Adult ADHD has been linked to impaired motor response inhibition and reduced associated activation in the right inferior frontal cortex (IFC). However, it is unclear whether abnormal inferior frontal activation in adult ADHD is specifically related to a response inhibition deficit or reflects a more general deficit in attentional processing. Using functional magnetic resonance imaging, we tested a group of 19 ADHD patients with no comorbidities and a group of 19 healthy control volunteers on a modified go/no-go task that has been shown previously to distinguish between cortical responses related to response inhibition and attentional shifting. Relative to the healthy controls, ADHD patients showed increased commission errors and reduced activation in inferior frontal cortex during response inhibition. Crucially, this reduced activation was observed when controlling for attentional processing, suggesting that hypoactivation in right IFC in ADHD is specifically related to impaired response inhibition. The results are consistent with the notion of a selective neurocognitive deficit in response inhibition in adult ADHD associated with abnormal functional activation in the prefrontal cortex, whilst ruling out likely group differences in attentional orienting, arousal and motivation. Hum Brain Mapp 35:5141–5152, 2014.

Attention deficit hyperactivity disorder (ADHD) persists frequently into adulthood. The decomposition of endophenotypes by means of experimental neuro-cognitive assessment has the potential to improve diagnostic assessment, evaluation of treatment response, and disentanglement of genetic and environmental influences. We assessed four parameters of attentional capacity and selectivity derived from simple psychophysical tasks (verbal report of briefly presented letter displays) and based on a "theory of visual attention." These parameters are mathematically independent, quantitative measures, and previous studies have shown that they are highly sensitive for subtle attention deficits. Potential reductions of attentional capacity, that is, of perceptual processing speed and working memory storage capacity, were assessed with a whole report paradigm. Furthermore, possible pathologies of attentional selectivity, that is, selection of task-relevant information and bias in the spatial distribution of attention, were measured with a partial report paradigm. A group of 30 unmedicated adult ADHD patients and a group of 30 demographically matched healthy controls were tested. ADHD patients showed significant reductions of working memory storage capacity of a moderate to large effect size. Perceptual processing speed, task-based, and spatial selection were unaffected. The results imply a working memory deficit as an important source of behavioral impairments. The theory of visual attention parameter working memory storage capacity might constitute a quantifiable and testable endophenotype of ADHD.

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In recent years the amount of adults claiming to have a neuropsychological disorder increased dramatically, raising the suspicion that some of them may malinger symptoms for secondary gain, such as receiving compensation or drugs. Hence, valid diagnostic tools in the assessment of neuropsychiatric conditions are of great interest. In our experiment, we investigated whether adults feigning symptoms of Attention-deficit/hyperactivity disorder (ADHD) can be successfully detected by an assessment based on the ‘theory of visual attention’, namely TVA[Bundesen, C. (1990). A theory of visual attention. Psychological Review 97, 523-547]. Therefore, we provided healthy adults with information about ADHD (available on the internet) and instructed them to feign symptoms on self-report scales, as well as on the whole report of TVA, which provides an quantitative, parametric measure of the affected and preserved attentional functions of ADHD adults. Our results show that malingerers were indeed able to feign symptoms on the conventional questionnaires, but not capable of imitating the specific response pattern on the whole report of TVA that ADHD patients show. We found a sensitivity of 80 % and a specificity of 93 % for the whole report of TVA. Beyond the detection of adults malingering ADHD, TVA may also help to identify adults feigning symptoms of other neuropsychological disorders.