Magnetoencephalographic recording of auditory mismatch negativity in response to duration and frequency deviants in a single session in patients with schizophrenia

Reduction of phonetic mismatch negativity may depict illness course and predict functional outcomes in schizophrenia

Schizophrenia (SZ) is characterized by a series of cognitive impairments, including automatic processing impairment of basic auditory information, indexed by mismatch negativity (MMN). Existing studies mainly focus on MMN induced by deviant of single acoustic features, and relatively few studies have focused on complex acoustic stimuli, especially speech-induced MMN. Many cognitive impairments in SZ are related to speech function. Thus, the present study aimed to examine the reduction of phonetic MMN in SZ as a potential biomarker and its relationship with illness course and functional outcomes. Electroencephalogram (EEG) signals were recorded from 32 SZ and 32 healthy controls (HC) in a double oddball paradigm, with /da/ as the standard stimulus and /ba/ and /du/ as the deviant stimuli. MMN was computed for vowel and consonant deviants separately. Clinical symptoms were assessed using the Positive and Negative Symptom Rating Scale (PANSS). Illness duration and illness relapse were acquired by combining clinical interviews and electronic medical records. Functional outcomes were assessed using the Global Assessment of Functioning scale (GAF). Compared with HC, SZ showed lower amplitudes of phonetic MMN, especially for vowel deviants. In addition, the MMN amplitude of the vowel deviant was significantly correlated with illness duration, illness relapse, and functional outcomes among patients with SZ. These findings indicate that the pre-attentive automatic phonetic processing of SZ was impaired for both consonants and vowels, while the vowel processing deficit may be the key speech processing deficit in SZ, which could depict the illness course and predict the functional outcomes.

Omission mismatch negativity of speech sounds reveals a functionally impaired temporal window of integration in schizophrenia

OBJECTIVE

We hypothesized that sensory memory associated with the temporal window of integration (TWI) would be impaired in patients with schizophrenia, an issue that had not been evaluated using omission mismatch negativity (MMN) of complex speech sounds. We aimed to assess the functional changes in auditory sensory memory associated with the TWI in patients with schizophrenia by investigating the effect of omission of complex speech stimuli on the MMN.

METHODS

In total, 17 patients with schizophrenia and 15 control individuals participated in the study. The MMN in response to omission deviants of complex speech sounds was recorded, while the participants were instructed to ignore the series of speech sounds.

RESULTS

The MMN latency in patients with schizophrenia was significantly prolonged by deviant stimuli to omissions corresponding to the early and late parts of the temporal TWI. There were no significant group differences in the amplitude of the MMN to omissions at different time points across the TWI.

CONCLUSIONS

Our results suggested that sensory tracing function in patients with schizophrenia is impaired in the early and the later half of the TWI.

SIGNIFICANCE

We showed that certain MMN abnormalities in patients with schizophrenia may be caused by an impaired TWI.

Do rat auditory event related potentials exhibit human mismatch negativity attributes related to predictive coding?

Rodent models play a significant role in understanding disease mechanisms and the screening of new treatments. With regard to psychiatric disorders such as schizophrenia, however, it is difficult to replicate the human symptoms in rodents because these symptoms are often either 'uniquely human' or are only conveyed via self-report. There is a growing interest in rodent mismatch responses (MMRs) as a translatable 'biomarker' for disorders such as schizophrenia. In this review, we will summarize the attributes of human MMN, and discuss the scope of exploring the attributes of human MMN in rodents. Here, we examine how reliably MMRs that are measured in rats mimic human attributes, and present original data examining whether manipulations of stimulus conditions known to modulate human MMN, do the same for rat MMRs. Using surgically-implanted epidural electroencephalographic electrodes and wireless telemetry in freely-moving rats, we observed human-like modulations of MMRs, namely that larger MMRs were elicited to unexpected (deviant) stimuli that a) had a larger change in pitch compared to the expected (standard) stimulus, b) were less frequently presented (lower probability), and c) had no jitter (stable stimulus onset asynchrony) compared to high jitter. Overall, these findings contribute to the mounting evidence for rat MMRs as a good analogue of human MMN, bolstering the development of a novel approach in future to validate the preclinical models based on a translatable biomarker, MMN.

