David J. Linden - Vice, Virtue and the Brain's Pleasure Circuits


Dutch experiment on genitally induced orgasm while in the PET scan showed that areas of the brain that get deactivated include those for social cognition and reasoning.

People don't become addicted to LSD, mescaline, SSRI, or other compounds that don't activate the dopamine pleasure circuit. In short, if it activates the dopamine neurons, then there's a chance it's addictive, otherwise not.

Animals in the wild will also voluntarily consume psychedelic plants and fungi. Some animals in Africa (e.g. elephants) consume Iboga and goats eat coffee berries.

Due the animals really like them, or do they just put up with the side effects of a nutritious food source?

It looks like they like them: low nutritional value, high hallucinogenic value.

Reindeer eat hallucinogenic mushrooms such as Amanita muscaria and they also lick a leftover acid from urine in snow. The Chukchi population collect the urine and Siberian reindeer are just as attracted to human urine with the drug trace in it as to their own.

Humans can activate the pleasure circuit even in ways that do not help spread the genes in any way (not even through kin selection): fasting, abstaining from sex, celebrity gossip.

Gambling: it could be said that the pleasure center gets activated during the mere wait for the game to settle (e.g. the wheels spinning), not only if you win.

Anything that can activate the pleasure circuit can be a substrate for addiction.

Addictions run in families. One reason is genetic. To isolate this variable, we study monozygotic and dizygotic twins who were adopted. ("They are very few, but boy, do we study them"). Human BMI is 80% inheritable. 40% of the propensity for addiction can be explained genetically; the rest: the experience. The most important aspect of experience is stress, in any form: job loss, fight w/ someone, fighting off infection.

Only 35% of those who injected heroin became addicted. Marijuana is addictive in only 8% of users. With alcohol, the percentage is only 4%, but higher in poorer countries. Surprisingly, alcohol doesn't lead to violence in France, while it does so in England. There is no clear theory as to why. 80% of all people who tried cigarettes became addicted. Explanation: heroin acts for hours, so the heroin addict gets two strong hits per day, while the smoker gets 200 weak hits every day. Analogy with dog training: if you call the dog twice a day and reward with a 10lb steak, it will learn less effectively thank if you call it 200 times a day and reward with small treats.

Mice without the mGLUr5 receptor are utterly indifferent to the reinforcement effects of cocaine or other drugs. They don't appear to "get high" on cocaine, as they don't press the lever to get more of the addictive substance.

The only rational stance towards an addict is compassion; like what we'd feel towards someone with a heart disease. It's difficult to have this compassion, esp. towards sex addicts (because of the implicit immorality) because we have to admit our lack of complete free will.

A study by Lucy Brown at Albert Einstein College of Medicine. showed that looking at the picture of the sweetheart (vs. platonic friend) showed under fMRI down-regulation of the reason centers. When the study was repeated on people who had been married for 15 years, 5% were just as passionate, while the others said the feeling morphed into affection/loving but less passion. Those 95% did not have reduction in the reasoning and social cognition areas.

A cat's humorous perspective on humans' conventional sex:

  • pointless to mate during non-fertile period
  • limiting to one partner? ha.
  • all this privacy?
  • the dad hanging around to take care of the kids?

Examples of sexual "kink" in nature:

  • Female orangutans have made dildos
  • Bottlenose dolphins wrap an eel around their penis
  • Homosexual behavior has been documented in 500+ species
  • Only example of nasal sex: penis in blowing hole

Homosexual sex happens also outside reproduction period. Sex across species and necrophilia have also been observed.

It's not the kinky that makes humans sexually unique. What's totally aberrant is the social conventions associated with sex.


Q: Are we pleasure automatons, or are there techniques we can use to stay rational?
A: There is no rationality without pleasure. People who are unable to feel pleasure (anhedonic) are not hyper-rational, but the opposite. All cognition is emotional; all is driven, to some extent, by plain and pleasure.

Q: Are there generalized changes in the brains of addicts?
A: When you become addicted, the pleasure center is modified, so it's hard to take pleasure in anything else. Food addiction (90% of obesity is food addiction, only 10% is metabolic) is a special case - it lets the medial-frontal center of pleasure take pleasure in other things than food. The pleasure circuit gets blunted across a wide range of addictions.

People relapse during stressful situations. So if you get stress reduction out of walking your dog, exercise, or prayer, fine.

"Ibutrin" anti depressant also helps addicts. These drugs don't just blunt the pleasure system and leave you feeling indifferent to everything. Parkinson's disease is not just of movement, but of personality as well. Patients feel less and less pleasure.

Q: Is generosity addictive?
A: Study by Bill Harbaugh at University of Oregon: people were given money and the ability to give some of it to charity. We are intrinsically hardwired to take pleasure from social regard. But even if people are convince that nobody will know (when donations are made through software), pleasure is activated when giving.

Both pleasure and pain mark salience, things that are important: "This is an experience that you should attempt". Our brains perceive spicy food as extra salient.

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