Do loudness cues contribute to duration mismatch negativity reduction in schizophrenia?

The present study explored duration mismatch negativity (MMN) reduction in schizophrenia. Duration MMN studies usually employ tones of very short duration (< 200 ms). For stimuli < 200 ms in duration, an increment in duration is accompanied by an increase in perceived loudness. It was previously proposed that the effectiveness of duration MMN in revealing MMN reduction in schizophrenia might be explained by patients being insensitive to loudness cues and duration increments. In this study we equated loudness cues in a typical duration MMN paradigm and explored the effect of this manipulation on MMN amplitude reduction in schizophrenia. The manipulation had little effect on a healthy comparison group but had a marked effect on the MMN generated in the patient group who produced a significantly smaller MMN response to the regular duration deviant than to that in the equated loudness condition. This result was interpreted as demonstrating that patients exhibit a very marked insensitivity to duration increments.

Association between reduced duration mismatch negativity (MMN) and raised temporal discrimination thresholds in schizophrenia.

OBJECTIVE: The event-related potential known as mismatch negativity (MMN) is elicited whenever the auditory system detects a change against an invariant background of stimulation. A reduction in mismatch negativity is well established in schizophrenia. The present study explored the association between reduced duration mismatch negativity in schizophrenia and behavioural measures of temporal discrimination. METHOD: Mismatch negativity amplitude to duration increments (125 vs. 50 ms) was compared between individuals with schizophrenia and healthy controls. Mismatch negativity amplitude was also related to two behavioural measures of temporal discrimination (silent and filled intervals) for detecting changes in stimuli of similar duration. RESULTS: Patients produced higher discrimination threshold estimates and smaller amplitude mismatch negativity responses to temporally deviant stimuli. Temporal discrimination thresholds correlated with the amplitude of the phase reversal in mismatch negativity at the left mastoid such that patients who produced the highest thresholds produced the smallest mismatch response. CONCLUSIONS: Imprecise representations of the temporal properties of auditory stimuli can account for some of the reduction in mismatch negativity amplitude in some patients but additional factors clearly contribute. The results suggest that patients who do and do not exhibit temporal processing deficits on behavioural tasks produce different patterns of reduction in duration mismatch negativity.

Duration and frequency mismatch negativity in schizophrenia.

OBJECTIVES: The aim of the present study was to elucidate the reasons for apparent inconsistencies in the schizophrenia literature with respect to the mismatch negativity (MMN) waveform of the event-related potential (ERP). While most previous research has shown that MMN is reduced in schizophrenia, there are a small number of studies reporting that frequency MMN is not reduced. METHODS: We recorded ERPs to auditory stimuli with different frequencies and durations from patients with schizophrenia (N = 14) and control subjects (N = 17) of similar age and sex. MMNs to small but discriminable frequency deviants were contrasted with large frequency deviants and duration deviants. RESULTS: Only the MMN to duration deviants was significantly reduced in patients, although there was evidence of a similar trend for large frequency deviants. CONCLUSIONS: The results together with a review of the frequency MMN literature suggest that there are 3 variables which are important in determining whether patients exhibit a reduced MMN to frequency deviants: deviant probability, degree of deviance and interstimulus interval. The results also indicated that patients with schizophrenia may have particular deficits in processing the temporal properties of auditory stimuli. This finding has implications for the pathophysiology of the disorder as time-dependent processing is reliant on the integrity of an extensive network of brain areas consisting of auditory cortex, areas of pre-frontal cortex, the basal ganglia and cerebellum.

Auditory sensory memory in schizophrenia: inadequate trace formation?

This study explored duration mismatch negativity reductions observed in individuals with schizophrenia, in particular, the relationship to behavioural measures of temporal discrimination and two event-related potential (ERP) components occurring during the first phase of auditory sensory memory. Twenty-two patients with a DSM-IV and ICD-10 diagnosis of schizophrenia and 25 healthy comparison volunteers participated in a behavioural and an ERP testing session. Both groups performed equivalently on behavioural estimates of filled interval duration discrimination and gap detection. In contrast, electrophysiological measures revealed a significant reduction in patients' duration mismatch negativity and a significant difference in patients for the pattern of N100 facilitation over short stimulus onset asynchronies. Whilst behavioural results indicate intact temporal processing of filled intervals and equal temporal resolution limits in schizophrenia, both ERP measures indicated differences in auditory processing that may be traced to activity occurring during the first 250 ms. Results highlight the possibility of abnormalities in the process of auditory trace formation and temporal summation in schizophrenia.

Suicide rates in psychiatric in-patients: an application of record linkage to mental health research.

OBJECTIVE: To study trends in the rate of suicide in psychiatric patients in Western Australia. To examine the associations of suicide with demographic and clinical factors. METHODS: A population-based cohort of 52,010 individuals whose first psychiatric admission occurred in 1980-95 was identified from the Health Services Research Linked Database. There were 471 deaths by suicide by 31 December 1995. Age standardised suicide rates per 1,000 person-years at risk were calculated. Suicide rates in the first year after a patient's first admission were also examined and a proportional hazards regression analysis was performed to examine risk factors for suicide. RESULTS: Male psychiatric patients were 3.4 times more likely to commit suicide than female patients (95% CI 2.76-4.24). Younger patients were at higher risk than older patients, and patients with extended periods of in-patient treatment were at more than double the risk of short-stay patients. Over the 16-year period, the rate of suicide in the first year after first psychiatric admission was found to increase by 3.4% a year (95% CI -0.7-7.6%). CONCLUSIONS: The findings confirm that psychiatric patients are at high risk of suicide. Patient outcomes in terms of risk of suicide after hospital discharge have deteriorated. IMPLICATIONS: Improvements are needed in the provision of community support to high risk psychiatric patients. Further work should be done to identify patients at highest risk of suicide.

