Association between electroencephalographic modulation, psychotic-like experiences and cognitive performance in the general population

AIM

An association between deficit of electroencephalographic (EEG) modulation during an odd-ball task and psychotic symptoms has been described in clinical samples, in agreement with the proposed role for altered salience in psychosis. To discard the possible influence of medication, the relationship between psychotic-like experiences and EEG modulation in the general population was explored.

METHODS

EEG and psychotic-like experiences were assessed in 194 healthy subjects during a P300 paradigm. EEG modulation was assessed as changes from pre-stimulus to response windows in spectral entropy (SE, a measurement of signal irregularity), median frequency (MF, a quantifier of the frequency distribution of oscillatory activity) and theta, alpha, beta-1, beta-2 and gamma relative power (RP, a summary of the distribution of spectral components).

RESULTS

A significant widespread decrease in SE and MF from baseline to response was found, with a significant increase in RP for theta and a decrease for higher frequency bands, supporting an increase in EEG regularity and a slowing of brain oscillations during the response. Furthermore, a significant association was found between SE modulation and distress of negative psychotic-like experiences, as well as between verbal memory and RP modulation for beta-1. Performance in verbal fluency was associated with the increase in theta RP during the response.

CONCLUSION

EEG irregularity of healthy subjects decreased at the expense of a larger contribution of theta RP and a decreased contribution of fast frequency bands. Subjects with smaller modulation showed poorer cognitive scores and greater distress of negative psychotic-like experiences.

Noise power associated with decreased task-induced variability of brain electrical activity in schizophrenia

In schizophrenia, both increased baseline metabolic and electroencephalographic (EEG) activities as well as decreased task-related modulation of neural dynamics have been reported. Noise power (NP) can measure the background EEG activity during task performance, and Shannon entropy (SE) is useful for quantifying the global modulation of EEG activity with a high temporal resolution. In this study, we have assessed the possible relationship between increased NP in theta and gamma bands and decreased SE modulation in 24 patients with schizophrenia and 26 controls over the parietal and central regions during a P300 task. SE modulation was calculated as the change from baseline to the active epoch (i.e., 150-550 ms following the target stimulus onset). Patients with schizophrenia displayed statistically significant higher NP values and lower SE modulation than healthy controls. We found a significant association between gamma NP and SE in all of the participants. Specifically, a NP increase in the gamma band was followed by a decrease in SE change. These results support the notion that an excess of gamma activity, unlocked to the task being performed, is accompanied by a decreased modulation of EEG activity in schizophrenia.

[Relationship between subclinical psychotic symptoms and cognitive performance in the general population]

INTRODUCTION

Subclinical psychotic symptoms are associated to negative life outcomes in the general population, but their relationship with cognitive performance is still not well understood. Assessing the relationship between performance in cognitive domains and subclinical psychotic symptoms in the general population may also help understand the handicap attributed to clinical psychosis, in which these alterations are present.

METHODS

Subclinical and cognitive assessments were obtained in 203 participants from the general population by means of the Community Assessment of Psychic Experiences, the Brief Assessment of Cognition in Schizophrenia, the Wechsler Adults Intelligence Scale and the Wisconsin Card Sorting Test. The positive and negative subclinical symptoms and their relationship with age and cognition were examined, followed by assessing the influence of subclinical depression scores on the possible relationships between those subclinical psychotic symptoms and cognitive deficits.

RESULTS

Inverse relationships were found between frequency in the Community Assessment of Psychic Experiences positive dimension and motor speed, and frequency and distress in the Community Assessment of Psychic Experiences negative dimension and motor speed. A direct relationship was also found between distress scores of the positive dimension and executive functions. Both positive and negative subclinical symptoms were related to depression scores.

CONCLUSIONS

Psychotic symptoms, similar to those in the clinical population, may be associated with cognitive deficits in the general population.

Gamma power and cognition in patients with schizophrenia and their first-degree relatives

BACKGROUND

Gamma oscillations are essential for functional neural assembly formation underlying higher cerebral functions. Previous studies concerning gamma band power in schizophrenia have yielded diverse results.

METHODS

In this study, we assessed gamma band power in minimally treated patients with schizophrenia, their first-degree relatives and healthy controls during an oddball paradigm performance, as well as the relation between gamma power and cognitive performance.

RESULTS

We found a higher gamma power in the patient group than in the healthy controls at the P3, P4, Fz, Pz and T5 sites. Compared with their relatives, gamma power in the patients was only marginally higher over P3 and P4. We found a nearly significant inverse association between gamma power at F4 and Tower of London performance in the patients, as well as a significant inverse association between gamma power at T5 and verbal memory and working memory scores in the relatives.

