The predictive value of P300-amplitudes in the course of schizophrenic disorders

Evidence-based medicine and electrophysiology in schizophrenia

In research on schizophrenia electrophysiological measures have been investigated to identify biomarkers of the disorder, indices enabling differential diagnosis among psychotic disorders, prognostic indicators or endophenotypes. The present systematic review will focus on the most largely studied electrophysiological indices, i.e., qualitative or quantitative (limited to spectral analysis) EEG and the P300 event-related potential. The PubMed clinical query was used with research methodology filters for each of the following categories: diagnosis/prognosis/ aetiology and a broad sensitive search strategy. The key-words: SCHIZOPHRENIA AND EEG/P3/P300 were used. The search results were then narrowed by including the terms "human" and "English language", and cross-referenced. Systematic reviews and meta-analyses, when available, were also used for cross-referencing. Case reports and studies irrelevant to the topics and methodologies under examination were excluded. The remaining papers were screened to verify the eligibility for this systematic review. Inclusion criteria were: a) a diagnosis of schizophrenia confirmed by DSM-III/ICD-9 criteria (or later editions of the same classification systems); b) the inclusion of both a schizophrenia study group and an healthy control group (when appropriate, i.e., for P300 and quantitative EEG); c) qualitative or spectral EEG findings and amplitude measures for P300. The included studies were then reviewed to verify homogeneity of the results, as well as the presence of the information needed for the present systematic review and meta-analysis. Previous reviews and studies meeting the above requirements (n = 22 for qualitative EEG; n = 45 for spectral EEG and n = 132 for P300) were classified according to the Oxford Centre for Evidence-based Medicine (EBM) levels of evidence criteria. For qualitative EEG as a diagnostic test, the majority of studies predated the introduction of DSM-III and were excluded from the review. Few post DSM-III studies investigated the usefulness of qualitative EEG in the differential diagnosis between schizophrenia and psychosis due to general medical condition. None of them was Oxford CEBM level 3b (non-consecutive-study or cohort-study without consistently-applied reference standard) or better (exploratory or validating cohort-study). No meta-analysis could be conducted due to the lack of reliable quantification methods in the reviewed studies. For spectral EEG as a diagnostic test, most studies qualified as level 4 (case-control study with poor reference standard), and only 24% as level 3b or better. An increase of slow activity in patients is reported by most of these studies. As to meta-analyses examining 29 studies, with 32 independent samples for the delta band and 35 for the theta band, a moderate effect size was found and only 1 study yielded findings in the opposite direction for both measures. There was no identified source for the discrepancy. The analysis of moderator factors included medication, band frequency limits, spectral parameters and disease stage. The medication status was significant for the theta band but the effect was unclear as findings for drug-naïve and drug-free patients were in a different direction. Chronicity had a significant effect on both delta and theta bands, with slow activity increase larger in chronic than in first episode patients. For P3 amplitude reduction as a diagnostic index, 63% of the studies qualified as level 3b or better. Meta-analysis (52 studies, 60 independent samples) results demonstrated a large effect size. None of the studies reported opposite findings. The analysis of moderator factors, including medication status and disease stage, revealed no significant effect on data heterogeneity. In conclusion, the examined indices are good candidates but are not ready yet for clinical applications aimed to improve present diagnostic standards for schizophrenia. Further research carried out according to adequate methodological standards and based on large scale multi-center studies is mandatory.

Annotation: what electrical brain activity tells us about brain function that other techniques cannot tell us - a child psychiatric perspective

BACKGROUND

Monitoring brain processes in real time requires genuine subsecond resolution to follow the typical timing and frequency of neural events. Non-invasive recordings of electric (EEG/ERP) and magnetic (MEG) fields provide this time resolution. They directly measure neural activations associated with a wide variety of brain states and processes, even during sleep or in infants. Mapping and source estimation can localise these time-varying activation patterns inside the brain.

METHODS

Recent EEG/ERP research on brain functions in the domains of attention and executive functioning, perception, memory, language, emotion and motor processing in ADHD, autism, childhood-onset schizophrenia, Tourette syndrome, specific language disorder and developmental dyslexia, anxiety, obsessive-compulsive disorder, and depression is reviewed.

RESULTS

Over the past two decades, electrophysiology has substantially contributed to the understanding of brain functions during normal development, and psychiatric conditions of children and adolescents. Its time resolution has been important to measure covert processes, and to distinguish cause and effect.

