[Attention deficit hyperactivity disorder: in favour of the organic origin]

To review the neurobiological findings that evidence the organicity of attention deficit hyperactivity disorder (ADHD).

The manifest inheritability favours the idea of a genetic base for the disorder. Functional neuroimaging techniques enable us to observe how the brains of ADHD patients function in real time. The most relevant work carried out in the field of neuroanatomy shows that the brains of children with ADHD are smaller and the same is also true of the cerebellum. On analysing more advanced techniques like magnetoencephalography, neurophysiological and functional studies have also revealed the existence of differences compared to healthy subjects.

Genetic tests have made it possible to focus research towards specific neurotransmitter systems, although the results are far from conclusive. Children with ADHD present alterations in their brain anatomy and neurophysiology, and magnetoencephalography studies have revealed an alteration in very early phases of information processing (before 200 ms). They have an early immature response in the left inferior parietal lobe, as well as in the posterior-superior temporal gyrus, and there is hardly any reaction in the anterior cingulate cortex. This implies that, although they perceive the stimulus and even display a stronger reaction to it, they do not process it as an interactive signal in the sector of the cingulate cortex. These data support the neurobiological bases of ADHD and, together with others, will allow for the production of endophenotypical classifications based on biological and, in the longer term, genetic evidence.