Bernardina M. Wieringa

Discrepant target detection and action monitoring in obsessive–compulsive disorder

Obsessive-compulsive disorder (OCD) has been related to altered mechanisms of action monitoring and target detection, and it has been hypothesized that hyperactive striatal-cortical circuits constitute the underlying pathophysiology. This study used event-related brain potentials (ERPs) to explore this hypothesis. A choice reaction time experiment was carried out in a group of OCD patients and a normal comparison group. The P3b component of the ERP to targets was taken as an indicator of the target-evaluation process and the response-locked error-related negativity (ERN) served as an indicator of action monitoring. We hypothesized that the OCD group would show a shortened P3b latency and an amplitude-enhanced ERN. Consistent with our expectations, the P3b latency was shorter and the ERN amplitude was higher in the OCD group. Unexpectedly, we also observed a prolonged ERN latency in the OCD group and a more posterior topography of this component. The data provide partial support for the hypothesis of a hyperactive neural network in OCD. In addition the disorder must involve pathophysiological processes that are presumably related to other aspects of its complex and heterogeneous clinical hallmarks.

Brain potentials reveal the timing of face identity and expression judgments

Event-related brain potentials (ERPs) were recorded from multiple scalp locations from young human subjects while they performed two different face processing tasks. The first task entailed the presentation of pairs of faces in which the second face was either a different view of the first face or a different view of a different face. The subjects had to decide whether or not the two faces depicted the same person. In the second task, pairs of faces (frontal views) were presented with the task of judging whether the expression of the second face matched that of the face. Incongruous faces in the view (identity) matching task gave rise to a negativity peaking at about 350 ms with a frontocentral maximum. This effect was similar to the N400 obtained in linguistic tasks. ERP effects in the expression matching task were much later and had a different distribution. This pattern of results corresponds well with neuropsychological and neuroimaging data suggesting specialized neuronal populations subserving identity and expression analysis but adds a temporal dimension to previous investigations.

Altered inhibition of motor responses in Tourette Syndrome and Obsessive-Compulsive Disorder.

Objectives– The Gilles de la Tourette Syndrome (TS) and Obsessive Compulsive Disorder (OCD) have been shown to display impaired cognitive and motor inhibition. This study investigated inhibitory mechanisms of motor responses in order to expand the understanding of sensorimotor integration processes in both disorders. We hypothesized that both patient groups would display altered frontal inhibitory activity. Material and methods– To this end event‐related brain potentials (ERPs) were recorded in a STOP‐paradigm in groups of TS and OCD patients and in a control group. The paradigm required the execution of a motor response after a “go” signal was given and the occasional suppression of this response after a second “stop” signal occurred. Results– Behavioral parameters and Lateralized Readiness Potential (LRP) confirmed that both patient groups were well able to initiate motor responses. “Go” and “stop” stimuli elicited an enhanced frontal negative activity in both patient groups. In addition, “stop” stimuli were associated with a frontal shift of the NoGo‐Anteriorization (NGA) in the TS group but not in the OCD group. Conclusions– The data are interpreted to indicate altered frontal inhibitory functions. Similarities and dissimilarities between the findings for TS and OCD are discussed with respect to other pathophysiologic aspects of the disorders.

Differential Effects of Emotional Content on Event-Related Potentials in Word Recognition Memory

The aim of this study was to delineate the influence of the emotional content of stimuli to be remembered on the recognition performance of normal subjects by means of the event-related potential (ERP) technique. When words are presented repeatedly, brain responses to repeated and recognized items are characterized by a more positive waveform, referred to as ‘old/new effect’. Words judged for their emotional connotation (‘negative’, ‘positive’ and ‘neutral’) were presented successively on a video monitor to subjects, who had the task to indicate whether a given word occurred for the first (‘new’) or second (‘old’) time within the list by pressing one of two buttons. For each word category, the ERPs of the old words were more positive compared to those of the new items from about 250 ms after stimulus. The old/new effect was significantly enhanced for the negative and positive items compared to the neutral stimuli between 450 and 650 ms after stimulus pointing to a significant influence of the emotional content of words on verbal memory processes. This paradigm appears to be feasible to investigate interactions of emotion and cognition in psychiatric patients.

Human brain potentials to reading syntactic errors in sentences of different complexity

In order to determine if an event-related brain potential (ERP) effect described for syntactic violations (P600/SPS) varies with the amount of reprocessing entailed by a violation, number incongruencies were presented either within simple declarative or within subordinate clauses. ERPs were recorded while 12 German subjects read the stimulus materials presented word by word on a video monitor. The ERPs showed a P600/SPS effect for all sentence types, which was smallest in amplitude and earliest in latency for simple declarative sentences. This effect therefore qualifies as a metric for the amount and timing of syntactic reprocessing entailed by a syntactic error. In addition, a late frontal negativity (1000-1400 ms range) was found for the simple declarative sentences.