Auditory Mismatch Negativity Under Predictive Coding Framework and Its Role in Psychotic Disorders

Traditional neuroscience sees sensory perception as a simple feedforward process. This view is challenged by the predictive coding model in recent years due to the robust evidence researchers had found on how our prediction could influence perception. In the first half of this article, we reviewed the concept of predictive brain and some empirical evidence of sensory prediction in visual and auditory processing. The predictive function along the auditory pathway was mainly studied by mismatch negativity (MMN)-a brain response to an unexpected disruption of regularity. We summarized a range of MMN paradigms and discussed how they could contribute to the theoretical development of the predictive coding neural network by the mechanism of adaptation and deviance detection. Such methodological and conceptual evolution sharpen MMN as a tool to better understand the structural and functional brain abnormality for neuropsychiatric disorder such as schizophrenia.

Oscillatory biomarkers of early auditory information processing predict cognitive gains following targeted cognitive training in schizophrenia patients

Auditory-based targeted cognitive training (TCT) is an effective and well-validated intervention for the treatment of cognitive impairment in schizophrenia patients. Improvements in higher-order cognition, reductions in symptom severity, and increases in psychosocial functioning secondary to TCT are thought to be driven by "bottom-up" enhancement of early auditory information processing (EAIP). Despite strong evidence of efficacy at the group level, there is significant variability in response to TCT, with few well-delineated biomarkers for predicting individual benefit. EEG biomarkers of EAIP are indicators of early-treatment sensitivity that predict full-course TCT outcome; however, further characterization is necessary for biomarker-guided clinical trials. The current study examined baseline and early-treatment sensitivity (i.e., change from baseline after 1 h) in theta band oscillatory activity to deviant stimuli as moderators of full course (30 h) TCT response in treatment-refractory schizophrenia patients randomly assigned to receive either treatment-as-usual (TAU; n = 22) or TAU augmented with TCT (n = 30). Theta evoked power and phase locking at baseline predicted patient improvements in global cognitive function after 30 h of TCT. Decrease in theta activity to deviant stimuli after 1 h of TCT predicted improvements in verbal learning after 30 h. Exploratory analyses using EEG composite scores had high levels of sensitivity and specificity for identifying patients most likely to benefit from TCT. The integrity of baseline neurophysiologic activity associated with EAIP, as well as the sensitivity of the underlying circuity to change, likely reflects an intermediate therapeutic process underlying the effectiveness of TCT that can be used to predict patient response to treatment.

Decomposing the constituent oscillatory dynamics underlying mismatch negativity generation in schizophrenia: Distinct relationships to clinical and cognitive functioning

Abnormalities in early auditory information processing (EAIP) contribute to higher-order deficits in cognition and psychosocial functioning in schizophrenia. A passive auditory oddball paradigm is commonly used to evoke event-related potential (ERP) measures of EAIP reflecting auditory sensory registration and deviance detection, including mismatch negativity (MMN) and P3a responses. MMN and P3a have been extensively studied in healthy subjects and neuropsychiatric patient populations and are increasingly used as translational biomarkers in the development of novel therapeutics. Despite widespread use, relatively few studies have examined the constituent oscillatory elements and the extent to which sensory registration and deviance detection represent distinct or intercorrelated processes. This study aimed to determine the factor structure and clinical correlates of these oscillatory measures in schizophrenia patients (n = 706) and healthy comparison subjects (n = 615) who underwent clinical, cognitive, and functional characterization and EEG testing via their participation in the Consortium of Genomics in Schizophrenia (COGS-2) study. Results revealed significant deficits in theta-band (4-7 Hz) evoked power and phase locking in patients. Exploratory factor analyses of both ERP and oscillatory measures revealed two dissociable factors reflecting sensory registration and deviance detection. While each factor shared a significant correlation with social cognition, the deviance detection factor had a unique relationship to multiple cognitive and clinical domains. Results support the continued advancement of functionally relevant oscillatory measures underlying EAIP in the development of precognitive therapeutics.

Neurophysiologic measures of target engagement predict response to auditory-based cognitive training in treatment refractory schizophrenia

Cognitive impairment is a core feature of schizophrenia and a strong predictor of psychosocial disability. Auditory-based targeted cognitive training (TCT) aims to enhance verbal learning and other domains of cognitive functioning through "bottom-up" tuning of the neural systems underlying early auditory information processing (EAIP). Although TCT has demonstrated efficacy at the group level, individual response to TCT varies considerably, with nearly half of patients showing little-to-no benefit. EEG measures of EAIP, mismatch negativity (MMN) and P3a, are sensitive to the neural systems engaged by TCT exercises and might therefore predict clinical outcomes after a full course of treatment. This study aimed to determine whether initial malleability of MMN and P3a to 1-h of auditory-based TCT predicts improvements in verbal learning and clinical symptom reduction following a full (30-h) course of TCT. Treatment refractory patients diagnosed with schizophrenia were randomly assigned to receive treatment-as-usual (TAU; n = 22) or TAU augmented with TCT (n = 23). Results indicated that malleability (i.e., change from baseline after the initial 1-h dose of TCT) of MMN and P3a predicted improvements in verbal learning as well as decreases in the severity of positive symptoms. Examination of MMN and P3a malleability in patients after their first dose of TCT can be used to predict clinical response to a full course of treatment and shows promise for future biomarker-informed treatment assignment.

