.E. Sheer, (Ed.), Electrical stimulation oj the brain. Austin: University of Texas Press.

Mark, V. H. & Ervin, F. R. (1970) Violence and the Brain. New York: Harper & Row.


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