ADD (or ADHD — note the vagueness of terminology) is only now beginning to be measured objectively:

Last fall the National Institutes of Health awarded Dr. Teicher a $1 million grant from the federal stimulus package to delve further into the quest for a definitive test or biomarker for the disorder. He plans to focus his research on three detective strategies: his Quotient system, magnetic resonance imaging to compare blood flows in different brain regions, and the ActiGraph, an activity monitor widely used by medical researchers.

James M. Swanson, a developmental psychologist and attention researcher at the University of California, Irvine, praised Dr. Teicher’s research, echoing his concerns about the need for a more objective test to detect the disorder. But he questioned whether the Quotient system produces more reliable diagnoses than a doctor’s dogged questioning of a child’s parents and teachers, and also whether it is an appropriate way to figure out the right dose of medication.

“It’s essentially a dull, boring task,” he said of the Quotient system, “so do you want to medicate your child to pay attention to dull, boring tasks?”

The key to his system, he said, is what he suspects will eventually be confirmed as a valid biological marker for A.D.H.D.: an unstable control of head movements and posture, particularly while paying attention to a boring task.

Decades ago modern medicine all but stamped out the nervous breakdown, hitting it with a combination of new diagnoses, new psychiatric drugs and a strong dose of professional scorn. The phrase was overused and near meaningless, a self-serving term from an era unwilling to talk about mental distress openly.

But like a stubborn virus, the phrase has mutated.

In recent years, psychiatrists in Europe have been diagnosing what they call “burnout syndrome,” the signs of which include “vital exhaustion.” A paper published last year defined three types: “frenetic,” “underchallenged,” and “worn out” (“exasperated” and “bitter” did not make the cut).

This is the latest umbrella term for the kind of emotional collapses that have plagued humanity for ages, stemming at times from severe mental difficulties and more often from mild ones. There have been plenty of others. In the early decades of the 20th century, many people simply referred to a crackup, including “The Crack-Up,” F. Scott Fitzgerald’s 1936 collection of essays describing his own. And before that there was neurasthenia, a widely diagnosed and undefined nerve affliction causing just about any symptom people cared to add.

Yet medical historians say that, for versatility and descriptive power, it may be hard to improve upon the “nervous breakdown.” Coined around 1900, the phrase peaked in usage during the middle of the 20th century and echoes still.... Never a proper psychiatric diagnosis, the phrase always struck most doctors as inexact, pseudoscientific and often misleading. But those were precisely the qualities that gave it such a lasting place in the popular culture, some scholars say. “It had just enough medical sanction to be useful, but did not depend on medical sanction to be used,” said Peter N. Stearns, a historian at George Mason University near Washington, D.C. ...

The vagueness of the phrase made it impossible to survey the prevalence of any specific mental problem: It could mean anything from depression to mania or drunkenness; it might be the cause of a bitter divorce or the result of a split. And glossing over those details left people who suffered from what are now well-known afflictions, like postpartum depression, entirely in the dark, wondering if they were alone in their misery.

But that same imprecision allowed the speaker, not medical professionals, to control its meaning. People might be on the verge of, or close to, a nervous breakdown; and it was common enough to have had “something like” a nervous breakdown, or a mild one. The phrase allowed a person to disclose as much, or as little, detail about a “crackup” as he or she saw fit. Vagueness preserves privacy....

“People accepted the notion of nervous breakdown often because it was construed as a category that could handled without professional help,” concluded a 2000 analysis by Dr. Stearns, Megan Barke and Rebecca Fribush. The popularity of the phrase, they wrote, revealed “a longstanding need to keep some distance from purely professional diagnoses and treatments.”

Many did just that, and returned to work and family. Others did not. They needed a more specific diagnosis, and targeted treatment. By the 1970s, more psychiatric drugs were available, and doctors directly attacked the idea that people could effectively manage breakdowns on their own.

Psychiatrists proceeded to slice problems like depression and anxiety into dozens of categories, and public perceptions shifted, too.