An initial report of a new biological marker for bipolar disorder: P85 evoked brain potential

Lifetime and point prevalence of psychotic symptoms in adults with bipolar disorders: a systematic review and meta-analysis

Psychotic symptoms, that we defined as delusions or hallucinations, are common in bipolar disorders (BD). This systematic review and meta-analysis aims to synthesise the literature on both lifetime and point prevalence rates of psychotic symptoms across different BD subtypes, including both BD type I (BDI) and BD type II (BDII). We performed a systematic search of Medline, PsycINFO, Embase and Cochrane Library until 5 August 2021. Fifty-four studies (N = 23 461) of adults with BD met the predefined inclusion criteria for evaluating lifetime prevalence, and 24 studies (N = 6480) for evaluating point prevalence. Quality assessment and assessment of publication bias were performed. Prevalence rates were calculated using random effects meta-analysis, here expressed as percentages with a 95% confidence interval (CI). In studies of at least moderate quality, the pooled lifetime prevalence of psychotic symptoms in BDI was 63% (95% CI 57.5-68) and 22% (95% CI 14-33) in BDII. For BDI inpatients, the pooled lifetime prevalence was 71% (95% CI 61-79). There were no studies of community samples or inpatient BDII. The pooled point prevalence of psychotic symptoms in BDI was 54% (95 CI 41-67). The point prevalence was 57% (95% CI 47-66) in manic episodes and 13% (95% CI 7-23.5) in depressive episodes. There were not enough studies in BDII, BDI depression, mixed episodes and outpatient BDI. The pooled prevalence of psychotic symptoms in BDI may be higher than previously reported. More studies are needed for depressive and mixed episodes and community samples.Prospero registration number: CRD 42017052706.

Genetic Determinants of Gating Functions: Do We Get Closer to Understanding Schizophrenia Etiopathogenesis?

Deficits in the gating of sensory stimuli, i.e., the ability to suppress the processing of irrelevant sensory input, are considered to play an important role in the pathogenesis of several neuropsychiatric disorders, in particular schizophrenia. Gating is disrupted both in schizophrenia patients and their unaffected relatives, suggesting that gating deficit may represent a biomarker associated with a genetic liability to the disorder. To assess the strength of the evidence for the etiopathogenetic links between genetic variation, gating efficiency, and schizophrenia, we carried out a systematic review of human genetic association studies of sensory gating (suppression of the P50 component of the auditory event-related brain potential) and sensorimotor gating (prepulse inhibition of the acoustic startle response). Sixty-three full-text articles met the eligibility criteria for inclusion in the review. In total, 117 genetic variants were reported to be associated with gating functions: 33 variants for sensory gating, 80 variants for sensorimotor gating, and four variants for both sensory and sensorimotor gating. However, only five of these associations (four for prepulse inhibition-CHRNA3 rs1317286, COMT rs4680, HTR2A rs6311, and TCF4 rs9960767, and one for P50 suppression-CHRNA7 rs67158670) were consistently replicated in independent samples. Although these variants and genes were all implicated in schizophrenia in research studies, only two polymorphisms (HTR2A rs6311 and TCF4 rs9960767) were also reported to be associated with schizophrenia at a meta-analytic or genome-wide level of evidence. Thus, although gating is widely considered as an important endophenotype of schizophrenia, these findings demonstrate that evidence for a common genetic etiology of impaired gating functions and schizophrenia is yet unsatisfactory, warranting further studies in this field.

Meta-analysis of auditory P50 sensory gating in schizophrenia and bipolar disorder

The ability of the brain to reduce the amount of trivial or redundant sensory inputs is called gating function. Dysfunction of sensory gating may lead to cognitive fragmentation and poor real-world functioning. The auditory dual-click paradigm is a pertinent neurophysiological measure of sensory gating function. This meta-analysis aimed to examine the subcomponents of abnormal P50 waveforms in bipolar disorder and schizophrenia to assess P50 sensory gating deficits and examine effects of diagnoses, illness states (first-episode psychosis vs. schizophrenia, remission vs. episodes in bipolar disorder), and treatment status (medication-free vs. medicated). Literature search of PubMed between Jan 1st 1980 and March 31st 2019 identified 2091 records for schizophrenia, 362 for bipolar disorder. 115 studies in schizophrenia (4932 patients), 16 in bipolar disorder (975 patients) and 10 in first-degree relatives (848 subjects) met the inclusion criteria. P50 sensory gating ratio (S2/S1) and S1-S2 difference were significantly altered in schizophrenia, bipolar disorder and their first-degree relatives. First-episode psychosis did not differ from schizophrenia, however episodes altered P50 sensory gating in bipolar disorder. Medications improve P50 sensory gating alterations in schizophrenia significantly and at trend level in bipolar disorder. Future studies should examine longitudinal course of P50 sensory gating in schizophrenia and bipolar disorder.