CONCLUSION

These results support higher total gamma power in association with schizophrenia and its inverse association with cognitive performance in patients and their first-degree relatives.

A comparative study of event-related coupling patterns during an auditory oddball task in schizophrenia

OBJECTIVE

The aim of this research is to explore the coupling patterns of brain dynamics during an auditory oddball task in schizophrenia (SCH).

APPROACH

Event-related electroencephalographic (ERP) activity was recorded from 20 SCH patients and 20 healthy controls. The coupling changes between auditory response and pre-stimulus baseline were calculated in conventional EEG frequency bands (theta, alpha, beta-1, beta-2 and gamma), using three coupling measures: coherence, phase-locking value and Euclidean distance.

MAIN RESULTS

Our results showed a statistically significant increase from baseline to response in theta coupling and a statistically significant decrease in beta-2 coupling in controls. No statistically significant changes were observed in SCH patients.

SIGNIFICANCE

Our findings support the aberrant salience hypothesis, since SCH patients failed to change their coupling dynamics between stimulus response and baseline when performing an auditory cognitive task. This result may reflect an impaired communication among neural areas, which may be related to abnormal cognitive functions.

Structural correlates of cognitive deficit and elevated gamma noise power in schizophrenia

AIMS

The aim of this study was to assess the relation between cognition, gray matter (GM) volumes and gamma noise power (amount of background oscillatory activity in the gamma band) in schizophrenia.

METHODS

We explored the relation between cognitive performance and regional GM volumes using voxel-based morphometry (VBM), in order to discover if the association between gamma noise power (an electroencephalography measurement of background activity in the gamma band) and cognition is observed through structural deficits related to the disease. Noise power, magnetic resonance imaging and cognitive assessments were obtained in 17 drug-free paranoid patients with schizophrenia and 13 healthy controls.

RESULTS

In comparison with controls, patients showed GM deficits at posterior cingulate (bilateral),left inferior parietal (supramarginal gyrus) and left inferior dorsolateral prefrontal regions. Patients exhibited a direct association between performance in working memory and right temporal (superior and inferior gyri) GM densities. They also displayed a negative association between right anterior cerebellum volume and gamma noise power at the frontal midline (Fz) site.

CONCLUSION

A structural deficit in the cerebellum may be involved in gamma activity disorganization in schizophrenia. Temporal structural deficits may relate to cognitive dysfunction in this illness.

Cognitive outcome and gamma noise power unrelated to neuregulin 1 and 3 variation in schizophrenia

BACKGROUND

Neuregulins are a family of signalling proteins that orchestrate a broad range of cellular responses. Four genes encoding Neuregulins 1-4 have been identified so far in vertebrates. Among them, Neuregulin 1 and Neuregulin 3 have been reported to contribute to an increased risk for developing schizophrenia. We hypothesized that three specific variants of these genes (rs6994992 and rs3924999 for Neuregulin 1 and rs10748842 for Neuregulin 3) that have been related to this illness may modify information processing capacity in the cortex, which would be reflected in electrophysiological parameters (P3b amplitude or gamma noise power) and/or cognitive performance.

METHODS

We obtained DNA from 31 patients with schizophrenia and 23 healthy controls and analyzed NRG1 rs6994992, NRG1 rs3924999 and NRG3 rs10748842 promoter polymorphisms by allelic discrimination with real-time polymerase chain reaction (PCR). We compared cognitive outcome, P300 amplitude parameters and an electroencephalographic measure of noise power in the gamma band between the groups dichotomized according to genotype.

RESULTS

Contrary to our hypothesis, we could not detect any significant influence of variation in Neuregulin 1/Neuregulin 3 polymorphisms on cognitive performance or electrophysiological parameters of patients with schizophrenia.

CONCLUSIONS

Despite our findings, we cannot discard that other genetic variants and, more likely, interactions between those variants and with genetic variation related to different pathways may still influence cerebral processing in schizophrenia.

Spatial distribution and cognitive correlates of gamma noise power in schizophrenia

BACKGROUND

Brain activity is less organized in patients with schizophrenia than in healthy controls (HC). Noise power (scalp-recorded electroencephalographic activity unlocked to stimuli) may be of use for studying this disorganization. Method Fifty-four patients with schizophrenia (29 minimally treated and 25 stable treated), 23 first-degree relatives and 27 HC underwent clinical and cognitive assessments and an electroencephalographic recording during an oddball P300 paradigm to calculate noise power magnitude in the gamma band. We used a principal component analysis (PCA) to determine the factor structure of gamma noise power values across electrodes and the clinical and cognitive correlates of the resulting factors.

