Oscillatory Activities in Multiple Frequency Bands in Patients with Schizophrenia During Motion Perception.

Patients with schizophrenia show impairment in binding stimulus features into coherent objects, which are reflected in disturbed oscillatory activities. This study aimed to identify disturbances in multiple oscillatory bands during perceptual organization of motion perception in patients with schizophrenia. EEG was recorded from healthy controls and patients with schizophrenia during continuous presentation of a motion stimulus which induces reversals between two exogenously generated perceptions. This stimulus was used to investigate differences in motion binding processes between healthy controls and patients with schizophrenia. EEG signals were transformed into frequency components by means of the Morlet wavelet transformation in order to analyse inter-trial coherences (ITC) in the delta (1-4 Hz), theta (4-7 Hz), alpha (8-12 Hz), and gamma (28-48 Hz) frequency bands during exogenous motion binding. Patients showed decreased delta-ITC in occipital and theta-ITC in central and parietal areas, while no significant differences were found for neither alpha nor gamma-ITCs. The present study provides one of the first insights on the oscillatory synchronizations related with the motion perception in schizophrenia. The ITC differences revealed alterations in the consistency of large-scale integration and transfer functions in patients with schizophrenia.

What does the broken brain say to the neuroscientist? Oscillations and connectivity in schizophrenia, Alzheimer's disease, and bipolar disorder.

The application of the concept and methods of brain oscillations has been an important research area in neurosciences. In the last decades, besides the application in cognitive processes, the study of changes in brain oscillations in diseases has also become an important focal point of research. In the present paper, some remarkable examples in three different diseases are taken into consideration: 1) schizophrenia (SZ), 2) Alzheimer's disease (AD), 3) bipolar disorders (BD). In the current literature, decreased oscillations in cortical recordings are observed in most of the pathologies. For example, decrease of gamma activity in SZ, decrease of delta activity in almost all diseases, as well as frequency shifts in alpha and the lower frequencies were recorded. However, there are also paradoxical cases in which an increase of oscillatory activities is observed. In BD, whereas alpha activity is greatly decreased, a huge increase of beta activity is observed. Or, in SZ, a paradoxical increase of gamma activity can be observed during cognitive loading. We also observed paradoxical changes in the analysis of connectivity. In AD, we find that alpha, delta, and theta coherences between distant parts of the cortex are greatly decreased, whereas in the gamma band, event-related coherences attain very high values. The comparison of the results and paradoxical changes in diseases may lead to important conclusions related to the web of oscillations and neurotransmitters. In turn, we could gain new insights to approach "brain function", in general.

New rather than old? For working memory tasks with abstract patterns the P3 and the single-trial delta response are larger for modified than identical probe stimuli.

Memory-guided decision making is dynamic and context-dependent, even though many studies describe an enhancement of the P3 for recognized items in memory tasks ("old-new effect"). This study utilized a delay-dependent working memory task during which decision making could be optimized by focusing attention on detected changes instead of recognized similarities. Mean P3 amplitude and delta activity were analyzed from participants who classified probe stimuli as identical or modified. The P3 amplitudes were larger for modified than for identical probes, even when the probe occurred 4,000 ms after the primary stimulus. Enhanced single-trial amplitude, trial-by-trial consistency, and frontoparietal phase coherence of delta activity contributed to the larger P3 for the modified probe. Thus, context-dependent attentional resource allocation supporting memory-guided decisions might explain the enhancement of the P3 for specific probe types.

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.

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.