Lack of correlation between phonetic magnetic mismatch field and plasma d-serine levels in humans

OBJECTIVE

Uncovering molecular bases for auditory language processing in the human brain is a fundamental scientific challenge. The power and latency of the magnetic mismatch field (MMF) elicited by phoneme change, which are magnetoencephalographic indices of language function in its early stage of information processing, are theoretically thought to be modulated by N-methyl-d-aspartate-type glutamate receptor (NMDAR) function, but no study has yet assessed this possibility. We have thus sought to demonstrate an association between phonetic MMF power/latency and levels of plasma d-serine, an intrinsic co-agonist of glycine binding sites on NMDAR, in adults.

METHODS

The MMF response to phoneme changes was recorded using 204-channel magnetoencephalography in 61 healthy, right-handed, Japanese adults. Plasma levels of d- and l-serine were measured for each participant.

RESULTS

We did not find a significant correlation between MMF power/latency and plasma serine levels.

CONCLUSIONS

Despite a sufficient sample size, we failed to find an association between the physiological markers of the early stage of information processing of language in the auditory cortex and biomarkers indexing glutamatergic function.

SIGNIFICANCE

Our study did not indicate that a molecular index of glutamatergic function could be a surrogate marker for the early stage of information processing of language in humans.

Sensory prediction errors in the continuum of psychosis

Sensory prediction errors are fundamental brain responses that signal a violation of expectation in either the internal or external sensory environment, and are therefore crucial for survival and adaptive behaviour. Patients with schizophrenia show deficits in these internal and external sensory prediction errors, which can be measured using electroencephalography (EEG) components such as N1 and mismatch negativity (MMN), respectively. New evidence suggests that these deficits in sensory prediction errors are more widely distributed on a continuum of psychosis, whereas psychotic experiences exist to varying degrees throughout the general population. In this paper, we review recent findings in sensory prediction errors in the auditory domain across the continuum of psychosis, and discuss these in light of the predictive coding hypothesis.

Mismatch negativity as a biomarker of theta band oscillatory dysfunction in schizophrenia

Mismatch negativity (MMN) is among the best established biomarkers of cortical dysfunction in schizophrenia. MMN generators are localized primarily to primary and secondary auditory regions, and are known to reflect activity mediated by cortical N-methyl-d-aspartate-type glutamate receptors (NMDAR). Nevertheless, mechanisms underlying MMN generation at the local circuit level remain incompletely understood. This review synthesizes recent advances in circuit-level conceptualization of MMN based upon neuro-oscillatory findings. In the neuro-oscillatory (aka event-related spectral perturbation, ERSP) approach, responses to sensory stimuli are decomposed into underlying frequency bands prior to analysis. MMN reflects activity primarily in theta (4-7Hz) frequency band, which is thought to depend primarily upon interplay between cortical pyramidal neurons and somatostatin (SST)-type local circuit GABAergic interneurons. Schizophrenia-related deficits in theta generation are also observed not only in MMN, but also in other auditory and visual contexts. At the local circuit level, SST interneurons are known to maintain tonic inhibition over cortical pyramidal interneurons. SST interneurons, in turn, are inhibited by a class of interneurons expressing vasoactive intestinal polypeptide (VIP). In rodents, SST interneurons have been shown to respond differentially to deviant vs. standard stimuli, and inhibition of SST interneurons has been found to selectively inhibit deviance-related activity in rodent visual cortex. Here we propose that deficits in theta frequency generation, as exemplified by MMN, may contribute significantly to cortical dysfunction in schizophrenia, and may be tied to impaired interplay between cortical pyramidal neurons and local circuit SST-type GABAergic interneurons.

