Dissociative symptoms and interregional EEG cross-correlations in paranoid schizophrenia.

Recent findings indicate that binding and synchronization of distributed activities are crucial for the mechanism of consciousness, and there is increased evidence that disruptions in feature binding produce disintegration of consciousness in schizophrenia. These data suggest that the disrupted binding and disintegration of consciousness could be related to dissociation, which is historically linked to Bleuler's concept of splitting in schizophrenia. In the present study we aimed to investigate relations among electroencephalogram (EEG) activities of cortical sites and used psychometric measures of positive and negative schizophrenia symptoms (Positive and Negative Syndrome Scale) and the Dissociative Experiences Scale (DES) in 58 patients with paranoid schizophrenia. The results show statistically significant Spearman correlations of the DES with cross-correlation function in nine (of 16) EEG pairs. Positive symptoms display significant Spearman correlation with mean of cross-correlation function in only one EEG pair (F4-C4). Results of the Mann-Whitney test between patients with higher (DES > or = 30) and lower dissociation show statistically significant differences between the groups for cross-correlations in nine EEG pairs. The results of this study provide the first supportive evidence for a negative relationship between cross-correlation indices and symptoms of dissociation in schizophrenia.

Sensitization, epileptic-like symptoms and local synchronization in patients with paranoid schizophrenia.

Recent findings indicate that changes in synchronization of neural activities underlying sensitization and kindling could be more comprehensively understood using nonlinear methods. With this aim we have examined local synchronization using novel measure of coarse-grained information rate (CIR) in 8 EEG signals recorded at different cortical areas in 44 patients with paranoid schizophrenia. The values of local synchronization that could reflect sensitization related changes in EEG activities of cortical sites were then related to psychometric measures of epileptic-like symptoms and positive and negative schizophrenia symptoms (PANSS). While no significant correlations between CIR and positive and negative symptoms have been found, statistically significant relationships described by Spearman correlation coefficients between CIR indices and results of LSCL-33 have been observed in 7 (of 8) EEG channels (r in the range from 0.307 to 0.374, p<0.05). Results of this study provide first supportive evidence for the relationship between local synchronization measured by CIR and epileptic-like symptoms in schizophrenia.

Chaos in schizophrenia associations, reality or metaphor?

There is evidence that schizophrenic associations display "chaotic", random-like behavior and decreased predictability. The evidence suggests a hypothesis that the "chaotic" mental disorganization could be explained within the concept of nonlinear dynamics and complexity in the brain that may cause chaotic neural organization. Testing of the hypothesis in the present study was performed using nonlinear analysis of bilateral electrodermal activity (EDA) during resting state and an association test in 56 schizophrenic patients and 44 healthy participants. EDA is a suitable measure of brain and autonomic activity reflecting neurobiological changes in schizophrenia that may indicate changes in nonlinear neural dynamics related to associative process. The results show that quantitative indices of chaotic dynamics (the largest Lyapunov exponents) calculated from EDA signals recorded during rest and the association test are significantly higher in schizophrenia patients than in the control group and increase during the test in comparison to the resting state. The difference was confirmed by statistical methods and using surrogate data testing that rejected an explanation within the linear statistical framework. The results provide supportive evidence that pseudo-randomness of schizophrenic associations and less predictability could be linked to increased complexity of nonlinear neural dynamics, although certain limitations in data interpretation must be taken into account.

EEG phase synchronization in patients with paranoid schizophrenia.

Recent findings suggest that specific deficits in neural synchrony and binding may underlie cognitive disturbances in schizophrenia and that key aspects of schizophrenia pathology involve discoordination and disconnection of distributed processes in multiple cortical areas associated with cognitive deficits. In the present study we aimed to investigate the underlying cortical mechanism of disturbed frontal-temporal-central-parietal connectivity in schizophrenia by examination of the synchronization patterns using wavelet phase synchronization index and coherence between all defined couples of 8 EEG signals recorded at different cortical sites in its relationship to positive and negative symptoms of schizophrenia. 31 adult schizophrenic outpatients with diagnosis of paranoid schizophrenia (mean age 27.4) were assessed in the study. The obtained results present the first quantitative evidence indicating direct relationship between wavelet phase synchronization and coherence in pairs of EEG signals recorded from frontal, temporal, central and parietal brain areas and positive and negative symptoms of schizophrenia. The performed analysis demonstrates that the level of phase synchronization and coherence in some pairs of EEG signals is inversely related to positive symptoms, negative symptoms and general psychopathology in temporal scales (frequency ranges) given by wavelet frequencies (WFs) equal to or higher than 7.56 Hz, and positively related to negative symptoms in wavelet frequencies equal to or lower than 5.35 Hz. This finding suggests that higher and lower frequencies may play a specific role in binding and connectivity and may be related to decreased or increased synchrony with specific manifestation in cognitive deficits of schizophrenia.