CONCLUSIONS

In the future, EEG/ERP parameters will increasingly characterise the interplay of neural states and information processing. They are particularly promising tools for multilevel investigations of etiological pathways and potential predictors of clinical treatment response.

No effects of l-dopa and bromocriptine on psychophysiological parameters of human selective attention

Patients with schizophrenia exhibit diverse cognitive deficits, one of which is a loss of the ability to focus attention. According to the revised dopamine hypothesis of schizophrenia both an increased mesolimbic and a decreased prefrontal dopaminergic activity is suggested to be involved in schizophrenia. The current study was designed to explore the relationship between dopamine and two psychophysiological parameters of selective attention, i.e. P300 amplitude and processing negativity (PN) in healthy volunteers. In two separate experiments, with a double-blind, balanced and placebo-controlled crossover design, 18 healthy male volunteers were orally administered either 300 mg l-dopa (precursor of dopamine) or placebo (experiment I), or 1.25mg bromocriptine (D2 agonist) or placebo (experiment II). Following this treatment they were tested in an auditory, dichotic selective attention paradigm. An increase in P300 amplitude was found following deviant stimuli when compared to standard stimuli and following attended stimuli when compared to unattended stimuli, regardless of treatment. Similarly, PN was found regardless of treatment. Neither l-dopa nor bromocriptine affected task performance or the amplitudes of PN or P300. In the present study neither l-dopa nor bromocriptine affected PN, P300 amplitude or task performance in healthy controls, phenomena which are usually found to be disrupted in schizophrenia. This indicates that P300 amplitude and PN are neither affected by a global (l-dopa) increased dopaminergic activity, nor by a more selectively towards striatal areas targeted (bromocriptine) increase in dopaminergic activity.

The Wisconsin Card Sort Test and P300 responses to novel auditory stimuli in schizophrenic patients

The authors studied the relationship between performance on the Wisconsin Card Sort Test (WCST) and P300 activity in schizophrenics and normal controls. Fourteen male predominantly medicated schizophrenics and matched non-ill controls were administered the WCST and tests of temporal lobe (delayed verbal and spatial memory) and general intellectual functioning (Shipley). Patients were rated with negative and positive symptom scales extracted from the Brief Psychiatric Rating Scale. Subjects performed a tone discrimination task requiring identification of rare targets in both a standard oddball paradigm and a three-stimulus paradigm that included rare novel sounds. Reference independent data from 16 scalp electrodes yielded Global Field Power (GFP), from which P300 latency was determined. P300 amplitude measures included amplitude at this identified latency as well as amplitude integrated over a 100 ms time window centered over it. These amplitude measures were examined at six selected electrode locations. Schizophrenics produced smaller P300 responses that tended to be slower, but there were no group differences in the relationships between neuropsychological performance and P300 responses. Across diagnostic groups percent perseverative errors predicted lower integrated and peak P300 amplitude during the novel but not the standard oddball paradigm. The effect on integrated P300 amplitude was localized to anterior leads after novel stimuli. Negative symptoms predicted lower WCST performance, lower integrated P300 amplitude, and smaller GFP after novel stimuli. Positive symptoms predicted reduced overall GFP and specific but inconsistent reductions in parietal P300 amplitude. The results suggest relationships between dorsolateral prefrontal competence, P300 activity in response to stimulus novelty, and negative symptoms in schizophrenic patients, paralleling findings obtained from blood flow and other measures of brain activity.

Sensory gating deficits during the mid-latency phase of information processing in medicated schizophrenia patients

Sensory gating during preattentive phases of information processing has been extensively examined. Sensory gating processes that occur during subsequent phases of information processing have not been fully examined. The relationship between P50 sensory gating and schizophrenia symptoms remains underspecified and the clinical correlates of N100 and P200 gating are yet to be examined. Sensory gating indices derived from the mid-latency auditory evoked responses during preattentive (P50) and attentive (N100, P200) phases of information processing were collected from schizophrenia patients who were stable and mainly being treated with atypical antipsychotic medications (n=23) and age- and gender-matched healthy control subjects (n=23). Schizophrenia patients had demonstrable habituation or sensory gating difficulties throughout the mid-latency range of information processing. Moreover, we found no correlations between P50-derived sensory gating indices and the amplitude or latency of the more attention-related P300 evoked response. A number of N100 and P200 gating measures correlated with P300 variables. Finally, we found no correlations between sensory gating indices and schizophrenia symptoms clusters. These results suggest that sensory gating is a pervasive abnormality in schizophrenia patients that is not limited to the preattentive phase of information processing. Furthermore, the data suggest that N100 and P200 gating indices may influence subsequent information processing.