Right hemisphere pitch-mismatch negativity reduction in patients with major depression: An MEG study

BACKGROUND

The mismatch negativity (MMN) component of the event-related potential and its magnetic counterpart, the MMNm, are generated by a mismatch between the physical features of a deviant stimulus and a neuronal sensory-memory trace produced by repetitive standard stimuli. Deficits in the MMN/MMNm have been reported in patients with major depression; however, the results are inconsistent. The present study investigated the pitch-MMNm in patients with major depression using whole-head 306-channel magnetoencephalography (MEG).

METHODS

Twenty patients with major depression and 36 healthy subjects participated in this study. Subjects were presented with two sequences of auditory stimuli. One consisted of 1000Hz standard signals (probability=90%) and 1200Hz deviant signals (probability=10%), while the other consisted of 1200Hz standard (90%) and 1000Hz deviant signals (10%). Event-related brain responses to standard tones were subtracted from responses to deviant tones.

RESULTS

Major depressive patients showed significantly reduced magnetic global field power (GFP) of MMNm in the right hemisphere (p=0.02), although no significant MMNm reduction was observed in the left hemisphere (p=0.81). Additionally, patients with major depression showed significantly earlier bilateral MMNm peak latencies (p=0.004). No significant associations were observed between MMNm variables and demographic data/clinical variables within the patients.

LIMITATIONS

We could not exclude the effects of antidepressants, mood stabilizers, or neuroleptics on the MMNm abnormalities found in patients with major depression. Sample size was also insufficient to permit subgroup analyses.

CONCLUSIONS

Patients with major depression exhibited reduced GFP of MMNm in the right hemisphere. The present study suggested that patients with major depression may have right hemispheric dominant preattentive dysfunction.

Identifying neurocognitive markers for outcome prediction of global functioning in individuals with first-episode and ultra-high-risk for psychosis

AIM

There is an increasing need for identifying neurocognitive predictors of global functional outcome in early psychosis toward optimizing an early intervention strategy.

METHODS

We conducted a longitudinal observational study to investigate an association between neurocognitive assessments at baseline and global functional outcome at an average of 1-year follow up. Participants included ultra-high-risk for psychosis (UHR) individuals who had not converted to psychosis during the follow-up period (UHR-NP) and those with first-episode psychosis (FEP). We evaluated neurocognition at baseline using the Brief Assessment of Cognition in Schizophrenia Japanese version, including Verbal Memory, Working Memory, Motor Speed, Verbal Fluency, Attention/Processing Speed, and Executive Function. We also assessed global functional outcome using the modified Global Assessment of Functioning (mGAF) scale both at baseline and after the follow-up period.

RESULTS

Thirty-four UHR-NP individuals (34/47, 72%) and 29 FEP individuals (29/36, 81%) completed assessment of neurocognitive function at baseline and functional outcome at follow up. In the UHR-NP group, Attention/Processing Speed was significantly associated with the mGAF score at follow up. In the FEP group, Executive Function was significantly associated with the average mGAF score during follow up.

CONCLUSION

Attention/Processing Speed and Executive Function at baseline may predict global functional outcome of early psychosis. These neurocognitive tests are easy to incorporate in clinical settings and, if replicated in independent samples, may be included in routine clinical assessments for prediction of functional outcome in early psychosis.

Familial Influences on Mismatch Negativity and Its Association with Plasma Glutamate Level: A Magnetoencephalographic Study in Twins

Mismatch negativity (MMN) or its magnetic counterpart (magnetic mismatch negativity; MMNm) is regarded as a promising biomarker for schizophrenia. Previous electroencephalographic studies of MMN have demonstrated a moderate-to-high heritability for MMN amplitudes. N-methyl-D-aspartate receptor-dependent glutamatergic neurotransmission is implicated in MMN generation. We hypothesized that the differences between identical twins in MMNm variables might be associated with differences in plasma levels of amino acids involved in glutamatergic neurotransmission. Thirty-three pairs of monozygotic (MZ) and 10 pairs of dizygotic (DZ) twins underwent MMNm recording. The MMNm in response to tone duration changes, tone frequency changes, and phonemic changes was recorded using 204-channel magnetoencephalography. Of these, 26 MZ and 7 DZ twin pairs underwent blood sampling for determination of plasma amino acid levels. MMNm peak strength showed relatively high correlations in both MZ and DZ twin pairs. The differences in MMNm latencies tended to correlate with the differences in plasma amino acid levels within MZ pairs, while no significant correlation was observed after the Bonferroni correction. We observed a familial trait in MMNm strength. The differences in MMN latency in MZ twins might be influenced by changes in glutamate levels and glutamate-glutamine cycling; however, the results need to be replicated.