Augmenting pharmacotherapy with neuromodulation techniques for the treatment of bipolar disorder: a focus on the effects of mood stabilizers on cortical excitability

Introduction: Mood stabilizers and antipsychotics have been demonstrated to be effective in Bipolar Disorder, with lithium as the gold standard. However, the presence of adverse events and treatment-resistance is still a relevant issue. To this respect, the use of brain stimulation techniques may be considered as an augmentation strategy, with both Transcranial Magnetic Stimulation (TMS) and Transcranial Direct Current Stimulation (tDCS) having shown some level of efficacy in bipolar patients although clinical trials are still not sufficient to draw any conclusion. Areas covered: The authors have conducted a systematic review of the literature, in order to evaluate the role of mood stabilizers on neural activity and cortical excitability. Furthermore, the article reviews neuromodulation techniques and highlights the potential of integrating pharmacological first-line therapies with these techniques to treat BD patients. Expert opinion: The combination of neuromodulation techniques and available pharmacotherapies is a valuable opportunity which is not undermined by specific effects on cortical excitability and could improve BD patient outcome. Neurostimulation techniques may be considered safer than antidepressant treatments in BD, with a lower level of manic switches and may represent a new treatment strategy in BD depressive episodes.

Auditory sensory gating in patients with bipolar disorders: A meta-analysis

BACKGROUND

Sensory gating (SG) refers to the attenuation of neural response to the second identical stimulus and is conceptualized as an automatic process to inhibit redundant information. Although its deficit in schizophrenia has been well-documented, the degree to which SG is modulated by bipolar disorders (BD) remains elusive. Thus, the present meta-analysis study aimed to explore the pooled effect sizes of SG ability in BD patients.

METHODS

Ten studies consisting of 14 individual investigations were included, consisting of 699 healthy controls and 568 BD patients. The effect sizes, calculated as Cohen's d, were estimated individually for S2/S1 ratio and S1-S2 difference. Additionally, S2/S1 ratio was examined in two conditions: BD with and without a history of psychosis.

RESULTS

We found that BD patients with (d=0.847, p<0.001) or without (d=0.589, p<0.001) a psychotic history exhibited an impaired SG ability compared to the healthy controls. Furthermore, both S1-S2 difference score and S2/S1 ratio, at a group level, can differentiate BD patients from healthy controls.

LIMITATIONS

We were not able to divide patients with BD into different subtypes, and thus our data should be interpreted with cautions.

CONCLUSION

These findings suggest BD itself impairs SG ability, which worsens with a psychotic history. The current understanding invites future research to ascertain the role of SG in subtypes of BD.

Biological aspects and candidate biomarkers for psychotic bipolar disorder: A systematic review

AIM

We carried out a systematic review of the available literature about potential biomarkers of psychotic bipolar disorder (BD-P), a specific subset presenting worse outcome and greater risk of relapse than non-psychotic bipolar disorder (BD-NP).

METHODS

We searched the main psychiatric databases (PubMed, ISI Web of Knowledge, PsychInfo). Only original articles with the main topic of BD-P compared to schizophrenia/BD-NP/healthy controls (HC) written in English from 1994 to 2015 were included.

RESULTS

BD-P patients presented higher kynurenic acid levels in the cerebrospinal fluid, elevated anti- S accharomyces cerevisiae antibodies levels, and lower serum levels of dehydroepiandrosterone sulfate and progesterone than BD-NP/HC. Event-related potentials abnormalities have been identified in BD-P with respect to BD-NP. BD-P patients also presented bigger ventricles but similar hippocampal volumes compared to BD-NP/HC. Although the results are contrasting, some cognitive deficits seemed to be related to the psychotic dimension of bipolar affective disorder, such as impairment in verbal/logical memory, working memory, verbal and semantic fluency and executive functioning. Finally, polymorphisms of genes, such as NRG1, 5HTTLPR (s), COMT, DAOA and some chromosome regions (16p12 and 13q), were positively associated with BD-P.

CONCLUSION

Data about the identification of specific biomarkers for BD-P are promising, but most of them have not yet been replicated. They could lead the clinicians to an early diagnosis and proper treatment, thus ameliorating outcome of BD-P and reducing the biological changes associated with a long duration of illness. Further studies with bigger samples are needed to detect more specific biological markers of the psychotic dimension of bipolar affective disorder.

Auditory M50 and M100 sensory gating deficits in bipolar disorder: a MEG study

OBJECTIVES

Auditory sensory gating deficits have been reported in subjects with bipolar disorder, but the hemispheric and neuronal origins of this deficit are not well understood. Moreover, gating of the auditory evoked components reflecting early attentive stage of information processing has not been investigated in bipolar disorder. The objectives of this study were to investigate the right and left hemispheric auditory sensory gating of the M50 (preattentive processing) and M100 (early attentive processing) in patients diagnosed with bipolar I disorder by utilizing magnetoencephalography (MEG).

