Aggression - part 2.


As it was already mentioned before, when one has amygdala damage, they look less into the eyes. In other words, amygdala also “looks” for signals. Testosterone makes amygdala better at detecting fear and anger in faces. There is shortcut for visual information to amygdala (lateral geniculate). This is faster. E.g. cortex can still be deciding whether it is a 2D or 3D object, but one has already stubbed other person due to the shortcut (i.e. you trade speed with analytical accuracy). This pathway is hyper excitable in individuals with post- traumatic stress disorder.

Williams syndrome - imprinted genetic disorder. Kids having this disorder are facile with language and emotions, but cognitively impaired (IQ approximately 70). They are extremely trustful and, as a result, vulnerable. They can’t evoke amygdala activation through scary faces.

Social phobias - any face activates amygdala (i.e. any face is scary). Under clinical depression, amygdala activates when one observes something sad, in other words amygdala is contextual (sad is scary, when you have a depression).

Amygdala is also best at dichotomizing - us vs. them and responding to out-group stimuli. This will be considered in more details later.

Frontal cortex

Responsible for appropriate behavior. When there is a choice between doing something easy or hard (but better), frontal cortex makes us to do the harder thing. It does not apply strong influence, instead it has many weak and diffused projections. In other words, it gives bias via slowly “massaging” the signal. This works like modulation. In other words frontal projections are very diffused and relatively weak, so they bias towards excitation rather than cause it. Frontal cortex also has inhibitory projections.

Dopamine is “fuel” for this activity. It is not only about anticipation, but also about driving the behavior needed.

Frontal cortex also handles gratification postponement.

Frontal cortex neurons have high metabolic rates (i.e. work hard), but are also very fragile, which leads to many frontal cortex disorders.

California Verbal Learning Test

There is a test for dementia - CVLT - California Verbal Learning Test. A tester tells one: “Today I bought [list of 16 unrelated items]” and then asks to repeat the items. However, items can be separate into 4 categories, e.g. 4 fruits, 4 hardware etc. The tester repeats the sentence and one can remember more and more each time. However, one also begins to group items into categories. E.g. they remember fruits first and name them and so on. This is executive function - notice patterns, try to keep track of categories. Frontal cortex handles this. When there is frontal cortex damage, one remembers items as usual, but never does the grouping. In other words, frontal cortex does “I see a pattern, I suspect if I put effort to exploit it, this will make me more productive”.

There is also another test. One sees a circle and then is given time of the day like “11:10”. They are asked to draw the time as if the circle is a clock. One draws hours at 11 and then minutes at number 10, because this is the easiest interpretation.

Another test is to name months backwards. One starts with December, then November, October, September and then switches to go forward again, i.e. October, November. They can’t hold off overlearned, more habitual response.

When then they are asked to count from 20 to 1, they do 20, 19, 18, 17, September, October, i.e. slip into the previous task (it intrudes the next one).

Learning rules

Imagine there is a monkey. They need to pull a lever after seeing a visual light signal to get food. You see visual system activity increase during each signal. Frontal cortex gets activated after the first signal and stays activated - tries to learn the rule from individual examples.

At some point some rule becomes automatic, i.e. it gets stored somewhere else in the brain. E.g. a demented person may be not able to tell names of their children, but be able to knit (since they learned that as a kid). Cerebellum seems to play large role in this.

Social behavior

Same applies to social behavior, e.g. Phineas Cage [wiki] - foreman at a railroad construction in 1840s. There was an explosion and a metal rod went through Cage’s head damaging frontal cortex. It was hot due to explosion, so it cauterized the blood vessels. Cage was conscious shortly after the impact. Before the event, he was sober, religious and highly reliable. After - abusive, sexually predatory, out of control.

Nowadays one can study frontal cortex via older people with natural damage.

25% of men on death row had a history of concussive head trauma to the front of the head.

There is Mc Naughton rule in the US - if individual can’t tell difference between right and wrong, they are considered organically impaired (i.e. this is insanity defense rule). Not seeing a difference between right and wrong implies e.g. not covering tracks after a criminal act.

E.g. John Hinckley (severe schizophrenic) tried to assassinate Reagan in 1981. He was found not guilty by reason of insanity. However then Mc Naughton rule got implicitly banned, since people were unhappy that Hinckley was “getting away”.

However, there are people with frontal cortex damage, who can tell the difference between right and wrong, but can’t control themselves. One can suggest such a person 5 candies in one hand and 1 in other. When the person chooses 5, they get the other hand, i.e. 1. They always choose 5 and get 1. They can even explain you the rule and then choose 5 anyway.

Chimps fail this test too, but they pass when you give them wooden pieces to choose from (but reward with candies). I.e. they can control themselves enough when it is about wood (they don’t care much about it).

For kids there is one classic developmental test with marshmallow. One gets left in a room with a marshmallow. If they don’t eat it, they will get 2 instead. This test predicts frontal cortex metabolism as well as SAT scores many years later.

Little kids have not developed frontal cortex. As a result, when you play hide and seek with them and ask “where are you?”, they reply because they can’t stop themselves. Also when they count, they do 7,8, 9, 14, 17 - they can’t inhibit. At age 5 there is a relation between resting frontal cortex metabolism and socioeconomic status. Glucocorticoids atrophy neurons here (they have the most receptors here). I.e. stress of poverty affects size and activity of frontal cortex.

There was another example of a mass murdered, who had a massive car accident when he was 6 years old, which destroyed his frontal cortex. As a result, in 11 years he committed the first murder. The last crime was kidnapping a women. After holding her for a week, he just casually brought her home and left his phone number suggesting to meet again, since he had a great time with her. He got arrested in an hour.