Alteration of early components of the visual evoked potential in amyotrophic lateral sclerosis

Abstract Evoked potentials were recorded in three different visual experiments in 14 patients with amyotrophic lateral sclerosis (ALS) and 14 matched control subjects. Control subjects’ evoked potentials (EPs) were characterized by an initial positivity in the 90–140 ms range (P1) at the temporo-occipital site. This component was absent from the group average of the ALS patients as well as the individual patients’ EPs. As the P1 is known to emanate from inferior occipito-temporal areas, this finding provides electrophysiological evidence for a cortical involvement in ALS including visual areas.

EVENT-RELATED BRAIN POTENTIALS TO UNFAMILIAR FACES IN EXPLICIT AND IMPLICIT MEMORY TASKS

The purpose of this study was to investigate electrophysiological correlates related to the recognition of repeated faces in the intact human by means of event-related brain potentials (ERPs). A group of young healthy adults performed a continuous face recognition task, in which 240 unfamiliar faces were flashed upon a computer screen with 80 of the faces being repetitions. The subjects had to classify faces as previously seen and previously unseen faces. The concomitantly recorded ERPs from 19 scalp sites revealed a more positive going waveform for the correctly classified repeated faces beginning at about 280 ms (old/new effect). The same subjects performed a similar task with visually presented concrete nouns as stimuli. The old/new effect in this task showed a similar distribution, amplitude and onset latency. It is thus concluded that the old/new effect is not specific to the materials to be memorized. In contrast, the old/new effect in an implicit face repetition experiment (with the detection of famous persons being the task) showed a different distribution. It is argued that the differential distribution might reflect the different requirements of the two tasks (explicit vs. implicit task). Recent interpretations of the old/new effects are discussed.

Human evoked potentials to long duration vibratory stimuli: role of muscle afferents

Tonic vibratory stimuli of 1000 ms duration and different frequencies were delivered to muscles of the forearms of young human subjects. Evoked potentials (EPs) were recorded from 29 scalp channels and revealed phasic highly lateralised and focally distributed EPs during the first 100 ms of the recording epoch that could be adequately modelled with a single point dipole source located in the vicinity of the central sulcus contralateral to the stimulated arm. A later negativity with an onset of about 400 ms and a duration of about 800 ms was found to be symmetrically distributed over fronto-central regions. This negativity is interpreted in terms of cortical activation beyond the primary sensory fields and could be related to the kinaesthetic phenomena experienced during muscle vibration.

Differential effects of two motor tasks on ERPs in an auditory classification task: evidence of shared cognitive resources.

The aim of the study was to assess cognitive demands and fatigue during the execution of two different motor tasks. Event-related brain potentials (ERPs) were recorded from 15 healthy subjects while they concurrently performed, (1) one of two motor tasks, and (2) a three stimulus (70% standard tones, 15% target tones, 15% novel stimuli) auditory classification task. Both motor tasks required the externally paced adduction of the right thumb with the force task requiring a precise movement (feedback given) with about 50% of maximum force output (6 s on task, 4 s rest) while the displacement task required the same precise movement with only minimal force requirements. In separate sessions, both tasks were performed for about an hour with the subjects concurrently paying attention to the auditory task with button presses required for the target stimuli. This provided a dual task situation with trade-offs in P3b amplitude as a function of difficulty of the primary (motor) task. The P3b to the auditory target stimuli was reduced during the force session compared to the displacement session, indicating that the force-task placed a higher demand on cognitive resources. No differential effect of fatigue (time on task) could be ascertained over six consecutive parts of the session. The P3a component, a putative correlate of orienting of attention, showed a rapid attenuation over time but, attesting to its automatic nature, no effect of concurrent motor task. ERP components recorded timelocked to the movements showed a marked difference between the two tasks with the displacement task giving rise to higher amplitudes. Moreover, only for the force task an influence of time on task (fatigue) on the MP was found. The dual task methodology is a potentially useful tool to disentangle cognitive and motor components of central fatigue.

Recognition memory deficits in amyotrophic lateral sclerosis assessed with event-related brain potentials

Objectives ‐ Amyotrophic lateral sclerosis (ALS) has been shown to cause neuropsychological deficits. The present investigation sought to delineate memory deficits by recording cognitive event‐related potentials (ERPs). Subjects and methods ‐ Eight ALS patients and 8 matched controls were subjected to a 2‐phase recognition memory test. During the first phase words were presented consecutively on a video‐screen with one‐third of the words being repeated. The subject had to press buttons according to whether a word had been repeated or not. During the second phase (delay 1 h) a second list containing 33% old items from phase 1 and 66% new words was shown with an old/new decision required. Results ‐ ALS patients showed less accurate recognition in the second phase. The ERPs of the controls showed a reliable difference between old and new items in both phases. This difference was nearly absent in the patients in both phases. Conclusion ‐ The ERP pattern suggests abnormal memory processes in ALS. The results are compared with data from similar experiments in Huntingtons and Alzheimers disease and are interpreted in terms of an encoding deficit in ALS.