Attenuation of beta and gamma oscillations in schizophrenia spectrum patients following hand posture perturbation

Abnormal ERPs and Brain Dynamics Mediate Basic Self Disturbance in Schizophrenia: A Review of EEG and MEG Studies

Background: Interest in disordered sense of self in schizophrenia has recently re-emerged in the literature. It has been proposed that there is a basic self disturbance, underlying the diagnostic symptoms of schizophrenia, in which the person's sense of being a bounded individual continuous through time loses stability. This disturbance has been documented phenomenologically and at the level of cognitive tasks. However, the neural correlates of basic self disorder in schizophrenia are poorly understood. Methods: A search of PubMed was used to identify studies on self and schizophrenia that reported EEG or MEG data. Results: Thirty-three studies were identified, 32 using EEG and one using MEG. Their operationalizations of the self were divided into six paradigms: self-monitoring for errors, proprioception, self-other integration, self-referential processing, aberrant salience, and source monitoring. Participants with schizophrenia were less accurate on self-referential processing tasks and had slower response times across most studies. Event-related potential amplitudes differed across many early and late components, with reduced N100 suppression in source monitoring paradigms being the most replicated finding. Several studies found differences in one or more frequency band, but no coherent overall finding emerged in this area. Various other measures of brain dynamics also showed differences in single studies. Only some of the study designs were adequate to establish a causal relationship between the self and EEG or MEG measures. Conclusion: The broad range of changes suggests a global self disturbance at the neuronal level, possibly carried over from the resting state. Further studies that successfully isolate self-related effects are warranted to better understand the temporal-dynamic and spatial-topographic basis of self disorder and its relationship to basic self disturbance on the phenomenological level.

Neural Correlates of Schizotypal Personality Disorder: a Systematic Review of Neuroimaging and EEG Studies

BACKGROUND

Schizotypal personality disorder (SPD) is a cluster A personality disorder affecting 1.0% of general population, characterised by disturbances in cognition and reality testing dimensions, affect regulation, and interpersonal function. SPD shares similar but attenuated phenomenological, genetic, and neurobiological abnormalities with schizophrenia (SCZ) and is described as part of schizophrenia spectrum disorders.

OBJECTIVE

Aim of this work was to identify the major neural correlates of SPD.

METHODS

This is a systematic review conducted according to PRISMA statement. The protocol was prospectively registered in PROSPERO - International prospective register of systematic reviews. The review was performed to summarise the most comprehensive and updated evidence on functional neuroimaging and neurophysiology findings obtained through different techniques (DW-MRI, DTI, PET, SPECT, fMRI, MRS, EEG) in individuals with SPD.

RESULTS

Of the 52 studies included in this review, 9 were on DW-MRI and DTI, 11 were on PET and SPECT, 11 were on fMRI and MRS, and 21 were on EEG. It was complex to synthesise all the functional abnormalities found into a single, unified, pathogenetic pathway, but a common theme emerged: the dysfunction of brain circuits including striatal, frontal, temporal, limbic regions (and their networks) together with a dysregulation along the dopaminergic pathways.

CONCLUSION

Brain abnormalities in SPD are similar, but less marked, than those found in SCZ. Furthermore, different patterns of functional abnormalities in SPD and SCZ have been found, confirming the previous literature on the 'presence' of possible compensatory factors, protecting individuals with SPD from frank psychosis and providing diagnostic specificity.

Abnormalities of Alpha Activity in Frontocentral Region of the Brain as a Biomarker to Diagnose Adolescents With Bipolar Disorder