“Acquired sociopathy” - one get’s only some part of rules, especially when getting frontal cortex damage before 5-6 years of age.

However, not all frontal cortex damage makes a person murderer. They just can be out of control. E.g. one can be playing piano at a social gathering for too long, not listening to anyone.

In 18th century epilepsy was considered a demonic possession. The person was considered a witch and burned. The legal test was - if they don’t cry due to a story of crucifixion, they must be a witch. Then there was a person noting that glands can atrophy, i.e. a person can be organically impaired and won’t be able to cry at all. Does the same apply to frontal cortex damage? What should the court do?


Frontal cortex is the last part of the brain to fully develop. On average it matures around the age of 25. As a result, it is the least constrained by genes (instead shaped by environment and experience).

In teenagers - dopamine variation is much stronger (i.e. when adult has low dopamine, teenager has even lower and otherwise). As a result there is no death penalty for crimes made between 16 and 18 years, since the brain is not fully mature yet. However, it is not clear what exactly happens to one’s brain on their 18th birthday, making death penalty ok.

This is third most vulnerable region to normal aging.

  1. Substantia nigra - motor system (thus, tremor of old age Parkinson’s)

  2. Hippocampus - memory problems

Often people believe that older people accept how they are and listen less to opinion of others because of that, but this is due to frontal cortex damage.

Resting metabolism variations

People with elevated frontal cortex metabolism. Highly regimented, disciplined, capable of controlling their behavior. Do not express emotions very readily, bad at reading emotions in other people. They have extremely structured life. This is due to elevated resting metabolism in frontal cortex.

Thrill seekers and sociopaths e.g. have lower levels. For them it takes more work to regulate (i.e. more frontal cortex gets involved).

Relation to amygdala

Amygdala can regulate frontal cortex (both have inhibitory projections). There is inverse correlation in activity. Without frontal cortex amygdala can’t learn to stop being afraid. They can work together e.g. when a harder behavior is scary (e.g. running towards the enemy in a war).

Other parts

Septum - inhibits aggression.

Lateral hypothalamus - predatory behavior (food acquisition).

Anterior cingulate - empathy (feeling pain of others).

Josh Green did the following test. Imagine you are a group of people hiding from enemy in a war and you have a crying baby in the group. Do you kill the baby? People who activate anterior cingulate less are more likely to do so.

Josh Green also did runaway trolley problem. You choose between “not doing anything - 5 people die” and “pull a lever or push a person with your hands - 1 person dies”. 75% are willing to pull the lever. Only 25% are willing to push.

There is transmagnetic stimulation which allows to turn parts of frontal cortex on, this leads to more utilitarian and more selfish decision making.

Abstract concepts

We have a lot of metaphors in our life, e.g. reputation, plagiarism. However, we treat abstract concepts like real. E.g. the following study. One in an elevator. Another person comes with a drink in a cup and a bunch of books and asks the first person to hold the cup. There may be a warm or a cold drink there. Afterwards the first person rates the personality of the second person warmer if the drink was warm. I.e. we intermix warmth metaphor with actual temperature. In other words, metaphor storage is based on hijacked pathways for storing temperature.

When you see something disgusting (e.g. rotted food), insular cortex activates. When you hear a story of someone powerful mistreating someone else (in a really exploitative rotten manner), the same area also activates. In other words, it handles cases of food being bad, moral & self disgust.

This even can be seen in the language, e.g. “I am disgusted by what you did”. Also “nauseous”, “smells rotten” - i.e. terms intermix sensory disgust with moral disgust. I.e. moral disgust is shoehorned in this part of the brain.

People thinking of their moral failings are more likely to choose soap as a reward afterwards to “wash their hands of their sins” (study).

If one is allowed to wash their hands of their metaphorical sins, they are less likely to help the other person who dropped books (study).

That’s how mammalian brain does abstract thinking.

Jonathan Haidt did the following study. Ask people about

  • siblings having non-reproductive sexual relationship in private.

  • grandma asks to slap her

  • burn flag and step on it

  • eat your dead pet (when you are extremely hungry)

All of these activate insular cortex, people can’t explain what’s wrong. I.e. cognitive decisions catch up afterwards.

There are areas which activate in various contexts, e.g. for murder or orgasm it can be increases heart rate (i.e. non-specificity of arousal).

Elli Wiesel said that opposite of love is not hate, but indifference. Love and hate are physiologically similar.


Testosterone (like in sexual behavior) is required for expressions of aggression. The more prior experience one has, the more residual behavior they have when testosterone is removed. Behavior drives testosterone.

E.g. take a rhesus monkey. They build dominance hierarchy. Pump rank 3 out of 5 with testosterone. They start beating 4 and 5 more. I.e. testosterone only exaggerates existing social structure.

When testosterone is higher, amygdala threshold for a threatening face is lower.

Testosterone shortens refractory period of single neurons in amygdala. I.e. it does not cause anything, it only amplifies.


In spotted hyenas - females dominate males. They are bigger, more muscular, more aggressive, have more testosterone, androgenization. Clitoris has size of male penises. They are hormonally more male than males are.

Most lions starve to death in the first year of life, because the order to eat is males, females, cubs. In hyenas it is cubs, females, males.

In primates, when one tries to dominate they get an erection. In hyenas males get erections when they are terrified (this is subordinate gesture). Low ranking females also get clitoral erections.

The lecturer told a story about his friend getting invited to a conference on predatory behavior organized by the military. The explanation was that they wanted to teach tank corps to hunt like carnivores (in a good tank). The exact reason is not known.