Evidence of abnormalities in mid-latency auditory evoked responses (MLAER) in cognitive subtypes of patients with schizophrenia

Early and middle latency auditory event-related potentials do not explain differences in neuropsychological performance between schizophrenia spectrum patients and matched healthy controls

Abnormalities of early and middle latency auditory event-related potentials (ERPs) are widespread in schizophrenia and have been suggested to be associated with cognitive deficits in schizophrenia patients. In this cross-sectional study with schizophrenia patients (n=30) and psychiatrically healthy counterparts (n=31) (matched for age, sex, education), we investigated whether auditory information processing (measured via amplitudes and gating of the auditory ERPs P50, N100 and P200) correlates with neuropsychological performance across cognitive domains. The groups differed significantly in amplitudes and gating of N100 and P200 potentials as well as in neuropsychological performance, but not in P50 amplitude and gating. Neither amplitudes nor gating of auditory ERPs correlated with neuropsychological performance. Neuropsychological intergroup differences could not be explained by abnormalities in auditory information processing. Although pronounced impairments exist on the levels of both auditory information processing and cognitive performance in schizophrenia, these abnormalities are not directly associated with each other.

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.

P50, N100, and P200 Auditory Sensory Gating Deficits in Schizophrenia Patients

BACKGROUND

Sensory gating describes neurological processes of filtering out redundant or unnecessary stimuli during information processing, and sensory gating deficits may contribute to the symptoms of schizophrenia. Among the three components of auditory event-related potentials reflecting sensory gating, P50 implies pre-attentional filtering of sensory information and N100/P200 reflects attention triggering and allocation processes. Although diminished P50 gating has been extensively documented in patients with schizophrenia, previous studies on N100 were inconclusive, and P200 has been rarely examined. This study aimed to investigate whether patients with schizophrenia have P50, N100, and P200 gating deficits compared with control subjects.

METHODS

Control subjects and clinically stable schizophrenia patients were recruited. The mid-latency auditory evoked responses, comprising P50, N100, and P200, were measured using the auditory-paired click paradigm without manipulation of attention. Sensory gating parameters included S1 amplitude, S2 amplitude, amplitude difference (S1-S2), and gating ratio (S2/S1). We also evaluated schizophrenia patients with PANSS to be correlated with sensory gating indices.

RESULTS

One hundred four patients and 102 control subjects were examined. Compared to the control group, schizophrenia patients had significant sensory gating deficits in P50, N100, and P200, reflected by larger gating ratios and smaller amplitude differences. Further analysis revealed that the S2 amplitude of P50 was larger, while the S1 amplitude of N100/P200 was smaller, in schizophrenia patients than in the controls. We found no correlations between sensory gating indices and schizophrenia positive or negative symptom clusters. However, we found a negative correlation between the P200 S2 amplitude and Bell's emotional discomfort factor/Wallwork's depressed factor.

CONCLUSION

Till date, this study has the largest sample size to analyze P50, N100, and P200 collectively by adopting the passive auditory paired-click paradigm without distractors. With covariates controlled for possible confounds, such as age, education, smoking amount and retained pairs, we found that schizophrenia patients had significant sensory gating deficits in P50-N100-P200. The schizophrenia patients had demonstrated a unique pattern of sensory gating deficits, including repetition suppression deficits in P50 and stimulus registration deficits in N100/200. These results suggest that sensory gating is a pervasive cognitive abnormality in schizophrenia patients that is not limited to the pre-attentive phase of information processing. Since P200 exhibited a large effect size and did not require additional time during recruitment, future studies of P50-N100-P200 collectively are highly recommended.

Sensory Gating Deficits in First-Episode Psychosis: Evidence From Neurophysiology, Psychophysiology, and Neuropsychology

Sensory gating deficits are commonly found in patients with schizophrenia. However, there is still scarce research on this issue. Thirty-eight patients with first-episode psychosis (FEP) were compared to thirty-eight controls. A condition-test paradigm of event-related potentials (ERP), prepulse inhibition (PPI), and some specific tasks of the MATRICS Consensus Cognitive Battery (MCCB) were used (i.e., TMT, BACS-SC, and Fluency for processing speed and CPT-IP for attention and vigilance). The ERP components measured were P50, N1, and P2. The PPI intervals examined were 30, 60, and 120 msec. Regarding the MCCB, processing speed and attention/vigilance cognitive domains were selected. FEP patients showed significant deficits in N1 and P2 components, at 30 and 60 PPI levels and in all the MCCB subtests selected. We obtained significant relationships in N1 with PPI-60, and with one MCCB subtest for processing speed. In addition, this same subtest showed significant association with P2. Therefore, sensory gating functioning is widely impaired since the very early stages of schizophrenia.

