This study aims to determine if individuals with schizophrenia have greater reactivity to vestibular stimulation than healthy controls. The physiological response of vestibular stimulation will be assessed with electronystagmography, which provides a measure of the intensity of the nystagmus via PSPV. Positive results would suggest greater vestibular system reactivity to vestibular stimulation may be a biomarker of schizophrenia. Pathophysiologically, increased vestibular reactivity to vestibular stimulation may reflect abnormal vestibular function or impaired central suppression of the vestibular ocular reflex.

In schizophrenia, there is no conclusive link between psychopathology and vestibular dysfunction and we are not aware of any data that exists on the range of responses to caloric vestibular stimulation (CVS) in persons with schizophrenia. Initial data from another CVS study from our group suggests individuals with schizophrenia have greater reactivity to body temperature (37°C) CVS, as measured by the peak slow phase velocity of the resulting nystagmus (PSPV), than would be expected from individuals without schizophrenia versus healthy participants. Intriguingly, CVS at 37°C should not theoretically produce a significant vestibulocular reflex response due to the stimulus' approximation to body temperature. Hence, the primary aim of this study is to determine if individuals with schizophrenia will have greater vestibular reactivity, as measured by nystagmus PSPV, to CVS in comparison with healthy participants. The secondary aim is to assess illness awareness pre and post CVS administration in attempts to replicate our previous observation. A total of 20 patients with schizophrenia and 20 healthy control participants will be recruited. All participants will receive three conditions bilaterally: (1) body temperature (37°C) vestibular stimulation; (2) warm CVS (44°C), and (3) cold CVS (30°C).

Inclusion Criteria for Schizophrenia group:

1. Male or female inpatients or outpatients age ≥18
2. Having a DSM-5 diagnosis of schizophrenia or schizoaffective disorder
3. Voluntary and capable of consenting to participation in the research study
4. Fluent in English

Inclusion Criteria for Healthy Controls group:

1. Male or female and age ≥18
2. Voluntary and capable of consenting to participation in the research study
3. Fluent in English
4. Absence of history of psychiatric illness using the Mini-International Neuropsychiatric Interview (MINI)

Exclusion Criteria for all participants:

1. Serious unstable medical illness or any concomitant major medical or neurological illness
2. Acute suicidal and/or homicidal ideation
3. Formal thought disorder rating of over 2 on the Scale for Assessment of Positive Symptoms (SAPS) [patients only]
4. DSM-IV substance dependence (except caffeine and nicotine) within one month prior to entering the study
5. Pregnant women
6. Positive urine drug screen
7. History of external or middle ear pathology
8. History or signs of middle ear surgery (e.g. Tympanoplasty, mastoidectomy)
9. Signs of active ear disease

The participant will be blinded to the order of experimental conditions, as well as the person conducting specific ratings assessments.