Early auditory processing dysfunction in schizophrenia: Mechanisms and implications

Finding the Right Dose: NMDA Receptor-Modulating Treatments for Cognitive and Plasticity Deficits in Schizophrenia and the Role of Pharmacodynamic Target Engagement

Cognitive impairment associated with schizophrenia (CIAS) and related deficits in learning (plasticity) are among the leading causes of disability in schizophrenia. Despite this, there are no Food and Drug Administration-approved treatments for CIAS, and the development of treatments has been limited by numerous phase 2/3 failures of compounds that showed initial promise in small-scale studies. NMDA-type glutamate receptors (NMDARs) have been proposed to play an important role in schizophrenia; moreover, the NMDAR has a well-characterized role in cognition, learning, and neuroplasticity. We review previously published clinical trials in CIAS that focused on NMDAR modulator treatments, focusing on published and recent developments of the use of novel NMDAR-modulating treatments for CIAS both alone and combined with plasticity/learning paradigms to enhance learning. We use this discussion of previous studies to highlight the importance of incorporating pharmacodynamic target engagement biomarkers early in treatment development, which can help predict which compounds will succeed or fail in phase 3. A range of direct and indirect NMDAR modulators are covered, including D-serine, D-cycloserine, memantine, and glycine and first-generation glycine transport inhibitors (e.g., sarcosine and bitopertin), as well as recent positive studies of iclepertin, a novel glycine transport inhibitor, and luvadaxistat, a D-amino acid oxidase inhibitor that increases brain D-serine levels, and indirect noninvasive brain stimulation NMDAR-modulating treatments. Several examples of successful use of pharmacodynamic target engagement biomarkers for dose/drug discovery are emphasized, including the mismatch negativity, auditory steady state, and time-frequency event-related potential approaches.

Early auditory impairments as a candidate marker of attenuated sensory symptoms of psychosis

BACKGROUND AND HYPOTHESIS

Deficits in early auditory processing (EAP), as indexed by tone-matching performance, have been consistently demonstrated in individuals with schizophrenia spectrum disorders. However, the ontogeny of tone-matching deficits in schizophrenia remains relatively unknown. The current study aims to determine the relationship between clinical high risk for psychosis and EAP.

STUDY DESIGN

We employed a web-based screening approach to identify CHR individuals. A sample of 892 community dwelling participants completed the 16-tem version of the prodromal questionnaire (PQ16) for the assessment of attenuated psychotic symptoms, a 9-item questionnaire of perceptual and cognitive aberrations (PCA) for the assessment of basic symptoms and a tone-matching task.

STUDY RESULTS

505 (43.4 %) participants met cut-off criteria for attenuated psychotic symptoms (PQ16 ≥ 6 endorsed items), 614 (68.3 %) for basic symptoms (PCA ≥ 3 endorsed items), 647 (72.0 %) for either and 358 (40.1 %) for both of them. No significant differences in tone-matching performance were observed between CHR and non-CHR subjects, using either attenuated psychotic symptoms, basic symptoms, either or both cutoffs. In the CHR group screened with attenuated psychotic symptoms, auditory and tactile sensory symptoms were significantly associated with tone-matching deficits.

CONCLUSION

Tone-matching may not serve as a reliable biomarker for CHR status but rather a risk marker for the emergence of early sensory manifestations.

Validation of the Comprehensive and Brief International Classification of Functioning, Disability and Health Core Sets for Schizophrenia from the Perspective of Individuals Diagnosed with the Disorder: A Worldwide Study Using Focus Groups

The comprehensive and brief International Classification of Functioning, Disability and Health (ICF) core sets for schizophrenia, based on the World Health Organization (WHO) framework, aim to describe the functioning of individuals with schizophrenia. The objective of this study was to identify the most common problems faced by these individuals and validate the ICF core sets. Eight focus groups were conducted, recorded, and transcribed verbatim. The linking process involved two independent coders identifying meaningful units and linking agreed-upon concepts to the ICF categories. Data saturation was defined as the point at which no new categories emerged from additional focus groups. The 37 participants in this study represented the WHO regions of Africa, South-East Asia, the Western Pacific, and Europe. The focus groups confirmed the relevance of all ICF core set categories, with an additional 21 second-level categories being proposed in at least six of the eight focus groups. In this study, the ICF core sets for schizophrenia were validated from the perspective of individuals. However, several second-level categories not currently included in the ICF core sets also emerged. To ensure that the ICF core sets are truly international in scope, the potential relevance of these categories should be investigated further.

