Catani et al. (2012), emphasize the importance of understanding how large-scale, distributed brain networks link various brain regions through white matter tracts [103]. They used diffusion tensor tractography to map a new atlas of white matter connections (which can be viewed at www.​natbrainlab.​com). This sophisticated model further expands upon Schmahmann et al.’s comprehensive descriptions of how lesions of association fibers compromise communication between cortical and subcortical structures and affect a wide range of behavioral domains [104]. Catani and colleagues reviewed the “classical” neurobehavioral syndromes associated with frontal, parietal, temporal, occipital, and limbic lesions. They reported cases with a wide range of pathologies such as CVA, vascular malformations, traumatic brain injury, leukoencephalopathies, infectious diseases, as well as certain neuropsychiatric disorders. They demonstrated that classic neurological behavioral symptoms can be generated by disruption within cortical-subcortical connecting pathways. They also demonstrated how complex syndromes can result from dysfunction within an extended network of cortical and subcortical regions connected by multiple tracts. This helps explain comorbidities and seemingly incongruent behavioral presentations [103].

These networks define the distributed nature of neuronal processing that can serve as points of reference in examining specific symptoms in practically all neuropsychiatric disorders, including ADHD. This viewpoint is consistent with what is known about the neuroanatomy of performance on traditional neuropsychological tests. Most procedures employed in neuropsychological evaluation involve networks of multiple brain regions, and the functional neuroanatomy that drives test performance typically changes as the task is learned (see Koziol and Budding (2009) [5], for review).

The frontoparietal network consists of the dorsolateral prefrontal cortex, the anterior cingulate cortex, the anterior prefrontal cortex, the lateral cerebellum, the anterior insula, the caudate nucleus, and the inferior parietal lobe. This network is commonly engaged during effortful cognitive tasks that require rules to be kept in mind to guide behavior. This can be construed as a cognitive control, executive function, working memory type of network. Many previous studies have demonstrated recruitment of frontoparietal regions, regions of the basal ganglia, and the cerebellum on working memory tasks [105–109]. This executive control network underpins goal-directed behavior, particularly in novel problem-solving situations. It guides decision making by integrating external information with internal representations or ideas, so behavior can flexibly respond to changing task demands. Different aspects of this network serve different functions; mental representations are robustly kept “online” within prefrontal-parietal circuits; basal ganglia operations allow for the manipulation and updating of these ideas; and the cerebellum appears to “copy” the content of cortical working memory to assist in adapting and automating new responses [110–112]. Aspects of this circuitry have been strongly implicated in ADHD and in motor inhibition [113–115].