Peter Scheuerpflug

Altered response control and anterior cingulate function in attention-deficit/hyperactivity disorder boys

OBJECTIVE To investigate mechanisms and structures underlying prefrontal response control and inhibition in boys suffering from attention-deficit/hyperactivity disorder (ADHD). METHOD Sixteen boys with ADHD and 19 healthy controls were investigated electrophysiologically during performance of a visual Go-Nogo task (Continuous Performance Test, CPT). An electrophysiological source localization method was employed to further analyze the data. RESULTS The ADHD boys showed a significantly diminished central Nogo-P3, due to a lack of Nogo-related frontalization of the positive brain electrical field in this group. This two-dimensional effect was associated with a significantly reduced activation of the anterior cingulate cortex (ACC) in the ADHD boys in the Nogo condition of the CPT. Both groups did not significantly differ regarding the amplitude of the Nogo-N2. CONCLUSIONS The results indicate deficits in prefrontal response control in unmedicated ADHD boys that do not seem to be specifically inhibitory in nature. A supposed dysfunction of the ACC in ADHD was confirmed.

Multicenter P300 Brain Mapping of Impaired Attention to Cues in Hyperkinetic Children

OBJECTIVE To measure specific neurophysiological attention deficits in children with hyperkinetic disorders (HD; the ICD-10 diagnosis for severe and pervasive attention-deficit/hyperactivity disorder [ADHD]). METHOD In a multicenter sample of 148 children with HD and control children aged 8 to 14 years, event-related potential maps were recorded during a cued continuous performance test (A-X/O-X). Maps to cues (requiring attention but no response) and distractors and performance were tested for differences between age- and sex-matched HD and control groups (n = 57 each), as well as between clinics (n = 5). RESULTS The N1, P3a, and P3b maps revealed reliable attention effects, with larger amplitudes after cues than after distractors, and only minor differences across clinics. Children with HD missed more targets, made more false alarms, and had larger N1 followed by smaller P3b amplitudes after cues than did controls. Cue-P3b amplitude correlated with detecting subsequent targets. Cue-P3b tomography indicated posterior sources that were attenuated in children with HD. CONCLUSIONS Brain mapping indicates that children with HD attend to cues (preceding potential targets) with increased initial orienting (N1) followed by insufficient resource allocation (P3b). These multiple, condition-specific attention deficits in HD within 300 msec extend previous results on ADHD and underline the importance of high temporal resolution in mapping severe attention deficits.

Far field potentials from the brain stem after transcutaneous vagus nerve stimulation

Summary. Recently, the vagus nerve has gained particular interest in neuropsychiatry, as neurodegenerative diseases like Alzheimer’s and Parkinson’s disease are supposed to affect the brainstem nuclei of the vagus nerve early in their course. In addition, electric stimulation of the vagus nerve has therapeutic effects in otherwise therapy-refractory epilepsies and depressions. So far, no method is available to assess vagus nerve function in this context. On this background and based on the established techniques of early acoustic evoked potentials we investigated if a transcutaneous electric stimulation of the sensory auricular branch of the vagus nerve innervating parts of the outer ear is feasible in healthy subjects using this hypothesis-generated approach. We were able to record a clear, reproducible Vagus Sensory Evoked Potential (VSEP) measured as far field potential probably originating in vagus nuclei in the brainstem. Further studies are needed to test the interindividual stability and test-retest reliability of this new method before potential diagnostic and therapeutic applications might be evaluated.

Electrophysiological investigation of the effectiveness of methylphenidate in children with and without ADHD

Summary. The Continuous Performance Test (CPT) is an appropriate instrument for assessment of correlates at the brain electrical activity level of attention and response to stimulant medication. The aim of the study was to confirm at the electrophysiological level the clinical effectiveness of methylphenidate (MPH) in children with attention deficit / hyperactivity disorder (ADHD); to this end, a comparative study of hyperactive and healthy control children was undertaken, employing a modified CPT test.Twenty-one channel ERPs from 17 hyperactive boys, with and without MPH treatment, and from 20 healthy control children were analyzed with reference-independent techniques. The resulting quasi-stabile microstates correspond to the time ranges of the conventional ERP components P100, P200 and P300 (with the subcomponents P3a and P3b) and could be discriminated by means of data-based segmentation. The P3a amplitudes of the hyperactive children, in each case with and without MPH medication, were compared with those of healthy controls.P3a segment amplitudes were significantly lower in non-medicated ADHD patients than in healthy children, both following positive and inhibitory stimulus conditions. A significant medication effect was detected following MPH treatment: segment 3 amplitudes in MPH-treated hyperactive children were not significantly different from those of healthy controls.MPH exerts a highly potent effect on stimulus recognition and resulting consequences. Application of the CPT-OX enables the reliable measurement of electrophysiological correlates of the clinical effectiveness of MPH under different stimulus conditions.

