Thread by @ed_hagen

The "neurotransmitters are drugs" metaphor, which is also applied to "surging" hormones in teenagers and women, has things exactly backwards.

🧵 1/n

https://twitter.com/WSJ/status/1429662192702480387

Your body has about 30 trillion cells, of which about 80 billion are neurons in your brain. All these cells constantly communicate with one another to create the organism that is you.

2/n

Cells communicate using chemical signals. Neurotransmitters like dopamine, serotonin, & acetylcholine are one class of chemical signals used by neurons. Testosterone, estrogen, & cortisol are another class of "hormone" signals. There are many others.

3/n

en.wikipedia.org/wiki/Cell_sign…

These chemical signals are being sent *constantly*. As you read this, every cell in your body is sending and receiving chemical signals. If dopamine wasn't constantly released & detected, your body would Not. Work. At. All. The same goes for many other cellular signals.

4/n

These chemical signals are ancient, and many of the same ones coordinate cellular activity in broad groups of animals.

5/n

We and all other animals get our food from plants, which is beneficial to us and (usually) harmful to the plant. (Consumption of fruits, which plants evolved to disperse their seeds, is beneficial to both plants and animals.)

6/n

Plants are sessile. To defend themselves from animals, they have evolved many defenses. Toxins are a key plant defense. Many toxins work by interfering with cellular signaling in animals.

7/n

Most popular recreational drugs, including nicotine, cocaine, and opium, are plant defensive toxins or their close chemical relatives (alcohol is the exception).

8/n

Cocaine defends coca plants by *interfering* with dopamine or octopamine signaling. Nicotine defends tobacco plants by *interfering* with acetylcholine signaling. Morphine and other opioids defend opium poppies by *interfering* with opioid signaling.

9/n

Plant toxins interfere w/ cellular signaling in herbivores by evolving to chemically resemble some step in their signaling pathways.

It is *not* that neurotransmitters & hormones are like drugs. Instead, drugs (i.e., plant toxins) are like neurotransmitters & hormones.

10/n

Drug-induced buzzes & highs are caused by the toxin's interference w/ essential cellular signaling.

So why are the routine & necessary signaling functions of dopamine, testosterone & other cellular signals so often equated w/ the disruptive effects of plant toxins (drugs)?

11/n

Because plant drugs interfere with neural signaling, and thus decision-making and behavior, there is a sense in which individuals are not "responsible" for their decisions and behaviors when these are influenced by plant toxins.

12/n

The "neurotransmitters & hormones are drugs" metaphor is often invoked when there are social conflicts. Teenage sexuality causes conflicts & is blamed on "surging hormones". Depression causes conflicts, & in the WSJ article is blamed on "brains getting hooked on dopamine"

13/n

Resolving conflicts will inconvenience someone. The "cellular signals are drugs" metaphor is so widely popular, IMO, because it provides a way to avoid resolving conflicts/or and avoid punishment.

14/n

Her teenage son knocked up (or sexually harassed) his teenage daughter? Teen hormones! His poor family environment is making him depressed and seeking escape in video games? His brain is hooked on dopamine!

15/n

The "cellular signals are drugs" metaphor is too useful to too many people to hope that it will disappear in popular discourse.

But scientists should know better.

end/

PS: Our papers on our evolutionary approach to drug use are here:

anthro.vancouver.wsu.edu/people/hagen/p…