Mechanistic account of the left auditory cortex for tone-matching in schizophrenia: A pilot transcranial random noise stimulation (tRNS) sham-controlled study

OBJECTIVE

Deficits in the ability to match tones following brief delay and their contribution to higher-order cognitive alterations have been repeatedly documented in schizophrenia. The aim was to explore if left fronto-temporal high-frequency transcranial random noise stimulation (hf-tRNS), with electrodes placed over brain regions involved in tone-matching would significantly modulate performances in participants with schizophrenia.

METHODS

In a randomized, double-blind sham-controlled study, 10 participants with schizophrenia were allocated to receive ten sessions of either active or sham hf-tRNS. The anode was placed over the left prefrontal cortex and the cathode over the left temporoparietal junction. A tone-matching task was administered before and after the hf-tRNS.

RESULTS

We calculated the changes in tone-matching performance before and after hf-tRNS session in each group. A significant between-group difference was observed for the difficult tone-matching conditions (W= 14.500, p = 0.032), with tone-matching improvement in the sham group and no improvement in the active group.

DISCUSSION

hf-tRNS could disrupt the test-retest learning effect in the tone-matching task in individuals with schizophrenia. It is likely that this disruption resulted from cathodal-induced inhibition of the functional coupling between auditory cortical areas that correlates with tone-matching performance in patients.

CONCLUSION

The findings contribute to our understanding of hf-tRNS effects on early auditory processing in schizophrenia.

The Less Things Change, the More They Remain the Same: Impaired Neural Plasticity as a Critical Target for Drug Development in Neuropsychiatry

Neuropsychiatric disability is related to reduced ability to change in response to clinical interventions, e.g., plasticity. Study of biomarkers and interventional strategies for plasticity, however, are sparse. In this chapter, we focus on the serial frequency discrimination task (SFDT), which is sensitive to impairments in early auditory processing (EAP) and auditory learning and has been most thoroughly studied in dyslexia and schizophrenia. In the SFDT, participants are presented with repeated paired tones ("reference" and "test") and indicate which tone is higher in pitch. Plasticity during the SFDT is critically dependent upon interactions between prefrontal "cognitive control" regions, and lower-level perceptual and motor regions that may be detected using both fMRI and time-frequency event-related potential (TF-ERP) approaches. Additionally, interactions between the cortex and striatum give insights into glutamate/dopamine interaction mechanisms. The SFDT task has been utilized in the development of N-methyl-D-aspartate receptor (NMDAR) targeted medications, which significantly modulate sensory and premotor neurophysiological activity. Deficits in pitch processing play a critical role in impaired neuro- and social cognitive function in schizophrenia and may contribute to similar impairments in dyslexia. Thus, the SFDT may be ideal for development of treatments aimed at amelioration of neuro- and social cognitive deficits across neuropsychiatric disorders.

Mismatch Negativity (MMN) as a Pharmacodynamic/Response Biomarker for NMDA Receptor and Excitatory/Inhibitory Imbalance-Targeted Treatments in Schizophrenia