Objectives. To investigate brain abnormalities in adolescents with new-onset bipolar disorder (BD) during acute hypomanic and depressive episodes using electroencephalogram (EEG) analysis and to derive a computer-based method for diagnosis of the disorder. Methods. EEG spectral power and entropy of 21 adolescents with BD (included 11 patients in the hypomanic episode and 10 patients in the depressive episode) and 18 healthy adolescents were compared. Moreover, using significant differences and K-nearest-neighbors (KNN) classifier, it was attempted to distinguish the BD adolescents from normal ones. Results. The BD adolescents had higher values of spectral power in all frequency bands, particularly in the frontocentral, mid-temporal, and right parietal regions. Also, spectral entropy had significantly increased in delta, alpha, and gamma frequency bands for BD. A high accuracy of 95.8% was achieved by all significant differences in the alpha band in discriminating adolescents with BD. The depressive state showed higher values of spectral power and entropy in low-frequency bands (delta and theta) compared to the hypomanic state. Conclusion. Based on BD symptoms, especially inattention, increased alpha power is a rational finding which is associated with thalamus dysfunction. Thus, it seems that EEG alpha oscillation is the main source of abnormality in BD. Furthermore, EEG slowing in the depressive episode is related to inhibition of electrical activity and reduced cognitive functions.

The Importance of Sensory Processing in Mental Health: A Proposed Addition to the Research Domain Criteria (RDoC) and Suggestions for RDoC 2.0

The time is ripe to integrate burgeoning evidence of the important role of sensory and motor functioning in mental health within the National Institute of Mental Health's [NIMH] Research Domain Criteria [RDoC] framework (National Institute of Mental Health, n.d.a), a multi-dimensional method of characterizing mental functioning in health and disease across all neurobiological levels of analysis ranging from genetic to behavioral. As the importance of motor processing in psychopathology has been recognized (Bernard and Mittal, 2015; Garvey and Cuthbert, 2017; National Institute of Mental Health, 2019), here we focus on sensory processing. First, we review the current design of the RDoC matrix, noting sensory features missing despite their prevalence in multiple mental illnesses. We identify two missing classes of sensory symptoms that we widely define as (1) sensory processing, including sensory sensitivity and active sensing, and (2) domains of perceptual signaling, including interoception and proprioception, which are currently absent or underdeveloped in the perception construct of the cognitive systems domain. Then, we describe the neurobiological basis of these psychological constructs and examine why these sensory features are important for understanding psychopathology. Where appropriate, we examine links between sensory processing and the domains currently included in the RDoC matrix. Throughout, we emphasize how the addition of these sensory features to the RDoC matrix is important for understanding a range of mental health disorders. We conclude with the suggestion that a separate sensation and perception domain can enhance the current RDoC framework, while discussing what we see as important principles and promising directions for the future development and use of the RDoC.

A disembodied man: A case of somatopsychic depersonalization in schizotypal disorder

In the general concept of self-disturbances in schizophrenia and schizophrenia spectrum disorders, somatopsychic depersonalization (SPD) occupies a special place as it constitutes a syndrome that comprises feelings of detachment from one's own body and mental processes. However, apart from clinical descriptions, to date the pathophysiology of SPD is not fully understood due to the rareness of the syndrome and a lack of experimental studies. In a case study of one patient with schizotypal disorder, we applied a multimodal approach to understanding the SPD phenomena. The patient's clinical profile was identified as disruption of implicit bodily function, accompanied by depressive symptoms. On a neuropsychological level, the patient exhibited impairment in executive functioning, intact tactile perception and kinesthetic praxis. Behavioral tests revealed an altered sense of time but unimpaired self-agency. Furthermore, the patient exhibited a lack of empathy and he had autistic traits, although with a sufficient ability to verbalize his feelings. On the neurobiological level using an active and passive touch paradigm during functional magnetic resonance imaging (fMRI), we found a hyperconnectivity of the default-mode network and salience network and a hypoconnectivity of the central executive brain networks in the performance of the touch task as well as intact perceptual touch processing emerging from the direct comparisons of the touch conditions. Our data provide evidence for the important role of altered large-brain network functioning in SPD that corresponds to the specific behavioral and neurocognitive phenomena.

Self-disorder and brain processing of proprioception in schizophrenia spectrum patients: a re-analysis

BACKGROUND

Anomalies of self-awareness (self-disorders, SDs) are theorized to be basic to schizophrenia psychopathology. We have previously observed dysfunction of brain processing of proprioception in schizophrenia spectrum disorders (SZS). We hypothesized that SDs could be associated with abnormalities of early contralateral proprioceptive evoked oscillatory brain activity.