RESULTS

The PCA revealed three noise power factors, roughly corresponding to the default mode network (DMN), frontal and occipital regions respectively. Patients showed higher gamma noise power loadings in the first factor when compared to HC and first-degree relatives. In the patients, frontal gamma noise factor scores related significantly and inversely to working memory and problem-solving performance. There were no associations with symptoms.

CONCLUSIONS

There is an elevated gamma activity unrelated to task processing over regions coherent with the DMN topography in patients with schizophrenia. The same type of gamma activity over frontal regions is inversely related to performance in tasks with high involvement in these frontal areas. The idea of gamma noise as a possible biological marker for schizophrenia seems promising. Gamma noise might be of use in the study of underlying neurophysiological mechanisms involved in this disease.

Limbic hyperactivity associated to verbal memory deficit in schizophrenia

In schizophrenia there seems to be an inefficient activation of prefrontal and hippocampal regions. Patients tend to show worse cognitive performance in functions subserved by those regions as compared to healthy controls in spite of higher regional activation. However, the association between activation abnormalities and cognitive deficits remains without being understood. In the present study, we compared cerebral perfusion using single-photon emission tomography (SPECT) in patients and controls to study the association between activation patterns and cognitive performance in this disease. The SPECT studies were simultaneously obtained with an electrophysiological recording during a P300 paradigm to elicit P3a and P3b components. We included 23 stable patients with paranoid schizophrenia and 29 healthy controls that underwent clinical and cognitive assessments. Patients with schizophrenia showed an increased perfusion in the right hippocampus with respect to healthy controls, they also displayed a statistically significant inverse association between perfusion in the left hippocampus and verbal memory performance. Healthy controls showed an inverse association between perfusion in the left dorsolateral prefrontal (DLPFC) region and working memory performance. P3b but not P3a amplitude was significantly lower in patients. The limbic overactivation in the patients may contribute to their cognitive deficits in verbal memory.

Elevated noise power in gamma band related to negative symptoms and memory deficit in schizophrenia

BACKGROUND

There is an increasing consideration for a disorganized cerebral activity in schizophrenia, perhaps relating to a synaptic inhibitory deficit in the illness. Noise power (scalp-recorded electroencephalographic activity unlocked to stimuli) may offer a non-invasive window to assess this possibility.

METHODS

29 minimally-treated patients with schizophrenia (of which 17 were first episodes) and 27 healthy controls underwent clinical and cognitive assessments and an electroencephalographic recording during a P300 paradigm to calculate signal-to-noise ratio and noise power magnitudes in the theta and gamma bands.

RESULTS

In comparison to controls, a significantly higher gamma noise power was common to minimally-treated and first episode patients over P3, P4, T5 and Fz electrode sites. Those high values were directly correlated to negative symptom severity and inversely correlated to verbal memory scores in the patients. There were no differences in signal-to-noise ratio magnitudes among the groups. Gamma noise power at Fz discriminated significantly between patients and controls. No significant differences were found in theta noise power or in gamma noise power over the other electrode sites between the groups of patients and controls.

LIMITATIONS

We have not assessed phase-locked and non-phase locked power changes, a complementary approach that may yield useful information.

CONCLUSIONS

Gamma noise power may represent a useful and non-invasive tool for studying brain dysfunction in psychotic illness. These results suggest an inefficient activation pattern in schizophrenia.

Effects of a bacteriocin-like inhibitory substance from Carnobacterium piscicola against human and salmon isolates of Listeria monocytogenes

The aim of this study was to characterize the antagonism of a bacteriocin-like inhibitory substance (BLIS) produced by Carnobacterium piscicola L103 against Listeria monocytogenes strains isolated from salmon and human samples. The inhibitory effect of the BLIS was evaluated in Tryptic soy agar (TSA) during different growth phases of L. monocytogenes at 5 degrees C, using the well diffusion method. Also, the type of inhibition, either bacteriostatic or bactericidal of the BLIS in Tryptic soy broth (TSB), was studied and the development of resistant cells investigated. Results showed an antagonistic effect of the BLIS on all the strains of L. monocytogenes. Four selected strains presented a higher sensitivity to the BLIS in the exponential growth phase and were more resistant in the stationary phase. In TSB, the inhibitory substance showed a partially bactericidal effect on L. monocytogenes. After inactivation of the BLIS with a protease, however, a regrowth of L. monocytogenes was found. The isolate most affected by the action of the BLIS was one of salmon origin. From the 86 isolated colonies that grew in the presence of the BLIS, 93% showed total resistance and 7% partial resistance, which was maintained through five consecutive culture cycles in the absence of the BLIS.