Christina Schmiedt-Fehr

Event-related delta and theta brain oscillations reflect age-related changes in both a general and a specific neuronal inhibitory mechanism.

OBJECTIVE ERPs may be limited in validity when investigating inhibitory functions in later adulthood, as age-related increases in intraindividual variability and changes in EEG-oscillations are not considered. The present study compared averaged ERP peak and single trial time-frequency (TF) data analysis. METHODS Go/NoGo ERP waves amplitude/latency measures were compared with a TF analysis estimating single trial event-related EEG spectral power enhancement and intertrial phase-locking (ITC) in delta and theta band. RESULTS Age-related larger ITC was found for theta oscillations in the N2-P3 time range during NoGo, only. Discrepancies between N1/N2 ERP and TF results were obtained. Go/NoGo-P3 amplitude reductions in elderly were not related to an increased delta latency jitter. CONCLUSIONS Discrepancies between ERPs and TF results challenge conclusions made about age-related changes in Go/NoGo-N2. Earlier reports of age-related changes in P3 are supported by the present results. The study implies age-related impairments in a general neuronal inhibition mechanism and a specific response inhibition mechanism. SIGNIFICANCE The study indicates long-range communication impairments in the aged brain and the results are discussed considering hypotheses on increases in neural noise.

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.

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.

Age-related increases in within-person variability: delta and theta oscillations indicate that the elderly are not always old.

Behavioral and electrophysiological data related to performance in an auditory Go/NoGo task were analyzed in young and older adults in the present study. Especially, differences in within-person variability in behavior and neural activity between young and older adults and changes in topography of slow event-related oscillations (EROs) were of interest. Within-person variability in behavior was assessed by reaction time (RT) variability. Event-related delta and theta oscillations were analyzed using time-frequency transformation, which can give information on the time-course of single trial event-related EEG spectral power enhancement and intertrial phase-locking (ITC). In contrast to our previous visual Go/NoGo study, no under-recruitment of task-relevant brain regions was found for the auditory theta and delta EROs. Young did not differ from older adults in RT variability or in single trial delta/theta ITC. Altered recruitment of brain activity at advanced age was indicated, first, by stronger early theta phase-locking in older compared to young adults and, second, by a Go-specific lateralization of delta/theta activity. We conclude that within-person variability may increase with age, but the degree depends on performance level and the modality investigated.

Corpus callosum has different channels for transmission of spatial frequency information

Many studies suggest that separate retinocortical channels with different conduction speeds transmit the information about high and low spatial frequencies (SF). Similarly, separate callosal channels may be responsible for the transfer of different SFs. To test this hypothesis, interhemispheric transfer time (IHTT) was estimated using visual evoked potentials (VEPs) elicited by reversal of different SF checkerboard patterns, which were presented either in the right or left visual hemifield. VEPs were recorded from homologous occipital and parietal leads in 11 subjects. The P100 latencies obtained from directly stimulated hemispheres were defined as retinocortical conduction times. The difference in P100 latencies obtained from directly and indirectly stimulated hemispheres was defined as IHTT (i.e., contralateral P100 latency values subtracted from the ipsilateral latency values). The results, showing faster retinocortical transfer for low SF than for high SF, and the shortest transfer time at parietal leads only for low SF, indicate that the presented stimuli are transferred on separate retinocortical channels. Concerning the interhemispheric transfer (VEP-IHTT), faster right-to-left than left-to-right transfer for both low and high SF stimuli was found, which is in congruence with previous studies. Most important however, the VEP-IHTT was faster for low SF than high SF. These different interhemispheric transfer speeds support the hypothesis that transferring low SF, compared with high SF information, relies on larger callosal fibers. Thus, we conclude that indeed distinct callosal channels respond selectively to the SF content of visual stimuli.

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...

Frontal theta activity is pronounced during illusory perception

Object perception is driven by sensory information as well as expectations and prior experiences. The latter influence may increase when the sensory information is poor or inconclusive. Visual illusions, for example induced by ambiguous stimuli, provide a tool to investigate perceptual uncertainty, because ambiguous stimuli elicit switching between at least two perceptual alternatives. Theta oscillations may reflect the impact of visual illusion on perception since they are specifically important to coordinate information in large-scale brain networks, including visual sensory as well as higher-order brain areas. Theta responses elicited by an ambiguous and an unambiguous apparent motion-inducing stimulus were compared, thereby differentiating time periods of perceptual switching and perceptual stability (non-switching). The theta responses were larger at anterior than at posterior sites. This gradient was stronger during the ambiguous task than during the unambiguous task, even though sensory stimulation was comparable for both tasks. A transient increase of the theta response occurred during switching time periods for both the ambiguous and the unambiguous tasks, indicating that the theta response related to the perceptual switch might not be affected by the ambiguity of the stimulus. Irrespective of the percept switching or not, ambiguous stimuli elicited an enduring more prominent activation of higher-order rather than visual sensory brain areas. This indicates an increased reliance on expectations and prior information to ensure coherent object perception in particular when the visual information is degraded or elicits an ongoing conflict between perceptual interpretations.

Aging differentially affects alpha and beta sensorimotor rhythms in a go/nogo task

OBJECTIVES This study compared sensorimotor alpha and beta brain oscillations in young and older adults, to examine their functional distinctness and susceptibility to aging. METHODS Electroencephalographic data were compared between young (age 23±3) and older adults (age 64±7) in terms of event-related spectral perturbation in alpha and beta bands during a go/nogo task. RESULTS Age selectively influenced beta rhythms, with younger compared to older adults showing, first, less attenuation during movement preparation and execution, and, second, a greater rebound after movement end. Alpha rhythms differed after response inhibition, with an additional alpha rebound occurring in older, but not younger adults. CONCLUSION The results indicate neural over-recruitment in healthy aging, which appears most likely linked to alterations in multiple factors associated with sensory and cognitive aspects of motor control, and which does not consistently or directly impact response speed. SIGNIFICANCE The results imply that sensorimotor alpha and beta rhythms may reflect different neural trajectories in aging.