ebook_ADHD2019_engl.

The World Federation of ADHD Guide 113 That said, it is always important to check that the threshold is set at the right point and that pressures from families, society or private interests like those from the pharmaceutical industry are not influencing the cut off point. Finally, the definition of ADHD is not only based on the severity of symptoms causing impairment but also on the pervasiveness of them in different settings of life. This approach will help to differentiate ADHD from conditions that are a reaction to specific triggers in the environment such as inattentiveness only in the classroom setting because of an inadequate teaching method. THERE ARE NO BRAIN ABNORMALITIES OR DYSFUNCTIONS IN ADHD Probably, the most cited argument against the validity of ADHD is that science has never found a brain abnormality that exists in all individuals affected by the disorder. This is a true assertion used in wrong way. Science will never find a single brain abnormality in all ADHD brains. This is why: ADHD is a syndrome, which means that individuals with the disor- der have different profiles of symptoms in one of the two dimensions that charac- terize the disorder, inattention and hyperactivity/impulsivity. In some populations, impulsivity and hyperactivity form different dimensions and we have three and not two dimensions. We call this phenomenon phenotypic heterogeneity meaning that, as not all humans are equal, not all patients with ADHD have the same symp- toms. Thus, we have some brain abnormalities that are probably related to a speci- fic group of symptoms in each of these dimensions. Whenever a group of patients with ADHD have a scan in a Magnetic Resonance Imaging (MRI), differences are detected in their brains compared to individuals without ADHD, but the same brain abnormality is not present in all brains due to the phenotypic heterogeneity. Figure 6.1 below, illustrates a picture of what information ADHD research pro- vides so far and what additional information is needed. Imagine that each point represents a specific characteristic of the brain of one individual (e.g., thickness of the pre-frontal cortex). In Figure 6.1A, you have where we are. When you cal- culate the mean of the thickness of the pre-frontal cortex of individuals in group 1 (ADHD), it is significantly lower than the one for group 2 (individuals without ADHD), but, as you can see, several individuals with ADHD (group 1) have the same thickness of the pre-frontal cortex than those of individuals without ADHD (group 2). They are probably different in other structural and/or functional brain characteristics compared to individuals without ADHD. The challenge is to have a composite measure including several structural and functional brain characteris- tics that can separate groups as in Figure 6.1B. With better scans, larger samples of patients and sophisticated new data analytic techniques as machine learning, we are getting closer!