Schizophrenia (SZ) is a complex and chronic psychotic disorder that affects approximately 1% of the world's population and is associated with positive, negative, and cognitive symptoms. Auditory verbal hallucinations (AVHs) are a key symptom of SZ that cause functional impairments and distress. Despite antipsychotic medication treatments, 25% of patients experience medication resistant AVHs. Additional research into the underlying neuronal mechanisms of AVHs is needed to develop alternative treatments. The mismatch negativity (MMN) is an auditory event-related potential that represents pre-attentive detection of stimulus deviance. MMN deficits are prominent in SZ and are associated with greater AVH frequency. MMN deficits may also be related to qualitative features of AVHs, which have yet to be extensively assessed.
The primary aim of this work was to assess differences in MMN features (amplitude and latency) between SZ patients and healthy controls (HCs) using two different versions of the MMN five deviant multi-feature task (pure tone and speech-based sounds). The second aim was to examine relationships between MMN features, clinical ratings of AVH severity (The Psychotic Symptom Rating Scale [PSYRATS] total score, Positive and Negative Syndrome Scale [PANSS] item 3 ["hallucinatory behaviour"]) and self-report measures of AVH features in SZ patients (i.e., the Beliefs About Voices Questionnaire-Revised [BAVQ-R], Voice Acceptance and Action Scale [VAAS] and the Voice Power Differential Scale [VPDS]), the latter has yet to be assessed. The secondary aim was to directly compare differences in the MMN responses between SZ and HC groups across the two tasks. Finally, exploratory aims included examining differences in MMN responses to low and high frequency and intensity deviants in the tone task and assessing differences in the MMN response between groups at the mastoid sites (TP9/TP10), where the polarity reversal of the MMN occurs. These more methodological aims have not been previously assessed, to our knowledge.
The SZ group (n = 16) had significantly smaller MMN amplitudes to the frequency, gap and intensity deviants compared to the HC group (n = 17) in the MMN tone task. In the MMN speech task, the SZ group had significantly smaller MMN amplitudes to the frequency, intensity, vowel duration and consonant deviants compared to the HC group. The correlation analysis revealed that the most pronounced relation was a positive association between MMN amplitudes to the intensity deviant (tone task) and total scores on the VPDS (i.e., smaller/less negative MMN amplitudes were associated with higher VPDS scores). For the secondary analyses, the SZ group had smaller MMN amplitudes to the frequency deviant in both the tone and speech MMN tasks. Finally, the exploratory mastoid analysis in the tone task revealed that the SZ group had smaller MMN amplitudes to the frequency deviant at both mastoid sites. In the speech task, MMN amplitudes were larger at the left mastoid site (TP9) compared to the right mastoid site (TP10) across all deviant types. The HC group also had larger MMN amplitudes at the left mastoid site (TP9) compared to the SZ group.
This study revealed MMN deficits in SZ patients across a variety of deviant types, including both pure tone deviants and speech-based deviants. MMN deficits were most pronounced for the frequency and intensity deviants across both tasks, suggesting that SZ patients with persistent AVHs may have more generalized deficits in the automatic processing of basic units of speech and pure tones, rather than impaired processing of specific acoustic features. Associations between MMN features and subjective measures of AVHs revealed that impaired processing of pure tone intensity deviants is related with a greater perceived "power" of the voice, impaired processing of speech-based frequency deviants is related to greater clinical AVH severity, and that impaired and less efficient processing of both vowel and pure tone deviants are related to a higher perceived hostility of the voice. This study adds valuable information to the literature regarding relationships between MMN features and subjective aspects of the AVH experience in SZ patients. Importantly, this work is novel as it is the first to directly compare MMN responses across two tasks (speech and sound) in SZ patients with persistent AVHs. This thesis emphasizes the importance of examining subjective aspects of the AVH experience in the context of the MMN to gather a more complete understanding of how AVHs are impacting brain responses.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/44253 |
| Date | 11 November 2022 |
| Creators | Schryver, Bronwen |
| Contributors | Jaworska, Natalia |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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