Schizophrenia is a major mental disorder that affects approximately 0.5% of the population worldwide. Persistent negative symptoms and cognitive impairments associated with schizophrenia (CIAS) are key features of the disorder and primary predictors of long-term disability. At the neurochemical level, both CIAS and negative symptoms are potentially attributable to dysfunction or dysregulation of N-methyl-D-aspartate receptor (NMDAR)-mediated neurotransmission within cortical and subcortical brain regions. At present, there are no approved treatments for either CIAS or persistent negative symptoms. Development of novel treatments, moreover, is limited by the lack of biomarkers that can be used translationally across preclinical and early-stage clinical investigation. The present chapter describes the use of mismatch negativity (MMN) as a pharmacodynamic/response (PD/R) biomarker for early-stage clinical investigation of NMDAR targeted therapies for schizophrenia. MMN indexes dysfunction of early auditory processing (EAP) in schizophrenia. In humans, deficits in MMN generation contribute hierarchically to impaired cognition and functional outcome. Across humans, rodents, and primates, MMN has been linked to impaired NMDAR function and resultant disturbances in excitatory/inhibitory (E/I) balance involving interactions between glutamatergic (excitatory) pyramidal and GABAeric (inhibitory) local circuit neurons. In early-stage clinical trials, MMN has shown sensitivity to the acute effects of novel pharmacological treatments. These findings support use of MMN as a pharmacodynamic/response biomarker to support preclinical drug discovery and early-stage proof-of-mechanisms studies in schizophrenia and other related neuropsychiatric disorders.

Abnormal phase entrainment of low- and high-gamma-band auditory steady-state responses in schizophrenia

Introduction

Gamma-band oscillatory deficits have attracted considerable attention as promising biomarkers of schizophrenia (SZ). Notably, a reduced auditory steady-state response (ASSR) in the low gamma band (40 Hz) is widely recognized as a robust finding among SZ patients. However, a comprehensive investigation into the potential utility of the high-gamma-band ASSR in detecting altered neural oscillations in SZ has not yet been conducted.

Methods

The present study aimed to assess the ASSR using magnetoencephalography (MEG) data obtained during steady-state stimuli at frequencies of 20, 30, 40, and 80 Hz from 23 SZ patients and 21 healthy controls (HCs). To evaluate the ASSR, we examined the evoked power and phase-locking factor (PLF) in the time-frequency domain for both the primary and secondary auditory cortices. Furthermore, we calculated the phase-locking angle (PLA) to examine oscillatory phase lead or delay in SZ patients. Taking advantage of the high spatial resolution of MEG, we also focused on the hemispheric laterality of low- and high-gamma-band ASSR deficits in SZ.

Results

We found abnormal phase delay in the 40 Hz ASSR within the bilateral auditory cortex of SZ patients. Regarding the 80 Hz ASSR, our investigation identified an aberrant phase lead in the left secondary auditory cortex in SZ, accompanied by reduced evoked power in both auditory cortices.

Discussion

Given that abnormal phase lead on 80 Hz ASSR exhibited the highest discriminative power between HC and SZ, we propose that the examination of PLA in the 80 Hz ASSR holds significant promise as a robust candidate for identifying neurophysiological endophenotypes associated with SZ. Furthermore, the left-hemisphere phase lead observed in the deficits of 80 Hz PLA aligns with numerous prior studies, which have consistently proposed that SZ is characterized by left-lateralized brain dysfunctions.

Why mismatch negativity continues to hold potential in probing altered brain function in schizophrenia

The brain potential known as mismatch negativity (MMN) is one of the most studied indices of altered brain function in schizophrenia. This review looks at what has been learned about MMN in schizophrenia over the last three decades and why the level of interest and activity in this field of research remains strong. A diligent consideration of available evidence suggests that MMN can serve as a biomarker in schizophrenia, but perhaps not the kind of biomarker that early research supposed. This review concludes that MMN measurement is likely to be most useful as a monitoring and response biomarker enabling tracking of an underlying pathology and efficacy of interventions, respectively. The role of, and challenges presented by, pre-clinical models is discussed as well as the merits of different methodologies that can be brought to bear in pursuing a deeper understanding of pathophysiology that might explain smaller MMN in schizophrenia.

