Instructor Notes — Chapter 21

Estimated class time: two sessions of 75–90 minutes, or one long seminar. If you only have one session, teach §21.2, §21.5, and §21.6 and assign the rest.

Prerequisites that actually matter: Chapter 2 §2.2 (concentration-dependent selectivity) and Chapter 5 (the rating rules). Chapter 3 helps but the chapter re-explains what it needs. Chapter 20 supplies orientation only.

What this chapter is for

Structurally this is a neuropeptide chapter. Pedagogically it is a science-communication chapter wearing a neuropeptide costume, and if you teach it as a survey of oxytocin physiology you will have taught the least valuable third of it.

The chapter's real subject is how a field-wide error gets built out of components that are each individually reasonable: a good animal finding, a cheap human paradigm, a story shape that compresses well, and a delivery assumption nobody validated. Students who leave able to recite that oxytocin is not the love hormone have learned the conclusion. Students who leave able to reconstruct how a room full of competent people arrived at the wrong place have learned the chapter.

The three things students most often get wrong

1. They flip from credulous to cynical in one step. This is the dominant failure mode and it will happen in your room. A student who arrives believing "oxytocin makes people trusting" will, by the end of §21.6, be saying "oxytocin is fake" and "the studies were all garbage." Both are the same error: accepting a confident summary in place of a state of evidence. Have the ✅ obstetric rating ready to deploy the moment this starts. Oxytocin is on the WHO Essential Medicines List. It is not fake.

2. They read the vole work as bad science. It is not, and the chapter says so three times. If your class comes away thinking the vole researchers overreached, they have missed that the overreach happened downstream, in reporting, mostly not by the original authors. Case study 1 exists specifically to protect this distinction; assign it if the class is drifting.

3. They convert the delivery controversy into a debunking. "It doesn't even reach the brain" is not what the chapter says and is not what the evidence supports. The honest statement is that it has not been established. Students find unresolved states genuinely uncomfortable and will resolve them without noticing. Watch for the tense shift from "has not been shown" to "has been shown not to."

Sequencing advice

Teach §21.2 before §21.4 and §21.5, even though it is the boring one. The chapter is deliberately ordered so that the ✅ is established before any skepticism starts, and reordering breaks the safety rail described above. If you are compressing, cut §21.8 rather than §21.2 — Chapter 29 owns desmopressin anyway.

§21.6 is the most transferable section in the chapter and the one students will use most in later parts. Budget accordingly. If you have time for one deep dive, make it this one and pair it with case study 2.

Handling §21.7 (autism)

Read the chapter's framing before class and be prepared to hold it. The chapter states, before any result is reported, that autism is a form of neurodivergence rather than a disease to be cured, that many autistic people object to "treatment" framing, and that outcome measures scoring conformity to non-autistic norms encode an undefended value judgment.

Practical notes:

• Assume autistic students are present. They may or may not be out. Teach the section as though the people it is about are in the room, because they probably are.
• The framing is not a disclaimer to be got past. It has methodological teeth: it changes what a primary outcome measure is measuring, which is the point exercise E6 tests.
• Do not let the room settle into "so the drug failed, which is good." That is a different value judgment, equally undefended. The honest position is that a well-conducted trial of a plausible hypothesis returned a negative result, and separately that the endpoint choice deserved scrutiny it did not get.
• If a student wants to argue the neurodiversity position is wrong, let them, and hold them to the same evidentiary standard the chapter holds everyone to. The bib file lists autistic-authored sources as a required citation category; point students there rather than adjudicating in the room.

Board work that lands

The sign-flip demonstration. Draw the affiliation model on the left: oxytocin → affiliation → trust up. Draw the salience model on the right: oxytocin → gain on social cues → branches to in-group and out-group. Then ask the class to place "increased out-group defensiveness" on the left-hand diagram. They cannot, and the reason is that the left diagram has no term for context. This is the single most effective five minutes in the chapter and it makes the abstract point about missing variables concrete.

The ambiguity square. Two-by-two: result (null / positive) against explanation (biology / delivery). Fill it in with the class. The realization that arrives — that all four cells are live and the studies were not designed to distinguish them — is what makes §21.6 stick.

Assessment notes

• exercises.md has 34 items across sections A–F; 11 are marked †. Sections A and B are safe for homework; C through F reward discussion.
• quiz.md has 22 items with a collapsed key. Items 5, 13, 17, 20, and 22 are the discriminating ones.
• Marking guidance and full answers are in _scratch/answers/ch21.md. The standing rule there is worth announcing to students in advance: any answer containing invented effect sizes, p-values, or sample sizes fails the item. The chapter supplies no numbers, deliberately, and students who produce them have either fabricated or imported them.