METHODS

Whole-head MEG data were acquired during the standard paired-click paradigm in 20 bipolar I disorder patients and 20 healthy controls. The M50 and the M100 responses were investigated, and dipole source localizations were also investigated. Sensory gating were determined by measuring the strength of the M50 and the M100 response to the second click divided by that of the first click (S2/S1).

RESULTS

In every subject, M50 and M100 dipolar sources localized to the left and right posterior portion of superior temporal gyrus (STG). Bipolar I disorder patients showed bilateral gating deficits in M50 and M100. The bilateral M50 S2 source strengths were significantly higher in the bipolar I disorder group compared to the control group.

LIMITATIONS

The sample size was relatively small. More studies with larger sample sizes are warranted. Bipolar subjects were taking a wide range of medications that could not be readily controlled for.

CONCLUSIONS

These findings suggest that bipolar I disorder patients have auditory gating deficits at both pre-attentive and early attentive levels, which might be related to STG structural abnormality.

Family history of psychosis moderates early auditory cortical response abnormalities in non-psychotic bipolar disorder

OBJECTIVES

Bipolar I disorder is a disabling illness affecting 1% of people worldwide. Family and twin studies suggest that psychotic bipolar disorder (BDP) represents a homogeneous subgroup with an etiology distinct from non-psychotic bipolar disorder (BDNP) and partially shared with schizophrenia. Studies of auditory electrophysiology [e.g., paired-stimulus and oddball measured with electroencephalography (EEG)] consistently report deviations in psychotic groups (schizophrenia, BDP), yet such studies comparing BDP and BDNP are sparse and, in some cases, conflicting. Auditory EEG responses are significantly reduced in unaffected relatives of psychosis patients, suggesting that they may relate to both psychosis liability and expression.

METHODS

While 64-sensor EEGs were recorded, age- and gender-matched samples of 70 BDP, 35 BDNP {20 with a family history of psychosis [BDNP(+)]}, and 70 psychiatrically healthy subjects were presented with typical auditory paired-stimuli and auditory oddball paradigms.

RESULTS

Oddball P3b reductions were present and indistinguishable across all patient groups. P2s to paired stimuli were abnormal only in BDP and BDNP(+). Conversely, N1 reductions to stimuli in both paradigms and P3a reductions were present in both BDP and BDNP(-) groups but were absent in BDNP(+).

CONCLUSIONS

Although nearly all auditory neural response components studied were abnormal in BDP, BDNP abnormalities at early- and mid-latencies were moderated by family psychosis history. The relationship between psychosis expression, heritable psychosis risk, and neurophysiology within bipolar disorder, therefore, may be complex. Consideration of such clinical disease heterogeneity may be important for future investigations of the pathophysiology of major psychiatric disturbance.

P50 sensory gating is a trait marker of the bipolar spectrum

Sensory gating deficit, assessed by a paired auditory stimulus paradigm (P50), has been reported as a stable marker of schizophrenia. The aim of this study was to explore if this neurophysiological disturbance also fulfilled stability criteria in the bipolar disorder (BD) spectrum bipolar, as state independence is one of the main points to be considered as a potential endophenotype of the illness. The P50 evoked potential was studied in 95 healthy controls and 126 bipolar euthymic patients. Euthymia was established according to Van Gorp's criteria. Bipolar I and II subtypes were analyzed separately. The influence of a lifetime history of psychoses was also evaluated in the clinical sample. P50 gating was deficitary in all the subsamples of patients relative to healthy comparison subjects. Bipolar I patients with and without a history of psychosis showed higher P50 ratios than the other subgroups of patients, although these differences were not significant. P50 alterations were mainly due to a deficit in the inhibition of the second wave (test wave or S2) amplitude.

CONCLUSIONS

The findings suggest that this inhibitory deficit can be considered characteristic of the illness and that the intensity of the gating abnormality varies according to the severity of BD.

Gating of a novel brain potential is associated with perceptual anomalies in bipolar disorder

OBJECTIVES

Our laboratory recently identified the P85 gating ratio as a candidate biomarker for bipolar disorder. In order to evaluate the phenomenological significance of P85 gating, the current study examined reports of perceptual anomalies and their relationship to the P50 and P85 physiological measures of sensory gating.

METHODS

Reports of perceptual anomalies on the Structured Clinical Interview to Assess Perceptual Anomalies were compared in patients meeting DSM-IV criteria for paranoid schizophrenia (n = 66), schizoaffective disorder (n = 45), or bipolar I disorder (n = 42), and controls (n = 56), as well as their relationship with P85 and P50 gating.