The mGluR2 positive allosteric modulator, SAR218645, improves memory and attention deficits in translational models of cognitive symptoms associated with schizophrenia

Normalization of altered glutamate neurotransmission through activation of the mGluR2 has emerged as a new approach to treat schizophrenia. These studies describe a potent brain penetrant mGluR2 positive allosteric modulator (PAM), SAR218645. The compound behaves as a selective PAM of mGluR2 in recombinant and native receptor expression systems, increasing the affinity of glutamate at mGluR2 as inferred by competition and GTPγ³⁵S binding assays. SAR218645 augmented the mGluR2-mediated response to glutamate in a rat recombinant mGluR2 forced-coupled Ca²⁺ mobilization assay. SAR218645 potentiated mGluR2 agonist-induced contralateral turning. When SAR218645 was tested in models of the positive symptoms of schizophrenia, it reduced head twitch behavior induced by DOI, but it failed to inhibit conditioned avoidance and hyperactivity using pharmacological and transgenic models. Results from experiments in models of the cognitive symptoms associated with schizophrenia showed that SAR218645 improved MK-801-induced episodic memory deficits in rats and attenuated working memory impairment in NMDA Nr1^neo-/- mice. The drug reversed disrupted latent inhibition and auditory-evoked potential in mice and rats, respectively, two endophenotypes of schizophrenia. This profile positions SAR218645 as a promising candidate for the treatment of cognitive symptoms of patients with schizophrenia, in particular those with abnormal attention and sensory gating abilities.

Schizophrenia: the role of sleep and circadian rhythms in regulating dopamine and psychosis

Schizophrenia has long been associated with abnormalities in circadian rhythms and sleep. Up until now, there have been no thorough reviews of the potential mechanisms behind the myriad of circadian and sleep abnormalities observed in schizophrenia and psychosis. We present evidence of sleep playing an important role in psychosis predominantly mediated by dopaminergic pathways. A synthesis of both human and animal experimental work suggests that the interplay between sleep and dopamine is important in the generation and maintenance of psychosis. In particular, both animal and human data point to sleep disruption increasing dopamine release and sensitivity. Furthermore, elevated dopamine levels disrupt sleep and circadian rhythms. The synthesis of knowledge suggests that circadian rhythms, dopamine dysregulation, and psychosis are intricately linked. This suggests that treatment of circadian disturbance may be a useful target in improving the lives and symptoms of patients with schizophrenia.

Modulation of mGlu2 Receptors, but Not PDE10A Inhibition Normalizes Pharmacologically-Induced Deviance in Auditory Evoked Potentials and Oscillations in Conscious Rats

Improvement of cognitive impairments represents a high medical need in the development of new antipsychotics. Aberrant EEG gamma oscillations and reductions in the P1/N1 complex peak amplitude of the auditory evoked potential (AEP) are neurophysiological biomarkers for schizophrenia that indicate disruption in sensory information processing. Inhibition of phosphodiesterase (i.e. PDE10A) and activation of metabotropic glutamate receptor (mGluR2) signaling are believed to provide antipsychotic efficacy in schizophrenia, but it is unclear whether this occurs with cognition-enhancing potential. The present study used the auditory paired click paradigm in passive awake Sprague Dawley rats to 1) model disruption of AEP waveforms and oscillations as observed in schizophrenia by peripheral administration of amphetamine and the N-methyl-D-aspartate (NMDA) antagonist phencyclidine (PCP); 2) confirm the potential of the antipsychotics risperidone and olanzapine to attenuate these disruptions; 3) evaluate the potential of mGluR2 agonist LY404039 and PDE10 inhibitor PQ-10 to improve AEP deficits in both the amphetamine and PCP models. PCP and amphetamine disrupted auditory information processing to the first click, associated with suppression of the P1/N1 complex peak amplitude, and increased cortical gamma oscillations. Risperidone and olanzapine normalized PCP and amphetamine-induced abnormalities in AEP waveforms and aberrant gamma/alpha oscillations, respectively. LY404039 increased P1/N1 complex peak amplitudes and potently attenuated the disruptive effects of both PCP and amphetamine on AEPs amplitudes and oscillations. However, PQ-10 failed to show such effect in either models. These outcomes indicate that modulation of the mGluR2 results in effective restoration of abnormalities in AEP components in two widely used animal models of psychosis, whereas PDE10A inhibition does not.

