Birgit Mathes

Are oscillatory brain responses generally reduced in schizophrenia during long sustained attentional processing

Deficits in sustained attention and vigilance were assessed for oscillatory delta, theta, alpha, and gamma EEG activity during an auditory continuous performance task in patients with schizophrenia and healthy controls by quantifying peak-to-peak amplitudes of averaged and single-trial data. Averaged data indicated significantly reduced amplitudes in schizophrenia patients in all analyzed frequency bands, mainly at anterior locations. Single-trial analysis suggested that the amplitude reductions observed in the averaged delta, theta, and alpha response in patients originated from increased inter-trial phase variability. Gamma activity maximum amplitudes were reduced at the single-trial level. The findings imply that EEG activity in patients with schizophrenia can be characterized by multiple deficits in oscillatory networks, which indicates a disturbance in the temporal integration and interaction of all frequency components and their inter-trial variability.

Altered oscillatory alpha and theta networks in schizophrenia

In the present study we used a simple visual evoked potential and a visual oddball paradigm to investigate alterations in the temporal integration of different frequency components such as alpha and theta oscillations in patients with schizophrenia. We found that neither the amplitude enhancement after stimulus onset nor the intertrial phase coherence was generally reduced in patients, but that the topography of the neural response was altered. While healthy controls elicited their maximum early alpha as well as late theta response over posterior electrode sites, the maximum response in patients was shifted to anterior electrode positions. This result was not found for the late theta response for targets as target processing was accompanied with frontal theta amplitude enhancement in healthy controls as well. The change of the topographical response pattern was mirrored by the intertrial phase coherence in both frequency bands. The findings imply that schizophrenia is related to multiple alterations in oscillatory networks. Even during simple tasks without high cognitive demands dysfunctional mechanisms of temporal and regional coordination appear to be of importance in schizophrenia.

Voluntary control of Necker cube reversals modulates the EEG delta- and gamma-band response

Reversible figures such as the Necker cube make up a well-known class of visual phenomena in which an invariant stimulus pattern gives rise to at least two different perceptual interpretations. Former EEG studies of our research group demonstrated a reversal-related delta response and a frontal enhancement of gamma activity during multistable perception which has been interpreted as signaling attentional top-down processes. The aim of the present study was to investigate the functional involvement of delta and gamma activity in top-down processes more explicitly by asking 21 healthy participants to bring the reversal rate under voluntary control during viewing of the Necker cube. Slowing down the reversal rate should be accomplished by focussing attention to the currently perceived alternative while speeding up should be accomplished by shifting attention as rapidly as possible from one perspective to the other. EEG was recorded from frontal, central, parietal, and occipital locations of both hemispheres. The data was analysed on the single-sweep level in the delta and gamma frequency range. The results showed that both delta response and gamma power were larger during slowing down than speeding up the reversal rate. These findings may indicate that more attentional resources have to be allocated by the cognitive system in order to prevent a reversal by means of focussed attention than to initiate a reversal by attentional shifts.

The electrophysiological correlate of contour integration is modulated by task demands.

Psychophysical studies demonstrated under which task conditions contour integration based on orientation cues succeeds or fails. We investigated how the electrophysiological correlate of contour integration is modulated by changes in task demands. In two experiments, event-related potentials (ERPs) were recorded. We presented open or nearly closed contours defined by Gabor elements embedded in a background of randomly oriented distracters. In experiment 1, randomly oriented Gabors preceded the test stimulus, while in experiment 2, the screen was blank before appearance of the test stimulus. Correct performance was above 96% for aligned and slightly misaligned contours but did not significantly differ from chance level for random orientations of the contour elements. Detectable contours elicited a negative shift over posterior recording sites. This effect started about 150 ms after stimulus onset but was delayed for more difficult contour integration. Presenting the stimulus after a random display elicited a frontal selection positivity (FSP). In both experiments, contours elicited a P3, which was larger for aligned compared to misaligned contours. Timing, duration and localisation of the negative enhancement were similar to both the texture segmentation VEP (tsVEP) and the selection negativity (SN). Our results indicate that contours are processed similar to textures and that decreasing saliency of detectable contours is compensated by increasing processing time which possibly results from increasing allocation of visual selective attention.

Early processing deficits in object working memory in first-episode schizophreniform psychosis and established schizophrenia

BACKGROUND While there are many studies showing working-memory deficits in schizophrenia there are only a few that disentangle impairments for working-memory subprocesses such as perceptual, attentional, mnemonic and executive function. METHOD In this study of delay-dependent memory, 55 patients with schizophreniform psychosis, 50 with established schizophrenia and 56 healthy controls were investigated. Using the delayed matching-to-sample task from the Cambridge Neuropsychological Test Automated Battery (CANTAB), performance deficits were found in both patient groups after controlling for age and pre-morbid IQ. RESULTS Even after controlling for simultaneous matching-to-sample ability (i.e. perceptual matching), impaired performance in both patient groups was found as soon as the stimuli were no longer present. Impaired performance was not due to different types of errors in patients versus controls. Performance in both patient groups was comparable, except for a slight decrease of overall task performance. This suggests that the deficit is relatively stable during the course of the illness. CONCLUSIONS Our results suggest a deficit in patients with psychotic illness in the initial processes necessary to actively maintain information, such as the ability to form an internal representation of complex objects.

Medial temporal lobe activity at recognition increases with the duration of mnemonic delay during an object working memory task.