Deficient Audiovisual Speech Perception in Schizophrenia: An ERP Study

In everyday verbal communication, auditory speech perception is often disturbed by background noise. Especially in disadvantageous hearing conditions, additional visual articulatory information (e.g., lip movement) can positively contribute to speech comprehension. Patients with schizophrenia (SZs) demonstrate an aberrant ability to integrate visual and auditory sensory input during speech perception. Current findings about underlying neural mechanisms of this deficit are inconsistent. Particularly and despite the importance of early sensory processing in speech perception, very few studies have addressed these processes in SZs. Thus, in the present study, we examined 20 adult subjects with SZ and 21 healthy controls (HCs) while presenting audiovisual spoken words (disyllabic nouns) either superimposed by white noise (-12 dB signal-to-noise ratio) or not. In addition to behavioral data, event-related brain potentials (ERPs) were recorded. Our results demonstrate reduced speech comprehension for SZs compared to HCs under noisy conditions. Moreover, we found altered N1 amplitudes in SZ during speech perception, while P2 amplitudes and the N1-P2 complex were similar to HCs, indicating that there may be disturbances in multimodal speech perception at an early stage of processing, which may be due to deficits in auditory speech perception. Moreover, a positive relationship between fronto-central N1 amplitudes and the positive subscale of the Positive and Negative Syndrome Scale (PANSS) has been observed.

Augmentation of learning in schizophrenia by D-serine is related to auditory and frontally-generated biomarkers: A randomized, double-blind, placebo-controlled study

Auditory cognition is impaired in schizophrenia, and typically engages a complex, distributed, hierarchical network, including both auditory and frontal input. We recently demonstrated proof of principle for the target engagement of an N-methyl-D-aspartate-type glutamate receptor (NMDAR) agonist + auditory targeted remediation (d-serine+AudRem) combination, showing significant improvement in auditory-learning induced plasticity and mismatch negativity. In this secondary analysis, we report on frontal EEG outcomes, assessing for both generalized effects and the mechanism of auditory plasticity. 21 schizophrenia or schizoaffective disorder participants were randomized to three 1x weekly AudRem + double-blind d-serine (100 mg/kg) visits. In AudRem, participants indicated which paired tone was higher in pitch. The focus of this secondary analysis was a frontally (premotor) mediated EEG outcome- event-related desynchronization in the b band (b-ERD), which was shown to be sensitive to AudRem in previous studies. d-Serine+AudRem led to significant improvement in b-ERD power across the retention and motor preparation intervals (F 1,18 =6.0, p=0.025) vs. AudRem alone. b-ERD was significantly related to baseline cognition, but not auditory-learning induced plasticity. The principal finding of this prespecified secondary analysis are that in addition to improving auditory based biomarkers, the d-serine+AudRem combination led to significant improvement in biomarkers thought to represent frontally mediated dysfunction, suggesting potential generalization of effects. Changes in auditory-learning induced plasticity were independent of these frontally mediated biomarkers. Ongoing work will assess whether d-serine+AudRem is sufficient to remediate cognition or whether targeting frontal NMDAR deficits with higher-level remediation may also be required. Trial Registration: NCT03711500.

Feasibility and clinical utility of using the tone matching test for assessment of early auditory processing in schizophrenia

Early auditory processing (EAP) deficits are prevalent in schizophrenia and linked to disturbances in higher order cognition and daily functioning. Treatments that target EAP have the potential to drive downstream cognitive and functional improvements, but clinically feasible means to detect EAP impairment are lacking. This report describes the clinical feasibility and utility of using the Tone Matching (TM) Test to assess EAP in adults with schizophrenia. Clinicians were trained to administer the TM Test as part of a baseline cognitive battery to inform choice of cognitive remediation (CR) exercises. Only if the TM Test indicated EAP impairment, were the recommended CR exercises to include EAP training. Results indicated clinicians included the TM Test in all baseline assessments and identified 51.72% as EAP impaired. There were significant positive relationships between TM Test performance and cognitive summary scores, confirming instrumental validity. All clinicians found the TM Test useful for CR treatment planning. CR participants with impaired EAP spent significantly more training time on EAP exercises compared to CR participants with intact EAP (20.11% vs 3.32%). This study found that it is feasible to use the TM Test in community clinics and the test was perceived as clinically useful for personalizing treatment.