Evidence suggests that it really affects what psychiatrists like me call sustained engagement — an important difference in understanding how to think about the condition. As a psychiatrist, I increasingly see people seeking help for a familiar constellation of troubles. They have a hard time staying focused. They often forget things. They suffer from disorganization, restlessness and impulsivity. They struggle with spreadsheets and memos, with laundry and food preparation, with showing up at appointments and meeting deadlines — with tackling, in other words, the necessities of daily life. Increasingly, these patients view their problems as ones of 'attention,' as more people identify with the diagnosis of attention deficit hyperactivity disorder, or A.D.H.D.

The rise in A.D.H.D. diagnoses — along with the use of prescribed stimulants like Ritalin or Adderall — has led to great debate among the public and within my field of psychiatry. Has the medical establishment finally recognized a long-overlooked disorder? Or has the diagnosis become too capacious, over-medicalizing ordinary difficulties? But this debate runs up against a fundamental scientific uncertainty. The condition's name notwithstanding, 'attention deficit' may be the wrong conceptual framing for A.D.H.D.

Scientists have been exploring a more basic quandary: What is the condition in the first place? A major study published last year in the journal Cell spoke directly to this question. It looked at how stimulant medications influence the functioning of brain circuits in children. The researchers found that the drugs seemed to affect brain networks involved in salience, reward and arousal. But they found no detectable changes in the brain's attention networks, whether or not the child had been diagnosed with A.D.H.D. It's a clear signal that the most popular mental model for A.D.H.D. — as a deficit of attention that stimulants remedy — might not be entirely accurate.

What would a better mental model look like? Part of the answer is understanding that 'attention' means different things in the clinic and in the neuroscience lab. For scientists studying brain functions, attention means something narrow: the selective amplification of relevant information. It can be measured by laboratory tasks that assess, for example, how well someone ignores irrelevant or conflicting information or finds a target hidden among distractions. But that's generally not what people mean when they are talking about attention problems in A.D.H.D. The classic features of A.D.H.D. include things like not staying on task, losing the thread of a conversation and forgetting instructions. They are failures of 'sustained engagement.' If attention is about the mind homing in on what's relevant in a given moment, engagement is about keeping that spotlight pointed at the same target over time.