Knockout of NMDA receptors in parvalbumin interneurons recreates autism-like phenotypes

Autism is a disabling neurodevelopmental disorder characterized by social deficits, language impairment, and repetitive behaviors with few effective treatments. New evidence suggests that autism has reliable electrophysiological endophenotypes and that these measures may be caused by n-methyl-d-aspartic acid receptor (NMDAR) disruption on parvalbumin (PV)-containing interneurons. These findings could be used to create new translational biomarkers. Recent developments have allowed for cell-type selective knockout of NMDARs in order to examine the perturbations caused by disrupting specific circuits. This study examines several electrophysiological and behavioral measures disrupted in autism using a PV-selective reduction in NMDA R1 subunit. Mouse electroencephalograph (EEG) was recorded in response to auditory stimuli. Event-related potential (ERP) component amplitude and latency analysis, social testing, and premating ultrasonic vocalizations (USVs) recordings were performed. Correlations were examined between the ERP latency and behavioral measures. The N1 ERP latency was delayed, sociability was reduced, and mating USVs were impaired in PV-selective NMDA Receptor 1 Knockout (NR1 KO) as compared with wild-type mice. There was a significant correlation between N1 latency and sociability but not between N1 latency and premating USV power or T-maze performance. The increases in N1 latency, impaired sociability, and reduced vocalizations in PV-selective NR1 KO mice mimic similar changes found in autism. Electrophysiological changes correlate to reduced sociability, indicating that the local circuit mechanisms controlling N1 latency may be utilized in social function. Therefore, we propose that behavioral and electrophysiological alterations in PV-selective NR1 KO mice may serve as a useful model for therapeutic development in autism. Autism Res 2013, 6: 69-77. © 2013 International Society for Autism Research, Wiley Periodicals, Inc.

Neuropsychological correlates of P50 sensory gating in patients with schizophrenia

Impaired inhibition of P50 cerebral evoked response is one of the best validated endophenotypes in schizophrenia. There are controversial data on the relationship between P50 evoked potential deficit and measures of cognitive function in schizophrenia. A comprehensive clinical and neurocognitive assessment plus an evaluation of P50 sensory gating was performed in 160 schizophrenia patients and 64 controls. Neurocognitive scores from each cognitive domain were converted to demographically-adjusted T-scores (age, gender, and years of education) for all study participants. The relationship between P50 and neurocognitive variables was assessed via parametric and nonparametric correlations and categorical strategies: we compared neuropsychological test scores in patients and controls in the lowest P50 quartile vs. the highest. Controls had better performance than schizophrenia patients in all cognitive domains. Schizophrenia patients had significantly higher P50 ratios than controls, and no significant correlation was found between P50 gating measures and neuropsychological test scores in schizophrenia patients or healthy controls. Moreover, no differences in neurocognitive performance were found between subjects in the lowest P50 ratio quartile vs. the highest in healthy controls or patients with schizophrenia. We concluded that there is no evidence of an association between P50 ratio and cognitive measures in schizophrenia patients, and this seems to be also the case in healthy controls.

NMDA antagonist MK801 recreates auditory electrophysiology disruption present in autism and other neurodevelopmental disorders

Autism is a highly disabling neurodevelopmental disorder characterized by social deficits, language impairment, and repetitive behaviors. There are few effective biological treatments for this disorder, partly due to the lack of translational biomarkers. However, recent data suggest that autism has reliable electrophysiological endophenotypes, along with evidence that some deficits may be caused by NMDA receptor (NMDAR) dysfunction. Similarly, the NMDAR antagonist MK801 has been used in behavioral animal models of autism. Since MK801 has also been used as a model of schizophrenia, this paper examines the independent and overlapping ways in which MK801 recreates the electrophysiogical changes present in both diseases. Mouse EEG was recorded in response to auditory stimuli after either vehicle or MK801 and the dose-response relationship for each measure was determined. ERP component amplitude and latency analysis was performed along with time-frequency analysis of gamma frequency inter-trial coherence and evoked power. Evoked gamma power and ITC were decreased by MK801 at the highest dose. P1, N1 latency and gamma baseline power were increased in dose dependent fashion following MK801. There were no amplitude changes in P1 or N1. MK801 caused alterations in evoked gamma activity, gamma ITC, gamma baseline power, P1 and N1 latency similar to findings in autism. These data provide evidence indicating that NMDAR dysfunction may contribute to deficits specific to autism and some that overlap with other disorders such as schizophrenia. Such observations could be important for developing novel therapeutics, as electrophysiological endophenotypes associate with functional measures and may provide early biomarkers for efficacy in clinical trials.