Differential effects of negative emotion on memory for items and associations, and their relationship to intrusive imagery.

A crucial aspect of episodic memory formation is the way in which our experiences are stored within a coherent spatio-temporal context. We review research that highlights how the experience of a negative event can alter memory encoding in a complex manner, strengthening negative items but weakening associations with other items and the surrounding context. Recent evidence suggests that these opposing effects can occur through amygdala up-modulation to facilitate item encoding, while the hippocampal provision of contextual binding is down-modulated. We consider how these characteristics of memory for negative events might contribute to the development and maintenance of distressing intrusive imagery in posttraumatic stress disorder, and how they should influence therapeutic interventions.

Nitrous oxide speeds the reduction of distressing intrusive memories in an experimental model of psychological trauma.

BACKGROUND: Post-traumatic stress disorder (PTSD) involves maladaptive long-term memory formation which underlies involuntary intrusive thoughts about the trauma. Preventing the development of such maladaptive memory is a key aim in preventing the development of PTSD. We examined whether the N-methyl d-aspartate receptor (NMDAR) antagonist gas nitrous oxide (N2O) could reduce the frequency of intrusive memories by inhibiting NMDAR-dependent memory consolidation in a laboratory analogue of psychological trauma. METHOD: Participants were randomized to inhale N2O (N = 25) or medical air (N = 25) after viewing a negatively valenced emotional film clip ('trauma film'). Participants subsequently completed a daily diary assessing frequency of intrusive thoughts relating to the film clip. A week later, participants completed an explicit memory recall task related to the film. RESULTS: Post-encoding N2O sped the reduction in intrusive memory frequency, with a significant reduction by the next day in the N2O group compared to 4 days later in the air group. N2O also interacted with post-film dissociation, producing increased intrusion frequency in those who were highly dissociated at baseline. Sleep length and quality the night after viewing the film did not differ between the groups. CONCLUSION: N2O speeds the reduction of intrusive analogue trauma memory in a time-dependent manner, consistent with sleep-dependent long-term consolidation disruption. Further research with this drug is warranted to determine its potential to inoculate against enduring effects of psychological trauma; however, caution is also urged in dissociated individuals where N2O may aggravate PTSD-like symptomatology.

Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry.

AIMS: To update the analysis of the cohort mortality and cancer incidence study of employees in the Australian petroleum industry. METHODS: Employees from 1981 to 1996 were traced through the Australian National Death Index and the National Cancer Statistics Clearing House. Cause specific mortality and cancer incidence were compared with those of the Australian population by means of standardised mortality ratios (SMRs) and standardised incidence ratios (SIRs). Associations between increased incidence of specific cancers and employment in the petroleum industry were tested by trends according to period of first employment, duration of employment, latency, and hydrocarbon exposure, adjusting for personal smoking history where appropriate. Total follow up time was 176 598 person-years for males and 10 253 person-years for females. RESULTS: A total of 692 of the 15 957 male subjects, and 16 of the 1206 female subjects had died by the cut off date, 31 December 1996. In males, the all-cause SMR and the SMRs for all major disease categories were significantly below unity. There was a non-significant increase of the all-cancer SIR (1.04, 95% CI 0.97 to 1.11). There was a significant increase of the incidence of melanoma (SIR 1.54, 95% CI 1.30 to 1.81), bladder cancer (SIR 1.37, 95% CI 1.00 to 1.83), and prostate cancer (SIR 1.19, 95% CI 1.00 to 1.40), and a marginally significant excess of pleural mesothelioma (SIR 1.80, 95% CI 0.90 to 3.22), leukaemia (SIR 1.39, 95%CI 0.91 to 2.02), and multiple myeloma (SIR 1.72, 95% CI 0.96 to 2.84). CONCLUSIONS: Most cases of mesothelioma are probably related to past exposure to asbestos in refineries. The melanoma excess may be the result of early diagnosis. The excess bladder cancer has not been observed previously in this industry and is not readily explained. The divergence between cancer incidence and cancer mortality suggests that the "healthy worker effect" may be related to early reporting of curable cancers, leading to increased likelihood of cure and prolonged mean survival time.

Validation of exposure estimation for benzene in the Australian petroleum industry.

A nested case-control study was undertaken to investigate whether an excess of lympho-haematopoietic cancers in the Australian petroleum industry was associated with benzene exposure. The benzene exposures of the cases and controls were estimated using a quantitative algorithm based largely on exposures measured in the Australian petroleum industry. The algorithm was used to estimate, for each subject, the benzene exposure in parts per million (ppm) for each job held in the industry, and the cumulative exposure in ppm years. Because of the critical importance of the exposure assessment in this design of epidemiological study, particular attention was paid to the reliability of the inputs to the algorithm. The inputs [base estimates (BEs) of exposure and technology-specific exposure modifiers (EMs)] were compared to data from other sources including the occupational hygiene literature. Where such comparison data were available, they were generally found to confirm the values used in the algorithm, although four input values were changed as a result of the validation exercise. The integrity of the task-based algorithm was validated by employing it to calculate the exposures of the tanker drivers in the study and comparing these with measured daily exposure for tanker drivers in the Australian petroleum industry and exposure values found in the occupational hygiene literature. After adjustment for the mix of products carried by the Australian tanker drivers, the estimates from the algorithm were found to be comparable to the measured and literature values. This exercise provided evidence that the exposure assessment for the epidemiological study was reliable and that the results of the study can be used as the basis for evaluating the relationship between exposure to benzene and the risk of lympho-haematopoietic cancer.

Retrospective exposure assessment for benzene in the Australian petroleum industry.

An excess of lympho-haematopoietic (LH) cancers has been identified in the Australian petroleum industry through the Health Watch surveillance programme. A nested case-control study is being conducted to investigate this excess. This paper describes the methods used to provide quantitative estimates of benzene exposure for each of the subjects in the case-control study. Job histories were compiled for each subject from interviews and company employment records. Site visits and telephone interviews were used to identify the tasks included in each job title. Details about the tasks such as their frequency, the technology in use and about changes that had taken place over the years were also gathered. Exposure dated back to the late 1940s for a few subjects. Collaborating petroleum companies provided recent benzene exposure monitoring data. These were used to generate Base Estimates of exposure for each task, augmented with data from the literature where necessary. Past exposures were estimated from the Base Estimates by means of an exposure algorithm. The modifying effects of technological changes and changes to the product were used in the algorithm. The algorithm was then computed to give, for each job, for each subject, an estimate of average benzene exposure in ppm in the workplace atmosphere (Workplace Estimate). This value was multiplied by the years for which the job was held and these values summed to give an estimate of Cumulative Estimate of benzene in ppm-years. The occupational hygienists performing the exposure assessment did so without knowledge of the case or control status of subjects. Overall exposures to benzene in the Australian petroleum industry were low, and virtually all activities and jobs were below a time-weighted average of 5 ppm. Exposures in terminals were generally higher than at refineries. Exposures in upstream areas were extremely low. Estimates of Cumulative Estimate to benzene ranged from 0.005 to 50.9 ppm-years.

Absorption of lead and carbon monoxide in Sydney traffic policemen.

Examination of traffic policemen in Sydney showed that those exposed to motor vehicle emissions had blood lead levels within normal limits but marginally higher than those unexposed. Carboxyhaemoglobin levels depended only on cigarette smoking and were unrelated to exposure to motor vehicle emmissions.

An unusual presentation of systemic organophosphate poisoning.

A man presenting with an acute skin reaction to a pesticide was found to have severe systemic organophosphate poisoning.