Search

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.8 adults with ADHD and 8 matched healthy subjects performed a go/nogo task comprising three different conditions: during the go condition, subjects were instructed to press a response button as fast as possible; during the nogo condition, this response was to be inhibited. In the voluntary selection task participants were allowed to freely decide, whether to press the response button or not.The fMRI protocol used a gradient-echo EPI pulse sequence. Further analyses were done with using the BrainVoyager software package (Goebel, Maastricht). EEG signals were simultaneously recorded (Brain Products, Munich).Electrophysiologically, the nogo task and voluntary decision task led to a negative decline especially in fronto-central brain regions (N2) in both groups. Regarding the functional MRI data we found inhibition-associated BOLD responses especially medial-frontal in the pre-SMA and activations in the medial part of BA 8 for the voluntary selection. ADHD patients showed a reduced contribution of frontal brain regions during free responses compared to controls.The results may indicate that selection processes are related with dysfunctions predominantly in frontal brain regions in ADHD patients.

IntroductionPatients with impulse control deficits often show cognitive abnormalities especially in executive abilities. One possibility to examine the underlying neurophysiological mechanisms is to assess evoked potentials. In the present study an adapted go/nogo-paradigm was used to investigate electrophysiological correlates of voluntary selection and behaviour control processes in patients suffering from alcohol dependence and attention deficit hyperactivity disorder (ADHD).Methods15 patients with alcohol dependence, 15 adult patients with ADHD and 15 control persons were included into the study. Patients with alcoholism were examined twice: before and after an inpatient detoxification.The participants performed a go/nogo task, comprising three different conditions:Apart from the go-condition (button press required) and the nogo-task (inhibition of a behavioural response), a voluntary selection task was included in which participants were allowed to freely decide, whether to press the response button or not.Results and discussionResponse inhibition and voluntary selection processes were related to a fronto-central negativity after 200 ms (N2) and a positivity after 300 ms (P3) in healthy subjects. In patients, the P3 amplitude was reduced compared to the controls. In addition, alcohol dependent patients did not show a N2 potential.The results indicate fronto-central dysfunctions dysfunctions in either patient group. However, different neuronal processes seemed to be affected in patients with ADHD and patients with alcoholism.