METHODS

We investigated the association between proprioceptive evoked potential components and SDs in a re-analysis of data from a subsample (n = 12) of SZS patients who had previously been observed with deviant proprioceptive evoked potentials and interviewed with the Examination of Anomalous Self-Experience (EASE) scale.

RESULTS

Higher EASE scores (i.e. increased SD) were associated with lower peak parietal gamma frequencies and higher peak beta amplitudes over frontal and parietal electrodes in the left hemisphere following right-hand proprioceptive stimulation.

CONCLUSION

Disorders of self-awareness may be associated with dysfunction of early phases of somatosensory processing. The findings are potentially relevant to our understanding of the pathophysiology of schizophrenia, but further studies are needed.

Sensory encoding in Neuregulin 1 mutants

Schizophrenic patients show altered sensory perception as well as changes in electrical and magnetic brain responses to sustained, frequency-modulated sensory stimulation. Both the amplitude and temporal precision of the neural responses differ in patients as compared to control subjects, and these changes are most pronounced for stimulation at gamma frequencies (20-40 Hz). In addition, patients display enhanced spontaneous gamma oscillations, which has been interpreted as 'neural noise' that may interfere with normal stimulus processing. To investigate electrophysiological markers of aberrant sensory processing in a model of schizophrenia, we recorded neuronal activity in primary somatosensory cortex of mice heterozygous for the schizophrenia susceptibility gene Neuregulin 1. Sensory responses to sustained 20-70 Hz whisker stimulation were analyzed with respect to firing rates, spike precision (phase locking) and gamma oscillations, and compared to baseline conditions. The mutants displayed elevated spontaneous firing rates, a reduced gain in sensory-evoked spiking and gamma activity, and reduced spike precision of 20-40 Hz responses. These findings present the first in vivo evidence of the linkage between a genetic marker and altered stimulus encoding, thus suggesting a novel electrophysiological endophenotype of schizophrenia.

High-frequency neural oscillations and visual processing deficits in schizophrenia

Visual information is fundamental to how we understand our environment, make predictions, and interact with others. Recent research has underscored the importance of visuo-perceptual dysfunctions for cognitive deficits and pathophysiological processes in schizophrenia. In the current paper, we review evidence for the relevance of high frequency (beta/gamma) oscillations towards visuo-perceptual dysfunctions in schizophrenia. In the first part of the paper, we examine the relationship between beta/gamma band oscillations and visual processing during normal brain functioning. We then summarize EEG/MEG-studies which demonstrate reduced amplitude and synchrony of high-frequency activity during visual stimulation in schizophrenia. In the final part of the paper, we identify neurobiological correlates as well as offer perspectives for future research to stimulate further inquiry into the role of high-frequency oscillations in visual processing impairments in the disorder.

A review of gamma oscillations in healthy subjects and in cognitive impairment

This review describes a wide range of functional correlates of gamma oscillations in whole-brain work, in neuroethology, sensory-cognitive dynamics, emotion, and cognitive impairment. This survey opens a new window towards understanding the brain's gamma activity. Gamma responses are selectively distributed in the whole brain, and do not reflect only a unique, specific function of the nervous system. Sensory responses from cortex, thalamus, hippocampus, and reticular formations in animal and human brains, and also cognitive responses, were described by several authors. According to reviewed results, it becomes obvious that cognitive disorders, and medication-which influence the transmitter release-change entirely the understanding of the big picture in cognitive processes. Gamma activity is evoked or induced by different sensory stimuli or cognitive tasks. Thus, it is argued that gamma-band synchronization is an elementary and fundamental process in whole-brain operation. In conclusion, reasoning and suggestions for understanding gamma activity are highlighted.

Closed eyes condition increases auditory brain responses in schizophrenia

The 40-Hz auditory steady-state responses (ASSRs) of 14 medicated schizophrenic patients were recorded in eyes-open and eyes-closed conditions as previously done in healthy volunteers. Patients show significantly increased precision of the evoked response with eyes closed, and a significant increase of broad-band noise activity when eyes are open.

