Role of Dopamine D2 Receptors in Human Reinforcement Learning

Influential neurocomputational models emphasize dopamine (DA) as an electrophysiological and neurochemical correlate of reinforcement learning. However, evidence of a specific causal role of DA receptors in learning has been less forthcoming, especially in humans. Here we combine, in a between-subjects design, administration of a high dose of the selective DA D2/3-receptor antagonist sulpiride with genetic analysis of the DA D2 receptor in a behavioral study of reinforcement learning in a sample of 78 healthy male volunteers. In contrast to predictions of prevailing models emphasizing DA's pivotal role in learning via prediction errors, we found that sulpiride did not disrupt learning, but rather induced profound impairments in choice performance. The disruption was selective for stimuli indicating reward, while loss avoidance performance was unaffected. Effects were driven by volunteers with higher serum levels of the drug, and in those with genetically-determined lower density of striatal DA D2 receptors. This is the clearest demonstration to date for a causal modulatory role of the DA D2 receptor in choice performance that might be distinct from learning. Our findings challenge current reward prediction error models of reinforcement learning, and suggest that classical animal models emphasizing a role of postsynaptic DA D2 receptors in motivational aspects of reinforcement learning may apply to humans as well.Neuropsychopharmacology accepted article peview online, 09 April 2014; doi:10.1038/npp.2014.84

The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015

BackgroundChanging population-level exposure to modifiable risk factors is a key driver of changing cancer incidence. Understanding these changes is therefore vital when prioritising risk-reduction policies, in order to have the biggest impact on reducing cancer incidence. UK figures on the number of risk factor-attributable cancers are updated here to reflect changing behaviour as assessed in representative national surveys, and new epidemiological evidence. Figures are also presented by UK constituent country because prevalence of risk factor exposure varies between them.Methods Population attributable fractions (PAFs) were calculated for combinations of risk factor and cancer type with sufficient/convincing evidence of a causal association. Relative risks (RRs) were drawn from meta-analyses of cohort studies where possible. Prevalence of exposure to risk factors was obtained from nationally-representative population surveys. Cancer incidence data for 2015 was sourced from national data releases and, where needed, personal communications. PAF calculations were stratified by age, sex and risk factor exposure level and then combined to create summary PAFs by cancer type, sex and country.ResultsNearly four in ten (37.7%) cancer cases in 2015 in the UK were attributable to known risk factors. The proportion was around two percentage points higher in UK males (38.6%) than in UK females (36.8%). Comparing UK countries, the attributable proportion was highest in Scotland (41.5% for persons) and lowest in England (37.3% for persons). Tobacco smoking contributed by far the largest proportion of attributable cancer cases, followed by overweight/obesity, accounting for 15.1% and 6.3% respectively of all cases in the UK in 2015. For 10 cancer types, including two of the five most common cancer types in the UK (lung cancer and melanoma skin cancer), more than 70% of UK cancer cases were attributable to known risk factors.ConclusionTobacco and overweight/obesity remain the top contributors of attributable cancer cases. Tobacco smoking has the highest PAF because it greatly increases cancer risk and has a large number of cancer types associated with it. Overweight/obesity has the second-highest PAF because it affects a high proportion of the UK population and is also linked with many cancer types. Public health policy may seek to mitigate the level of harm associated with exposure, or reduce exposure levels – both approaches may effectively impact cancer incidence.Differences in PAFs between countries and sexes are primarily due to varying prevalence of exposure to risk factors, and varying proportions of specific cancer types. This variation in turn is affected by socio-demographic differences which drive differences in exposure to theoretically avoidable ‘lifestyle’ factors. PAFs at UK country level have not been available previously and they should be used by policymakers in devolved nations. PAFs are estimates based on the best available data, limitations in those data would generally bias toward underestimation of PAFs. Regular collection of risk factor exposure prevalence data which corresponds with epidemiological evidence is vital for analyses like this and should remain a priority for the UK Government and devolved Administrations. Keywords: cancer; risk factors; population attributable fractions; UK; tobacco; obesity; lifestyle; environmental<br/

Fatal prostate cancer incidence trends in the United States and England by race, stage, and treatment

Background: Differential uptake of prostate-specific antigen testing in the US and UK has been linked to between-country differences for prostate cancer incidence. We examined stage-specific fatal prostate cancer incidence trends in the US and England, by treatment and race/ethnicity. Methods: Using data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results program and Public Health England’s National Cancer Registration and Analysis Service, we identified prostate cancer patients diagnosed between 1995 and 2005, aged 45–84 years. Fatal prostate cancer was defined as death attributed to the disease within 10 years of diagnosis. We used age–period–cohort models to assess trends in fatal prostate cancer incidence. Results: Fatal prostate cancer incidence declined in the US by −7.5% each year and increased in England by 7.7% annually. These trends were primarily driven by locoregional disease in the US and distant disease in England. Black men in both countries had twofold to threefold higher fatal prostate cancer incidence rates, when compared with their white counterparts; however, receipt of radical prostatectomy lessened this disparity. Conclusions: We report a significant increasing rate of fatal prostate cancer incidence among English men. The black–white racial disparity appears pervasive but is attenuated among those who received radical prostatectomy in the US