The effect of ADHD symptoms on performance monitoring in a non-clinical population.

Recent studies suggested deficits in error processing in patients with Attention Deficit Hyperactivity Disorder (ADHD), but some inconsistencies are still present. Using the ADHD screening questionnaire, the Adult ADHD Self-Report Scale, we investigated the association between the amount of inattention and hyperactivity/impulsivity symptoms in a non-clinical population of healthy students (n=56) and the neural correlates of error processing measured with event-related potentials. We found reduced amplitudes of error-positivity (Pe) with increasing symptoms of inattention, but no correlation with error-related negativity. These results suggest that attention deficits reduce the conscious evaluation of an error as reflected by reduced Pe amplitudes.

Activation of the prefrontal cortex in working memory and interference resolution processes assessed with near-infrared spectroscopy.

BACKGROUND/AIMS: The present study investigated cortical correlates of top-down processes in visual-object working memory with multi-channel near-infrared spectroscopy. METHODS: The activity of the prefrontal cortex (PFC) was investigated while performing an n-back task with sequentially presented task-relevant and task-irrelevant faces. The activation patterns in the PFC associated with working memory and interference resolution were examined in 20 healthy adults. RESULTS: We found a bilateral enhancement of oxygenated haemoglobin in the lateral PFC for remembering relevant faces and in the right lateral PFC for ignoring irrelevant faces. Oxygenation for relevant and irrelevant faces did not differ significantly, indicating that memory processes and interference resolution were interdependent functions, which were subserved by comparable prefrontal regions. CONCLUSION: This supports the notion that the prefrontal activity during working memory tasks reflects not only maintenance processes but also attentional monitoring and selection processes.

Neural correlates of performance monitoring in adult patients with attention deficit hyperactivity disorder (ADHD).

INTRODUCTION: In this study, the neural correlates of error processing in adult patients with attention deficit hyperactivity disorder (ADHD) are to be investigated for the first time. Recent studies in children with ADHD suggested, with some inconsistencies, deficits in error processing. Based on an analogue study with students, we hypothesized that ADHD patients show reduced amplitudes in the event-related potential (ERP) of the Pe (error positivity) but normal amplitudes of the ERN (error-related negativity) after incorrect responses. METHOD: In this study we investigated 34 adult ADHD patients and 34 healthy controls with a modified version of the Eriksen flanker task while recording the neural activity with 26 scalp EEG electrodes. Patients discontinued all medication at least 3 days prior to investigation. Age was included as a control variable for the statistical analyses. RESULTS AND CONCLUSION: As hypothesized, we found reduced Pe amplitudes, but also reduced ERN values, in ADHD patients. Importantly, theses differences as well as the deficits in behavioural performance were mainly detectable in the younger subsample, but not in the elderly subsample. Our results indicate that adult ADHD patients are characterized by deficits in error processing, which vanish with age.

Emotional deficits in adult ADHD patients: an ERP study.

This study examined general deficits in positive stimuli evaluation in adults with Attention Deficit Hyperactivity Disorder (ADHD). We investigated the event-related potentials to positive, negative and neutral pictures in 32 adults with ADHD and 32 control subjects. For this study we measured 21 electrodes placed in accordance with the international 10-20 system and calculated the early posterior negativity (EPN), which physiologically is characterized by more negative values for emotional as compared to neutral stimuli. We found significantly reduced EPN values for the ADHD patients compared to the healthy controls, but only in the positive stimuli condition, without any significant differences in the negative stimuli condition. Our data indicate that ADHD patients show less reactivity to positive visual stimuli which might be relevant in the context of described dysfunctions of the motivational-reward system in ADHD.

Catechol-O-methyltransferase Val158Met genotype affects neural correlates of aversive stimuli processing.

It was previously shown that variation of the catechol-O-methyltransferase (COMT) gene modulates brain activity during the processing of stimuli with negative valence, but not for pleasant stimuli. Here, we tested whether the COMT genotype also modulates the electrophysiological correlates of emotional processing and explored whether the environmental factor of life stress influences this effect. Using the early posterior negativity (EPN) paradigm, event-related brain potentials were measured in 81 healthy individuals during the processing of pictures that evoked emotions of positive and negative valence. As was hypothesized, the COMT genotype affected the EPN amplitudes for unpleasant stimuli, but not for pleasant ones. Specifically, Met/Met carriers respond more sensitively to unpleasant stimuli, as compared with Val/Val carriers. We did not find evidence that life stress moderates the effect of the COMT genotype on emotional stimuli processing.

Brain activation for alertness measured with functional near infrared spectroscopy (fNIRS).

Alertness is a basic psychological function within the construct of attention. The neural basis of alertness has been found in the right frontotemporal cortex and the left ventrolateral prefrontal cortex. The aim of the present study was to establish the measurement of functional brain activity during alertness with functional near infrared spectroscopy (fNIRS). Therefore we measured the changes in brain oxygenation in two independent samples during an alertness condition and control conditions with 52 NIRS channels placed over the frontotemporal area. Based on a region of interest defined in the first sample (and on the literature) we showed in the second sample significantly higher activation during the alertness condition compared to the control conditions. This study proves the possibility of investigating the neural correlates of alertness using fNIRS.