Olfactory hallucinations in schizophrenia and schizoaffective disorder: a neuropsychological investigation

Purpose: The primary aim of this research was to address the current gap in knowledge of olfactory hallucinations (OHs), specifically within the schizophrenia population. This aim was addressed by employing a symptom-focused approach that combined clinical neuropsychological and cognitive neuropsychological perspectives to inform the understanding of the neural, neuropsychological and cognitive causes of OHs. Method: Two groups of clinical patients (one comprised of those self-reporting recent OHs (n = 11) and another self-reporting auditory verbal hallucinations (AVHs - with no lifetime history of OHs; n = 10)), in addition to a group of healthy controls (n = 18) completed a battery of neuropsychological tasks tapping into executive and amygdala functioning. An odour source discrimination task and an auditory verbal source monitoring task was also completed. Results: Evidence of smell identification impairment and aspects of general executive dysfunction was found in both clinical groups relative to controls. However, a pattern of dysfunction that particularly implicates OFC and amygdala neural circuitry (and disruption to their associated higher level neuropsychological skills) was also found that was specific to patients experiencing OHs. On tasks of source monitoring, preliminary evidence was found on the odour source discrimination task suggestive of a sensory specific source monitoring bias for patients with schizophrenia who experience OHs. In addition, a specific source monitoring deficit for auditory-verbal information was also found in patients that experience AVHs. Conclusion: The obtained results suggest that the generation of OHs may be underpinned by a combination of specific neuronal and related source monitoring dysfunction. This finding has implications for therapy in individuals with schizophrenia who experience OHs.