Meta-analysis of P300 and schizophrenia: patients, paradigms, and practical implications

The goal of the present meta-analysis was to identify factors that contribute to P300 event-related brain potential (ERP) differences in patients with schizophrenia compared to unaffected controls in an attempt to characterize the clinically relevant dimensions underlying P300 deficits in patients with schizophrenia. P300 effect size (d) was smaller in amplitude and longer in latency in schizophrenic patients compared to normal controls, with the strongest effects obtained from the auditory oddball. Paranoid subtype demonstrated larger P300 amplitude effect sizes than other disease subtypes, and P300 latency effect size decreased with disease duration. Psychopathology severity and antipsychotic medications were unrelated to P300 amplitude effect size. Gender proportion, educational level, and stimulus and task variables also affected P300 amplitude and latency effect sizes. The findings are used to formulate a theoretical account of the empirical data and provide suggestions for maximizing the utility of the P300 component in the assessment of schizophrenia.

Rightward cerebral asymmetry in subtypes of schizophrenia according to Leonhard's classification and to DSM-IV: a structural MRI study

Although well documented, brain structural abnormalities in schizophrenia are non-specific, and morphometric parameters show significant overlap between patients and healthy controls. Such inconsistencies in neuroimaging findings could represent different levels of severity along a single pathogenic process or distinct clinical and etiopathological psychoses within a schizophrenic spectrum. The aim of the present study was the investigation of distinct brain abnormalities in different subtypes of schizophrenia. Forty patients were classified according to DSM-IV and Leonhard's classifications. Psychopathology was assessed by the Positive and Negative Syndrome Scale (PANSS) and the Negative Symptom Rating Scale (NSRS). Patients were compared to 20 healthy volunteers on volumetric measures of cerebral structures (hemisphere, hippocampus and planum temporale) and ventricular-brain ratio (VBR) obtained by magnetic resonance imaging. Patients showed rightward asymmetry of cerebral hemispheres and increased VBR. Rightward asymmetry correlated with severity of negative symptoms and prevailed in the systematic forms of Leonhard, suggesting a distinct pattern of left hemisphere abnormality in this subgroup of psychoses. Increased VBR values showed a single normal distribution in the subgroups, indicating that ventricular enlargement is not restricted to a subgroup but is present to a certain degree in all cases.

P300 subcomponents and clinical symptoms in schizophrenia

A small P300 component of the auditory event-related potential has been found to predict poor clinical outcome with a higher amount of thought disorders in schizophrenia and has been proposed as a marker for an underlying neurodevelopmental disorder with prominent thought disorders, early age of onset, prominent negative symptoms and positive family history. The present study was designed to confirm our previous findings with subcomponent analysis. Using dipole source analysis a temporo-basal (TB) P300 as well as a temporo-superior (TS) P300 and LP potential were separated. Fifty patients with schizophrenia (DSM-IV) were included in the study. Late auditory event-related P300 potentials were recorded to infrequent auditory stimuli after treatment psychopathology and family history were assessed. The TB-P300 amplitudes were significantly negatively correlated with thought disorders remaining after treatment and were positively correlated with age of onset. Illness duration was significantly correlated to TB-P300 and TS-P300 amplitudes in the group of patients with late onset. No significant correlations were found with negative symptoms. Family history did not show significant effects on P300. A smaller P300 in patients with more thought disorder remaining after stabilization on medication and an earlier age of onset support the hypothesis that P300 characterizes schizophrenic patients with an underlying neurodevelopmental disorder with specific clinical symptom clusters. On the other hand, diminished P300 with illness duration in the group of patients with later age of onset supports an underlying neurodegenerative progressive process in this subgroup of patients.

