Growing evidence supports the effectiveness of cognitive behavioural therapy (CBT) for psychosis, including CBT for voices (CBTv), which targets auditory verbal hallucinations (AVH). CBT may be a promising approach for improving information processing difficulties in schizophrenia, and by so doing, facilitating social cognition and daily functioning. While many studies have tested treatment effects in schizophrenia, none have specifically evaluated electrophysiological changes in brain activity following CBT in patients with schizophrenia.
Electrophysiological studies have revealed a number of event related potentials (ERPs) associated with impaired processing of emotional facial expressions in patients with schizophrenia. This well-documented difficulty with facial expression recognition has been associated with impaired low-level visual information processing. However, there is only limited and inconsistent data on the way in which early visual processing deficits are related to impaired emotional expression processing in this patient population. The research presented in this thesis assessed changes in ERPs to emotional expressions following cognitive behavioural therapy for voices (CBTv) in patients with schizophrenia who experience auditory hallucinations. The studies presented also examined ERPs evoked in response to spatial frequency filtered (SF-filtered) and unfiltered images of facial expressions and control objects in healthy controls and a homogenous sample of schizophrenia patients – those experiencing auditory verbal hallucinations. This was done to test certain hypotheses regarding the low-level genesis of face recognition difficulties in schizophrenia.
Relative to controls, patients with schizophrenia indicated blunted: 1) early-stage visual information processing to sad, angry and fearful facial expressions (as indexed by the amplitude of the P100 ERP), 2) facial structural encoding to neutral, joyful, sad, angry and fearful facial expression (as indexed by the N170), and 3) higher-order decoding of all facial expressions (indexed by mean amplitude of the P300). Assessment of SF-filtered facial expressions found impaired early processing (i.e., P100) specific to low spatial frequency (LSF) filtered fearful facial expression and high spatial frequency (HSF) filtered neutral faces in patients with schizophrenia, which at later stages (i.e., N170 and P300) extended to all facial expressions and SF filtering conditions. Within-group comparisons showed that patients exhibited a different pattern of ERP modulation across facial expressions than controls for P100 and N170, but not for P300. The within-group comparisons also suggested a heightened response to LSF threatening information, relative to BSF conditions, in the patient group.
CBTv therapy did not change ERP amplitudes in response to facial expressions, but was associated with decreased latency in the P100. This improved processing speed was not reflected in later ERP components (i.e., N170 and P300).
These results indicate that earlier perceptual processing impairments are expression-specific and that behavioural and electrophysiological face-processing deficits in schizophrenia arise from early-stage deficits in visual processing. The finding of an improvement in visual processing speed to facial expressions following CBTv treatment provides the first demonstration of CBTv-induced changes to brain responses to facial expressions at an early neural processing stage.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/38500 |
| Date | 29 November 2018 |
| Creators | Shah, Dhrasti K. |
| Contributors | Collin, Charles |
| 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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