New Delhi, May 1 -- The diagnosis of attention-deficit/hyperactivity disorder has long been treated as a blunt instrument, symptoms first, biology second. That model is now under direct assault.

the disorder is not one condition, but several, each wired differently in the brain.

At the center of the upheaval is a newly characterized subtype that is not merely more severe, but fundamentally different.

A Disorder Misunderstood

For decades, ADHD diagnosis has relied on observable behavior: inattentiveness, hyperactivity, impulsivity. It is a system rooted in checklists, not circuitry. But the latest research discards that framework and starts instead with the brain itself.

By analyzing structural and neurochemical patterns, researchers ...