Deficits in executive functions, e.g. voluntary selection, are considered central to the attention-deficit/hyperactivity disorder (ADHD). The aim of this simultaneous EEG/fMRI study was to examine associated neural correlates in ADHD patients. Patients with ADHD and healthy subjects performed an adapted go/nogo task including a voluntary selection condition allowing participants to freely decide, whether to press the response button. Electrophysiologically, response inhibition and voluntary selection led to fronto-central responses. The fMRI data revealed increased medial/lateral frontal and parietal activity during the voluntary selection task. Frontal brain responses were reduced in ADHD patients compared to controls during free responses, whereas parietal brain functions seemed to be unaffected. These results may indicate that selection processes are related to dysfunctions, predominantly in frontal brain regions in ADHD patients.

The concept of 'willed' actions has attracted attention during the last few years. Free choices have been associated with activations on the medial frontal surface, the dorsolateral prefrontal cortex and the parietal lobe. Self-paced movements and free selection between various motor responses were typically used to investigate voluntary behavior. The aim of the present study was to determine neural correlates of voluntary motor responses and the voluntary inhibition of motor responses in a group of healthy subjects. Hence, a go/nogo/voluntary selection paradigm was used. In the voluntary selection condition subjects decided freely whether or not to respond with a button press after stimulus presentation. Functional MRI data and event-related potentials were acquired simultaneously in order to reliably investigate spatial and temporal characteristics of these responses. The results showed decision-related enhanced neural responses predominantly in the medial frontal gyrus/supplementary motor area, lateral frontal brain regions and the inferior parietal gyrus. Additional activations associated with voluntary movements were detected in the frontal eye field as well as brain regions directly linked to motor responses (e.g. somatosensory cortical areas). Altogether, decision processes were shown to be relatively independent of the kind of response chosen.

Deficits in executive functions, including voluntary decisions are among the core symptoms of attention deficit/hyperactivity disorder (ADHD) patients. In order to clarify the spatiotemporal characteristics of these deficits, a simultaneous EEG/functional MRI (fMRI) study was performed. Single-trial coupling was used to integrate temporal EEG information in the fMRI analyses and to correlate the trial by trial variation in the different event-related potential amplitudes with fMRI BOLD responses. The results demonstrated that during voluntary selection early electrophysiological responses (N2) were associated with responses in similar brain regions in healthy participants as well as in ADHD patients, e.g., in the medial-frontal cortex and the inferior parietal gyrus. However, ADHD patients presented significantly reduced N2-related BOLD responses compared to healthy controls especially in frontal areas. These results support the hypothesis that in ADHD patients executive deficits are accompanied by early dysfunctions, especially in frontal brain areas.

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Executive functions comprise various cognitive abilities including the inhibition of prepotent responses and voluntary decisions. Several studies showed medial-frontal activations in tasks with the free selection of responses. The inhibition of prepotent response tendencies seems to be associated with medial frontal as well as lateral frontal BOLD responses. The aim of this simultaneous EEG and fMRI study was to discriminate the neural correlates of behavioural control processes in ADHD.