Season of birth in schizophrenia and affective psychoses in Western Australia 1916-61.

OBJECTIVE: This study examines seasonality birth effects in schizophrenia and affective psychoses in the southern hemisphere, given possible confounding of age-incidence effects with winter birth peaks in northern hemisphere data. METHOD: Distributions of births by season, quarter and month for individuals born in Western Australia 1916-61 with a diagnosis of schizophrenia (N=2284), affective psychoses (N=3236), and neurotic depression (N=4869) on the statewide mental health register were compared with distributions for the general population. RESULTS: We found no association between season of birth and schizophrenia, affective psychoses or neurotic depression. For schizophrenia, the pattern of risks by quarter reflects northern hemisphere trends. Results by month are difficult to interpret due to large fluctuations in the data. While age-incidence effects had no impact on the distribution of risk, we found an artefactual increase in January births due to routine imputation of missing birth dates. CONCLUSION: Adjusting for artefacts in the data produced a pattern analogous to northern hemisphere trends.

Excess cancer mortality in Western Australian psychiatric patients due to higher case fatality rates.

OBJECTIVE: To investigate the association between mental illness and cancer incidence, mortality and case fatality. METHOD: A population-based record linkage study was undertaken based on 172,932 patients of mental health services in Western Australia. Records of mental health service contacts were linked with cancer registrations and death records. RESULTS: While there was little difference in overall cancer incidence rates between psychiatric patients and the general community (RR in males 1.05, 95%, CI 1.02-1.09, RR in females 1.02, 0.98-1.05), cancer mortality was 39%, higher in males (95%) CI: 32-46%) and 24% higher in females (17-32%). CONCLUSION: People with mental illness in Western Australia do not show an increased incidence rate of cancer, but do have higher cancer mortality. This was attributed to a higher cancer case fatality rate among people with mental illness.

Increasing rates of suicide in Western Australian psychiatric patients: a record linkage study.

OBJECTIVE: To investigate the risk of suicide following contact with mental health services and whether it has changed over time. METHOD: Record linkage was used to obtain the records of previous hospital admissions and mental health service contacts for deaths due to suicide in the period 1980-98. Standardized incidence rates were calculated for the general population and for users of mental health services. Proportional hazards regression was used to assess risk factors within the cohort of people with mental health service contact. RESULTS: Suicide risk was significantly increased in users of mental health services (rate ratio 6.66 in males and 7.52 in females). Suicide risk was highest in the first 7 days after discharge from in-patient care, and decreased exponentially with time since discharge. Suicide risk in users of mental health services has increased over the study period. CONCLUSION: These results highlight the importance of adequate follow-up of patients discharged from in-patient services, and the need for adequate resources for community-based services.

Mortality in Western Australian psychiatric patients.

BACKGROUND: The aim was to examine mortality in psychiatric patients in Western Australia (WA), over a time period of considerable change in the delivery of mental health services. METHODS: A population-based record linkage analysis was undertaken to quantify mortality among people with mental illness in WA. Mortality rates were calculated in users of mental health services and compared with rates in the whole population of WA. Trends in mortality were also examined using relative survival analysis, and proportional hazards regression. RESULTS: The overall mortality rate ratio was 2.57 in males (95% CI: 2.51-2.64), and 2.18 in females (2.12-2.24). The highest cause-specific mortality rate ratio was for deaths due to suicide [RR: 7.37 in males (95% CI: 6.74-8.05) and 8.38 in females (95% CI: 7.11-9.89)], with mortality rate ratios being significantly greater than 1 for all other major causes of death. A relative survival analysis found that the excess mortality risk was concentrated in the first few years after first contact with mental health services. Proportional hazards regression analysis found a slight elevation of mortality rates over time. CONCLUSIONS: Mortality among psychiatric patients remains high and appears to be increasing. Highest excess mortality rate is associated with suicide, but mortality rates are significantly elevated for all major causes of death.

Suicide and attempted suicide among older adults in Western Australia.

BACKGROUND: Suicide rates are high in later life. Risk factors include male sex and depressive illness. This study investigated the relationship between suicidal behaviour and contact with mental health services among the elderly in Western Australia. METHODS: Record linkage was used to obtain records of hospital admissions and mental health service contacts for all suicide attempts and deaths in the period 1980-95. Standardized incidence ratios were calculated for the elderly, general population and people with mental health service contacts. Cox regression was used to evaluated potential risk factors for elderly people who were in contact with mental health services. RESULTS: People over 60 years of age accounted for 15% of suicides and 4.6% of attempted suicides. Suicide rates were 3.3 times higher in males and 4.4 times higher in females when compared to the general population of elderly people. For attempted suicide, the rate was 5.8 times higher in males and 6.6 times higher in females with prior contact with mental health services. Highest risk of suicide was found in patients with diagnoses of affective psychoses (RR = 3.7), adjustment reaction (RR = 3.2) or depressive disorder (RR = 2.8). The diagnosis of cancer was associated with decreased risk of suicide (RR = 3.6) and attempted suicide (RR = 1.9). CONCLUSIONS: Suicide rates are high among the elderly in Western Australia. Suicide is significantly associated with the diagnosis of mood disorder. Suicide attempts are less common, and are associated most strongly with mood and personality disorders. The decreased risk of self-harm behaviour among patients with cancer warrants further investigation.