Theresa Schreppel

The other-race effect for face perception: an event-related potential study

SummaryIt is well known that a recognition bias can be observed whenever subjects have to decide whether they have seen a person before that belongs to a different ethical group. Although this “other-race effect” is well documented on a behavioural level, its underlying mechanisms remain unclear. One plausible explanation might be that cortical areas involved in face processing are not as effective for other-race faces due to a missing experience with individuals from other ethnical groups. This interpretation is strongly supported by a functional magnetic resonance imaging study showing decreased brain activity on other-race faces. Furthermore, two event-related potential studies revealed differences in brain activity in the first 250 ms after face presentation, but with inconsistent results. Therefore, we investigated 12 Caucasian subjects, showing them faces of Asian and Caucasian subjects in a perceptual priming paradigm and measured the event-related brain potentials. On a behavioural level we found slower reaction times to Asian faces compared to Caucasian faces in the unprimed condition, reflecting a deficit for Caucasian subjects to process other-race faces. In accordance with these behavioural data we see a significantly reduced late N250r amplitude in the unprimed condition to the Asian faces compared to the Caucasian faces. These results clearly indicate that the other-race effect was present in our sample and very specific only in the unprimed condition around 350–450 ms after stimulus onset.

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.

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.

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 pro- cesses 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.

D4 receptor gene variation modulates activation of prefrontal cortex during working memory.

It has been shown that dopamine (DA) influences performance on neurocognitive tests, which are thought to rely on prefrontal activity. The purpose of this study was to explore the effects of gene polymorphisms related to DA activity, namely the D4 DA receptor (DRD4) gene exon III polymorphisms, on prefrontal cortex (PFC) activation. In this study we measured the brain oxygenation of the PFC during an n‐back task with near‐infrared spectroscopy (NIRS). We investigated 40 young healthy subjects, 12 of which carried the DRD4 exon III 7‐repeat allele (group 7). These were compared with subjects without a 7‐repeat allele (n = 28, group 4). Additionally, we compared good and bad performers with respect to brain activation. As expected, we found significant increases in the concentration of oxygenated haemoglobin [O2Hb] during the 1‐back and 2‐back condition compared with baseline, and a corresponding significant decrease of deoxyhaemoglobin concentration. As a main result of this study we also found an interaction effect between task condition and DRD4 genotype with higher increases of [O2Hb] during the 2‐back version compared with the 1‐back version for the subjects of the 7‐repeat allele group only. The same effect was seen as a statistical trend, when we compared bad performers with good performers. Therefore, we interpret the effects of the 7‐repeat allele group of DRD4 as a sign of ineffective brain activity, perhaps even as a sign of prefrontal noise.

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.

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.

The impact of prefrontal cortex for selective attention in a visual working memory task.

In this study, a variant of the n-back task was used to investigate electrophysiological correlates of top-down processes in visual-object working memory. Event-related potentials were used to replicate results concerning an attention related modulation of neural processes and to investigate the involvement of prefrontal cortex in this modulation. 16 healthy subjects executed an n-back task with sequentially presented faces and scenes. Attention was selectively directed to only one stimulus category. We found an enhancement of the N170 amplitudes for relevant stimuli compared to irrelevant or neutral stimuli. Late frontal amplitudes were stronger positive for relevant compared to neutral stimuli indicating selective attention processes of working memory. Evidence for selective inhibition was not found.

Contents Vol. 57, 2008

N. Brunello, Milan G. Erdmann, Berlin S. Galderisi, Naples U. Hegerl, Leipzig K. Hirata, Tochigi Y. Koga, Tokyo J. Kornhuber, Erlangen P.T. Loosen, Nashville, Tenn. D. Lehmann, Zürich K.P. Lesch, Würzburg G.N. Papadimitriou, Athens M. Reuter, Bonn F. Rösler, Marburg G. Ruigt, Oss J.K. Rybakowski, Poznan F. Schneider, Aachen D. Souery, Brussels P. Willner, Swansea H. Yoneda, Osaka Associate Editors