In the end these brain volume issues really apply only to small and quite specific areas. They really are visible evidence of different ways of processing information (which may be maladaptive). The real trouble is that because ADHD is defined by psychiatrists they take arather limited view of it- neglecting the physical signs which should by all irghts be identifiable in a neurological condition. Things are less backward in Europe though: A Swedish study: http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8749.2009.03407.x/full “Reliability and validity of the assessment of neurological soft-signs in children with and without attention-deficit–hyperactivity disorder” Additionally we are getting stronger and stronger evidence of problems like oculomotor problems – which are stimulant responsive: https://www.ncbi.nlm.nih.gov/m/pubmed/12672781/?i=4&from=/24691355/related Altered control of visual fixation and saccadic eye movements in attention-deficit hyperactivity disorder. Oculomotor Abnormalities in Children with Attention-Deficit/Hyperactivity Disorder Are Improved by Methylphenidate. Bucci MP, et al. J Child Adolesc Psychopharmacol. 2017. https://www.ncbi.nlm.nih.gov/m/pubmed/28452866/?i=1&from=dopamine%2C+fatigue%2C+oculomotor%2C+exercise Which is: Effects of Dopamine and Norepinephrine on Exercise-induced Oculomotor Fatigue. So lets think about this- attending with the eyes (reading) is a major part of the disability in ADHD, it is correlated with ocuomotor deficiencies that are improved with stimulants The same set of problems can be demonstrated in athletes who are exercised past their fatiguing point. So we have a plausible mechanism for oculomotor symptoms as a cause of ADHD symptoms, we know that they are ameliorated by stimulants. We also know that at least in the earl stages of treatment they substantially improve attention and learning (until you learn too much, read too much and exacerbate the problem. If we take this a little further we see that behavioural optometrists use a questionnaire that asks many questions that overlap with ADHD questions. Now these oculomotor problems are treatable by behavioural optometrists and by people who specialise in neurological rehabilitation/ functional neurology, most of whom are highly trained chiropractors. I have discussed the issue with one of them (when I was seeing him for treatment for my ADHD/Oculomotor issues [now almost full settled]) and he agreed with my reasoning that given the serious oculomotor fatigue and problems with training in bad habits during neuro-rehabilitation, the use ofsimulants then may be indicated. That’s pleasing really- hitting relevant mechanisms, and aiming to minimise duration of treatment. however, I do not think there is any sense in denying the problem exists, and zi think there is no sense at all in labelling a condition as a neurobehavioural condition without doing a proper physical examination. This approach is rare in psychiatry though.