Reduced natural oscillatory frequency of frontal thalamocortical circuits in schizophrenia

CONTEXT

Converging evidence from electrophysiological studies suggests that in individuals with schizophrenia, electroencephalographic frontal fast oscillations are reduced. It is still unclear whether this reduction reflects an intrinsic deficit of underlying cortical/thalamocortical circuits and whether this deficit is specific for frontal regions. Recent electrophysiological studies in healthy individuals have established that, when perturbed, different brain regions oscillate at a specific, intrinsically generated dominant frequency, the natural frequency.

OBJECTIVE

To assess the natural frequency of the posterior parietal, motor, premotor, and prefrontal cortices in patients with schizophrenia and healthy control subjects.

DESIGN

High-density electroencephalographic recordings during transcranial magnetic stimulation of 4 cortical areas were performed. Several transcranial magnetic stimulation–evoked electroencephalographic oscillation parameters, including synchronization, amplitude, and natural frequency, were compared across the schizophrenia and healthy control groups.

SETTING

Wisconsin Psychiatric Institute and Clinic, University of Wisconsin–Madison.

PARTICIPANTS

Twenty patients with schizophrenia and 20 age-matched healthy control subjects.

MAIN OUTCOME MEASURES

High-density electroencephalographic measurements of transcranial magnetic stimulation–evoked activity in 4 cortical areas, scores on the Positive and Negative Syndrome Scale, and performance scores (reaction time, accuracy) on 2 computerized tasks (word memory [Penn Word Recognition Test] and facial memory [Penn Facial Memory Test]).

RESULTS

Patients with schizophrenia showed a slowing in the natural frequency of the frontal/prefrontal regions compared with healthy control subjects (from an average of a 2-Hz decrease for the motor area to an almost 10-Hz decrease for the prefrontal cortex). The prefrontal natural frequency of individuals with schizophrenia was slower than in any healthy comparison subject and correlated with both positive Positive and Negative Syndrome Scale scores and reaction time on the Penn Word Recognition Test.

CONCLUSIONS

These findings suggest that patients with schizophrenia have an intrinsic slowing in the natural frequency of frontal cortical/thalamocortical circuits, that this slowing is not present in parietal areas, and that the prefrontal natural frequency can predict some of the symptoms as well as the cognitive dysfunctions of schizophrenia.

Gamma synchrony: towards a translational biomarker for the treatment-resistant symptoms of schizophrenia

The lack of efficacy for antipsychotics with respect to negative symptoms and cognitive deficits is a significant obstacle for the treatment of schizophrenia. Developing new drugs to target these symptoms requires appropriate neural biomarkers that can be investigated in model organisms, be used to track treatment response, and provide insight into pathophysiological disease mechanisms. A growing body of evidence indicates that neural oscillations in the gamma frequency range (30-80 Hz) are disturbed in schizophrenia. Gamma synchrony has been shown to mediate a host of sensory and cognitive functions, including perceptual encoding, selective attention, salience, and working memory - neurocognitive processes that are dysfunctional in schizophrenia and largely refractory to treatment. This review summarizes the current state of clinical literature with respect to gamma-band responses (GBRs) in schizophrenia, focusing on resting and auditory paradigms. Next, preclinical studies of schizophrenia that have investigated gamma-band activity are reviewed to gain insight into neural mechanisms associated with these deficits. We conclude that abnormalities in gamma synchrony are ubiquitous in schizophrenia and likely reflect an elevation in baseline cortical gamma synchrony ('noise') coupled with reduced stimulus-evoked GBRs ('signal'). Such a model likely reflects hippocampal and cortical dysfunction, as well as reduced glutamatergic signaling with downstream GABAergic deficits, but is probably less influenced by dopaminergic abnormalities implicated in schizophrenia. Finally, we propose that analogous signal-to-noise deficits in the flow of cortical information in preclinical models are useful targets for the development of new drugs that target the treatment-resistant symptoms of schizophrenia.