Object working memory (WM) engages a disseminated neural network, although the extent to which the length of time that data is held in WM influences regional activity within this network is unclear. We used functional magnetic resonance imaging to study a delayed matching to sample task in 14 healthy subjects, manipulating the duration of mnemonic delay. Across all lengths of delay, successful recognition was associated with the bilateral engagement of the inferior and middle frontal gyri and insula, the medial and inferior temporal, dorsal anterior cingulate and the posterior parietal cortices. As the length of time that data was held in WM increased, activation at recognition increased in the medial temporal, medial occipito‐temporal, anterior cingulate and posterior parietal cortices. These results confirm the components of an object WM network required for successful recognition, and suggest that parts of this network, including the medial temporal cortex, are sensitive to the duration of mnemonic delay. Hum Brain Mapp 2007.

Occipital gamma response to auditory stimulation in patients with schizophrenia

This study investigated changes in gamma oscillations during auditory sensory processing (auditory-evoked gamma responses, AEGR) and target detection (auditory event-related gamma responses, AERGR) in healthy controls (n=10) and patients with schizophrenia (n=10) using both single-trial and averaged time-frequency data analysis. The results show that single-trial gamma responses in patients were altered in magnitude and topographic pattern for both the AEGR and the AERGR experimental conditions, whereas no differences were found for the averaged evoked gamma response. At the single-trial level, auditory stimuli elicited higher gamma responses at both anterior and occipital sites in patients with schizophrenia compared to controls. Furthermore, in patients with schizophrenia target detection compared to passive listening to stimuli was related to increased single-trial gamma power at frontal sites. In controls enhancement of the gamma response was only apparent for the averaged gamma response, with a distribution largely restricted to anterior sites. The differences in oscillatory activity between healthy controls and patients with schizophrenia were not reflected in the behavioral measure (i.e., counting targets). We conclude that gamma activity triggered by auditory stimuli in schizophrenic patients might have less selectivity in timing and alterations in topography and may show changes in amplitude modulation with task demands. The present study may indicate that in patients with schizophrenia neuronal information is not adequately transferred, possibly due to an over-excitability of neuronal networks and excessive pruning of local connections in association cortex.

Dissociation of reversal- and motor-related delta- and alpha-band responses during visual multistable perception

Multistable visual perception refers to phenomena, in which one invariant stimulus pattern is perceived in at least two different, mutually exclusive ways. In this EEG study we differentiate between perceptual- and motor-related processes during perceptual reversals. Delta- and alpha-band activity was analyzed while participants answered to a perceptual reversal either immediately or with a delay of approximately 1500 ms, thereby separating reversal-related and motor-related activity. On the single sweep level a reversal-related positive delta response and reversal-related desynchronisation of alpha activity could be detected irrespective of the motor response. Both conditions elicited the strongest reversal-related modulations at posterior locations. Contrary, motor-related responses were found predominantly at central locations. These findings were supported by a control experiment, using a slightly modified stimulus that allowed unambiguous perceptual changes to be triggered exogenously. In conclusion, this study demonstrates that the brain response to perceptual reversals differs from motor-related processes elicited by the button press indicating the perceptual reversal. The results of this study, therefore, indicate that perceptual- and motor-related processes are achieved in multiple selectively distributed and parallel working oscillatory networks of the brain.

Auditory-evoked alpha oscillations imply reduced anterior and increased posterior amplitudes in schizophrenia

OBJECTIVE Most of the work on disturbed oscillatory activity during auditory tasks in schizophrenia has focused on reduced gamma oscillations at fronto-central sites. Recent studies of our group, however, indicate a more general disturbance affecting the spatial distribution of oscillatory brain activity of gamma as well as slow frequencies, such as alpha oscillations. METHODS During a passive auditory listening task, electroencephalography was recorded from healthy controls and patients with schizophrenia. Stimulus-locked alpha activity within the first 250 ms after stimulus onset was analyzed from midline electrodes. RESULTS Healthy controls showed the common fronto-central maximum of the early alpha response, while patients with schizophrenia showed lower fronto-central and larger parieto-occipital alpha activity than controls, leading to a more similar amplitude distribution across the midline electrode sites. CONCLUSIONS The present results indicate malfunctioning long-range inhibition of task-irrelevant cortical areas in schizophrenia, which may disturb functional integration of perception and attention. We emphasize the importance of the whole-brain network theory for the understanding of schizophrenia since it proposes that integrative brain function is based on the coexistence and cooperative action of many interwoven and interacting sub-mechanisms. SIGNIFICANCE Neuropsychiatric illnesses such as schizophrenia are marked by communication and coordination failures between different brain regions and different frequency bands.

Alpha Brain Oscillations and Inhibitory Control

A major challenge for developmental cognitive neuroscience is to understand how changes in cognitive functions related to aging are associated with changes in the neuronal information processing architecture. Previous studies on EEG event-related brain oscillations suggest functional changes in alpha-bands with age during sensory and memory tasks. Specifically, the topographical distribution of both single-trial lower and upper alpha magnitude and the corresponding phase coherence is altered in elderly persons. Thus, alpha oscillations, associated not only with sensory, but also with sensorimotor functions, may be altered with age. Compensatory mechanisms, possibly reflected in increased frontal alpha synchronization, may thereby be of profound relevance. The present study investigates age-related differences in the modulation of alpha oscillatory activity related to sensory and sensorimotor functions, including response preparation, execution, and inhibition. EEG was recorded while 10 young and 10 elderl...