Dissociation, epileptic-like activity and lateralized electrodermal dysfunction in patients with schizophrenia and depression.

OBJECTIVES: Recent evidence indicates frequent EEG abnormalities in dissociated patients. This evidence is in agreement with findings that in certain psychiatric patients, psychosensory symptoms of epileptogenic nature, the so-called complex partial seizure-like symptoms occur. With respect to these findings, a hypothesis examined in this study states that increased level of experienced traumatic stress and dissociation in pathological conditions such as schizophrenia or depression relates to increased score of complex partial seizure-like symptoms. Also is suggested that the complex partial seizure-like symptoms might be related to unilateral hemispheric electrophysiological dysfunction, stress and dissociation. PARTICIPANTS AND METHODS: Psychometric assessment of dissociation, stress and measurement of right-left asymmetry of bilateral EDA in patients with schizophrenia (N=34) and depression (N=41) in comparison to healthy controls (N=36). RESULTS: Results indicate that increased traumatic stress and dissociation in both groups of patients significantly relate to increased level of complex partial seizure-like symptoms, and may cause the right-left EDA asymmetry. CONCLUSIONS: The data suggest relationship between left-hemispheric asymmetry and sympathetic over-activation in schizophrenia, and between right-hemispheric asymmetry with sympathetic under-activation in depression.

Neural complexity, dissociation and schizophrenia.

BACKGROUND: Recent findings confirm, following Bleuler's and Janet's tradition, the significant influence of stress-related events and dissociation in the pathogenesis of schizophrenia. Dissociative reaction is most often a consequence of traumatic experiences that lead to a loss of inhibitory control and may produce split fragments of the mind. Recent findings in studies on brain complexity and neural synchronization suggest the hypothesis that the specific functional fragmentation of neural subsystems could be linked to the dissociation and splitting in schizophrenia that may be reflected in dynamic neural complexity and assessed by measures reflecting these processes. MATERIAL/METHODS: In this context, the hypothesis tested in this study is that dynamic changes in electrodermal activity (EDA) as a measure of brain and autonomic activity could serve as an indicator of specific changes in neural complexity in schizophrenia patients. Therefore, bilateral EDA under rest conditions in 30 schizophrenic patients and 30 healthy subjects was measured. RESULTS: The results of nonlinear and statistical analysis of EDA records indicated increased neural complexity indexed by a point-wise correlation dimension (PD2) in schizophrenia patients compared with healthy controls. CONCLUSIONS: This result represents preliminary support for the hypothesis that increased neural complexity reflects the functional fragmentation of neural subsystems related to traumatic dissociation and splitting in schizophrenia.

Lateralized electrodermal dysfunction and complexity in patients with schizophrenia and depression.

OBJECTIVE: Recent evidence indicates that in psychiatric patients with schizophrenia and depression, lateralized EDA changes linked to temporal-limbic electrophysiological dysfunction occur. These clinical findings provide evidence for brain asymmetry and disruptions related to integrative brain activity in pathological conditions. METHODS: These changes in brain asymmetry may be assessed by linear analysis of EDA measurement and nonlinear analysis of brain complexity calculated as information entropy. Two groups of patients with established diagnosis of paranoid schizophrenia (N=35), unipolar depression (N=35) and a control group of 35 healthy controls were examined by measurement of bilateral electrodermal activity (EDA). In non-linear data analysis of the EDA time series in resting state the method of recurrence quantification analysis was applied. RESULTS: In these patients significant right-left EDA asymmetry and asymmetry of information entropy calculated by non-linear recurrence quantification analysis of EDA records have been found. Similar asymmetry has not been observed in the group of healthy controls. CONCLUSIONS: Because information entropy reflects the complexity of the deterministic structure in the system, then unilaterally increased entropy in patients with schizophrenia and depression likely indicates specific nonlinear disturbances in limbic circuits that modulate EDA. These data are in accordance with recent findings that indicate apparent differences in nonlinear neural patterns in the psychiatric diseases and nonlinear behavior of healthy brain.

Traumatic dissociation, epileptic-like phenomena, and schizophrenia.

OBJECTIVES: According to recent evidence, trauma and stress are important etiological factors in pathogenesis of schizophrenia. However, the hypothetical influence of traumatic stress on epileptic-like (or kindling) phenomena in schizophrenia is at this time unclear. METHODS: In order to discover the influence of trauma, 82 patients with a diagnosis of paranoid schizophrenia and 50 healthy controls were assessed for symptoms of dissociation, traumatic stress and psycho-sensory symptoms of epileptic origin. RESULTS: We have found significant traumatization and dissociation in patients who met the cut-off score for psychosensory epileptic-like symptoms and also significant correlations among these measures have been found. CONCLUSIONS: These data suggest a certain role of epileptic-like phenomena in dissociative states in schizophrenia and are in accordance with rare intracranial EEG findings which suggest a certain role of epileptiform events in schizophrenia.