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.

Stability of late event-related potentials: topographical descriptors of motor control compared with the P300 amplitude.

The P300-amplitude evoked with an acoustic oddball-paradigm is considered the most stable late event-related potential (ERP). This amplitude-index has become a standard parameter in electrophysiology. Recently, a robust ERP-parameter (NoGo-anteriorization, NGA) has been introduced, which reflects spatial brain electrical changes in relation to execution and inhibition of a motor response elicited with a Continuous Performance Test (CPT). The current study refers to the stability of this new topographical ERP-parameter compared to the stability of the classical P300-amplitude. For that purpose, 12 healthy subjects were investigated with both paradigms during recording of a 21-channel EEG. Analysis of the resulting ERPs revealed a very high stability for both, topographical and amplitude index: In every single subject, the brain electrical fields were characterized by a more anterior location in the NoGo- compared to the Go-condition (=NGA) and by higher amplitudes after target compared to distractor condition. T-tests, analyses of the effect size and of the power revealed equivalent differences between the two contrasting conditions for the topographical compared to the amplitude index. These results indicate that the stability of the topographical ERP-parameters elicited with the CPT is sufficient for an electrophysiological standard-index. The possibility to elicit a robust and specific spatial brain activation with the CPT is an ideal completion to the classical P300 amplitude effect and, therefore, hopefully will be a useful expansion of the standard paradigms in electrophysiological laboratories.

Visual information processing in dyslexic children

OBJECTIVE Several studies presented evidence for magnocellular deficits in dyslexics both in behavioural as well as in electrophysiological data of local electrode sites. We investigated two well-known paradigms (motion-onset and random-dot-kinematogram) with regard to global electrophysiological parameters. METHODS Twenty-one-channel event-related potentials (ERPs) of 16 dyslectic and 15 control children were analyzed with reference-independent methods. For each paradigm quasi stable microstates were identified by means of a data-driven segmentation procedure and compared between both groups. RESULTS Differences in global ERP responses between dyslexic and control children could be found for rapid moving gratings but not for the dot coherence. CONCLUSIONS Dyslexic children seem to have some highly specific visual deficits in processing moving stimuli. These deficits can be related to the magnocellular system.

Optical Topography with Near-Infrared Spectroscopy During a Verbal-Fluency Task

Abstract: In this study we investigated the changes in brain oxygenation in 22 subjects during a verbal fluency task (VFT) using multichannel near-infrared spectroscopy (NIRS). To assess topographical effects in more detail we measured over bilateral prefrontal and over the left frontolateral cortex in 11 subjects. We found significantly higher increases in O2HB, as a sign of cerebral activation, during the VFT compared to a verbal repetition control task over the left prefrontal and the inferior left lateral brain areas. These results underscore the value of NIRS to assess functional brain activation during cognitive tasks. Furthermore, it shows the advantage of multichannel compared to previously used single channel NIRS measurements.

Changes of the brain electrical fields during the continuous performance test in attention-deficit hyperactivity disorder-boys depending on methylphenidate medication

OBJECTIVE The continuous performance test (CPT) is successfully applied to evaluate attentional performance in attention-deficit hyperactivity disorder (ADHD)-children. The aim of the present study was to investigate the changes of the topographic P300-features in relation to methylphenidate-medication and to different attentional processes in primer- and distractor-conditions. METHODS Twenty-one-channel-ERPs of 17 ADHD-boys were analyzed with reference-independent methods. Four quasi stable microstates within the time frames of conventional P100, P200, P3a and P3b components were identified by means of a data-driven segmentation procedure. RESULTS In segment 3 topographical assessment yielded a significant occipital and right-shift of the positive centroid, longer centroid distance and higher amplitudes in primer- than in distractor conditions. MPH increased the amplitude and distance in primer and distractor-condition, without changing the topography. In segment 4 the electric field strength of distractor-conditions collapsed, whereas the primer condition showed a strong fronto-parietally oriented potential-field. There was a tendency to higher amplitudes due to MPH-medication. CONCLUSIONS These results indicate a robust neurophysiologic differentiation of cognitive processes. MPH activates an early (P3a) covert attention process indicated by increased amplitudes and centroid. No effects were seen in later processes. Based on these effects, we propose to use the amplitude- and distance-increase in microstate 3 as an indicator of MPH efficacy in ADHD-boys.

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.