The neurophysiological meaning of auditory P300 in subtypes of schizophrenia

Event-related potentials are a powerful tool to investigate the real-time course of brain electrical mass activation during cognitive processing. In several psychiatric disorders, differences compared to healthy subjects have been reliably described. The specificity and the pathophysiological meaning of the findings were unclear in most studies, however. This review summarizes methodological aspects and findings, in healthy subjects and psychiatric patients, of investigations based on the auditory oddball paradigm, which evokes the P300 component of event-related potentials. Recent convergent results from P300 and brain imaging studies allowed the interpretation of P300 findings in psychotic disorders in terms of different specific and meaningful neurophysiological disturbances. Namely, core schizophrenia is characterized by a left-temporal dysfunction associated with deficits in verbal processing. Acute remitting schizophrenia-like psychoses (cycloid psychosis, ICD-10 F23), on the other hand, show normal hemispheric balance but consistent signs of cerebral hyperarousal. Recent studies further indicate that the drive for action of manic patients does not rely on over-excitation but rather on frontal disinhibition. The findings may help to further advance the understandings and sub-grouping of functional psychoses based on pathophysiological mechanisms.

Anxiety as a primary symptom in cycloid psychosis

Psychotic anxiety has not been systematically included in standard psychopathologic and diagnostic literature, presumably because anxiety is implicitly perceived to be an emphatically comprehensible consequence of the cognitive symptoms of psychosis. This review gives an overview of neurophysiologic studies that indicate different pathogenic mechanisms for different types of psychosis. Convergent and complementary structural and functional imaging findings, biochemical and neuropsychological data allow conjecture as to neurophysiologic-psychopathologic links in cycloid psychosis. Intriguing results suggest that in cycloid psychosis, a generalized hyperasousal related to the tonus of the noradrenergic system may be the basic disturbance causing the delusionary and perceptual psychotic distortions. The findings are specific for cycloid psychoses, which are diagnosed as polymorphous psychosis in the International Classification of Diseases and Related Health Problems, 10th Edition. Furthermore, these findings are consistent with the author's hypothesis that the emotional derailment is the primary disturbance in cycloid psychosis (anxiety-elation). In contrast, cognitive disturbances are secondary and remit after the exceptional emotional state is rebalanced.

Basic symptoms and P300 abnormalities in young schizophrenic patients

Among the reasons for the relatively limited number of investigations of self-knowledge phenomena should be included, in addition to theoretical motives, the difficulties regarding the use of instruments available for this kind of approach and their content validity. This study investigates the relationship between subjective and objective deficits in schizophrenia, taking into account subjective experiences of cognitive impairment, clinical symptoms, and cognitive evoked potentials (P300 component). A group of 36 young schizophrenic patients (29 on neuroleptic treatment and seven drug-naive) were considered, together with a comparison group of 36 healthy subjects. Auditory event-correlated potentials (ERPs) were obtained using a simple "oddball" paradigm. Clinical symptoms were rated with the Brief Psychiatric Rating Scale (BPRS) and Scales for the Assessment of Positive and Negative Symptoms (SAPS and SANS), and while subjective disturbances were assessed by the Frankfurter Beschwerde Fragebogen (FBF, also called the Complaint Questionnaire). Correlation analysis showed that P300 amplitude was inversely correlated with subjective experiences of cognitive deficit, especially in the area of automatic skills and overstimulation. No relationship emerged between BPRS, SANS, and SAPS scores and P300 alterations. The results suggest that subjective cognitive disturbances, more than objective symptoms, are related to P300 alterations in schizophrenia, and that the FBF questionnaire appropriately covers the domain of schizophrenic cognitive disorders.

Distinct neurophysiological mechanisms for manic and cycloid psychoses: evidence from a P300 study on manic patients

Pathologically asymmetrical P300 fields with right lateralized peaks were described in core schizophrenia as an expression of left-temporal functional deficits, while higher than normal amplitudes were found in cycloid psychosis. This latter finding appeared to be specific for cycloid psychosis and was explained by a generalized cerebral hyperarousal. Based on some psychopathological analogies with cycloid psychosis, and on the comparable pharmacological treatment of the acute episodes, a group of 19 manic patients was investigated immediately after remission and clinical stabilization of an episode. Patients with psychotic features were excluded to avoid overlaps with cycloid psychosis. Patients showed normal P300 amplitudes and no pathological asymmetries of the field, but more posterior positive areas compared to age- and sex-matched controls. This indicates that the neurophysiological changes underlying mania are different from both core schizophrenia and cycloid psychosis. Based on previous three-dimensional source location studies, this finding indicates that disinhibition due to reduced frontal lobe activity, and not hyperarousal, is the basic functional mechanism of manic disorders.