The serotonin transporter length polymorphism, neuroticism, and depression: a comprehensive assessment of association.

BACKGROUND: A promoter-based length polymorphism (5-HTTLPR) of the human serotonin gene (SLC6A4) has exhibited inconsistent association with emotionality phenotypes, such as major depression (MD) and the personality trait neuroticism (N). Several explanations have been posited to account for this discrepancy, including underpowered experimental design and variation in gender ratio, age, and ethnicity. METHODS: Here, we describe three independent tests of association between the 5-HTTLPR locus and both N and MD in samples selected for extremeness of N-score from two homogenous populations (n = 88,142, and 20,921). Calculations of statistical power indicated that at a 5% alpha level, these samples retain 100% power to detect a genetic effect accounting for just .5% of phenotypic variance. Effects of age were regressed out of the phenotypic measure, and gender was included as a covariate. RESULTS: No statistically significant effects of genotype could be identified on either N or MD phenotypes (in all cases, p > or = .26), independently of the genetic mode of action applied. CONCLUSIONS: Our data do not support the hypothesis that the 5-HTTLPR variant contributes significantly toward human emotionality as indexed by either the Eysenck Personality Questionnaire N scale or the DSM-IV for MD.     

Is accurate self-monitoring necessary for people with acquired neurological problems to benefit from the use of differential reinforcement methods?

Challenging behaviour exhibited by people with acquired neurological problems must be managed if their maximum rehabilitation potential is to be achieved. Differential reinforcement of low rates of responding (DRL) appears to be an effective method for this. The effectiveness of DRL in the presence of severe cognitive deficits, including disorders of attention and memory, is nevertheless surprising. Indeed, such difficulties may prevent individuals with brain injury benefiting from operant conditioning procedures because of impairment of the central executive component of working memory. Consequently, use of other behavioural techniques such as response cost and self-monitoring training (SMT) have been adopted, as it has been argued they circumvent neuropsychological constraints to learning by directing attention to aspects of behaviour not being monitored. DRL, however, may be more desirable as it involves minimal intrusion; is concerned with establishment of pro-social behaviour; and treatment gains can occur rapidly and be maintained for long periods following withdrawal. Whether DRL is dependent upon accurate self-monitoring is addressed through the study of three people participating in rehabilitation. This shows DRL can be effective, despite severe cognitive impairments, but SMT facilitates greater improvements in selective attention. How DRL may circumvent cognitive impairment is discussed.