ADHD in particular is located to very specific areas in the brain. Primarily the dorsolateral prefrontal cortex and areas in the cingulate cortex. We can see neuroanatomy differences on scans, which, while not specific or sensitive enough for diagnosis, are definitely real physical changes in the brain, and they're pretty consistent across diagnosed vs baseline.
There are lots of psychiatric disorders where that doesn't take place, but developmental neuropsychiatric disorders don't fall under that "are they even alike at all" kind of umbrella. In some kind of awful alternate universe we could pretty reliably induce them with gamma knife surgery, for example.
Depression is much easier to argue that it's a less specific symptom of a larger constellation, with lots of causes and lots of manifestations.
There are lots of psychiatric disorders where that doesn't take place, but developmental neuropsychiatric disorders don't fall under that "are they even alike at all" kind of umbrella. In some kind of awful alternate universe we could pretty reliably induce them with gamma knife surgery, for example.
Depression is much easier to argue that it's a less specific symptom of a larger constellation, with lots of causes and lots of manifestations.