RESULTS

The bipolar disorder group reported significantly more auditory, visual, and total anomalies than both the schizophrenia and control groups. The schizophrenia group also had more anomalies than the control group. Comparison of psychiatric subgroups revealed that the bipolar depressed, bipolar disorder with psychosis, and schizoaffective bipolar type groups reported the most anomalies compared to the other patient groups (bipolar disorder without psychosis, schizoaffective, bipolar manic). The total perceptual anomalies score and the P85 ratio significantly differentiated the bipolar disorder, schizoaffective, and paranoid schizophrenia groups from each other.

CONCLUSIONS

These findings provide evidence of the phenomenological significance of P85. The results also yield further support not only for the P85 ratio, but also for increased reports of perceptual anomalies as possible markers for bipolar disorder.

Brain oscillations in bipolar disorder in search of new biomarkers

This report presents six cardinal results obtained with methods of oscillatory brain dynamics in euthymic and manic bipolar patients in comparison to healthy controls. Measurements include changes in oscillatory response activities in the theta, alpha, beta, and gamma frequency ranges. The analysis shows that spontaneous and response activities in the alpha range are highly reduced in euthymic and manic patients, respectively; conversely, beta responses are increased in euthymic and manic patients. Lithium use seems to be associated with further and significant increase in the beta frequency range in euthymic patients. Theta responses to auditory target stimulus during odd-ball paradigm appeared in two different frequency bands (4-6 and 6-8 Hz) in healthy participants. However, only fast theta responses were highly reduced under cognitive load in drug-free euthymic patients. The analysis of connectivity was performed by assessment of long-distance coherence function in the gamma frequency range. Both manic and euthymic patients presented significantly decreased fronto-temporal coherence function during visual odd-ball task, indicating a selective reduction in connectivity during cognitive processing. The present report also discusses that these six oscillatory parameters may serve as an ensemble of biomarkers for diagnostic purposes and tracking treatment response in bipolar disorder.

Different patterns of auditory information processing deficits in chronic schizophrenia and bipolar disorder with psychotic features

With the development of DSM-V and ICD-11 the definitions of psychiatric disorders are under re-evaluation. The emphasis is shifted from distinct disorders to clusters defined not only by symptomatology, but also by underlying neurobiology and cognitive deficits. Bipolar disorder I (BD-I) and schizophrenia (SZ) are of special interest since their differential diagnosis is often problematic and they partially overlap in measures ranging from genetics to neurophysiology. Event-related potentials (ERPs) are one of the most studied factors but the results are still controversial, primarily in BD-I, where ERPs reflecting different stages of auditory information processing have been much less investigated. In this study, we aimed at investigating the changes of five auditory event-related potentials (P50 and N100 suppression, duration and pitch deviant mismatch negativity (MMN) and P3b) in 20 SZ and 20 BD-I patients with a history of psychosis and 21 healthy control subjects. Our data revealed substantial differences between the two patient groups. Only patients with SZ demonstrated impaired N100 suppression, shorter duration deviant MMN latency and attenuated P3b amplitude, while prolonged pitch deviant MMN latency was found to be characteristic of the BD-I group. No shared ERP abnormalities were observed among the patient groups. Our results indicate that SZ and BD-I are characterized by highly different neurophysiological profiles when measured in the same laboratory setting.

Differentiation between bipolar disorder and schizophrenia revealed by neural oscillation to speech sounds: an MEG study

OBJECTIVES

  Psychiatrists have long debated whether bipolar disorder (BP) and schizophrenia (SZ) are the clinical outcomes of discrete or shared causative processes. SZ shows significantly delayed peak latencies of the evoked neural oscillation (eNO) power and reduced eNO power to speech sounds in the left hemisphere in comparison to normal controls (NC), suggesting deficits in the fast mechanism for identifying speech sounds for SZ. The current study tested the hypothesis that the eNO to speech sounds could be differentiated between BP and SZ patients.

METHODS

  The magnetoencephalographic data of 11 BP, 12 SZ, and 15 NC subjects were evaluated, and we analyzed the eNO power and phase-locking in 20-45 Hz to speech sounds and pure tones in the left hemisphere.

RESULTS

  The major findings were that: (i) BP subjects exhibited larger eNO power to speech sounds compared to NC and SZ; (ii) SZ subjects showed delayed eNO and phase-locking to speech sounds specifically in the left hemisphere; and (iii) no significant differences were observed in the response to pure tones among the three groups.

CONCLUSIONS

  The present study showed that different patterns in eNO to speech sounds are present in BP, SZ, and NC subjects. The eNO to speech sounds in the left hemisphere is a potential index to distinguish BP and SZ.