The brain signature and genetic basis of handedness are unclear. Wiberg et al. show that left-handers have higher functional connectivity between language networks, and identify four genomic regions associated with handedness. Variants within these regions appear, by influencing brain architecture, to predispose both to left-handedness and to certain neuropsychiatric diseases.

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The interaction between the brain and the gut has been recognized for many centuries. This bidirectional interaction occurs via neural, immunological and hormonal routes, and is important not only in normal gastrointestinal function but also plays a significant role in shaping higher cognitive function such as our feelings and our subconscious decision-making. Therefore, it remains unsurprising that perturbations in normal signalling have been associated with a multitude of disorders, including inflammatory and functional gastrointestinal disorders, and eating disorders.

Background The use of nipple‐sparing mastectomy (NSM) is increasing, despite unproven oncological safety in the therapeutic setting. The aim of this systematic review was to determine the safety and efficacy of NSM compared with skin‐sparing mastectomy (SSM). Methods A literature search of all original studies including RCTs, cohort studies and case–control studies comparing women undergoing therapeutic NSM or SSM for breast cancer was undertaken. Primary outcomes were oncological outcomes; secondary outcomes were clinical, aesthetic, patient‐reported and quality‐of‐life outcomes. Data analysis was undertaken to explore the relationship between NSM and SSM, and preselected outcomes. Heterogeneity was assessed using the Cochrane tests. Results A total of 690 articles were identified, of which 14 were included. There was no statistically significant difference in 5‐year disease‐free survival and mortality for NSM and SSM groups, where data were available. Local recurrence rates were also similar for NSM and SSM (3·9 versus 3·3 per cent respectively; P = 0·45). NSM had a partial or complete nipple necrosis rate of 15·0 per cent, and a higher complication rate than SSM (22·6 versus 14·0 per cent respectively). The higher overall complication rate was due to the rate of nipple necrosis in the NSM group (15·0 per cent). Conclusion In carefully selected cases, NSM is a viable choice for women with breast cancer who need to have a mastectomy. More research is needed to help further refine which surgical approaches to NSM optimize outcomes.