Reward processing and drug addiction: does sex matter?

Reward processing is crucial to our health and wellbeing and dysfunctional brain reward signaling is a component of a number of psychiatric disorders, including major depression and drug addiction. Rewarding behaviors like eating, parenting, nursing, social play, and sexual activity are powerfully preserved in evolution and are essential for survival. All of them gratifying, they represent enjoyable experiences with high reward values and activate the same brain circuits that mediate the positive reinforcing effects of drugs of abuse. In line with preclinical findings and clinical observations, recent imaging studies confirmed that natural (sex, food) and non-natural (drugs of abuse) rewards differently activate male and female brains (Haase et al., 2011; Wetherill et al., 2014) and also that men and women differ in the ability to resist reward-related impulses (Diekhof et al., 2012). The study of sexual morphological differences in human brain has provided evidence of critical effects of gender on brain architecture and morphometry (Giedd et al., 2012; Feis et al., 2013). Male-female differences in human brain anatomy have stimulated research on the difference in onset, prevalence, and symptomatology of many neuropsychiatric illnesses between women and men, including drug addiction (Rando et al., 2013; Tanabe et al., 2013; Ide et al., 2014). Following the official recognition by International Institutions and Funding Research Agencies on the importance of taking into account potential differences between men and women in all of the relevant aspects of health-related research, gender is receiving increasing attention by medical and scientific communities. As a consequence, evaluation of sex and gender (i.e., biological characteristics and socio-political-cultural influences associated with the terms " male " and " female, " respectively) differences in reward processing in general, and in drug addiction in particular, is increasingly being studied. Numerous human behaviors are driven by evolved instincts and urges. We have evolved the capacity to experience considerable pleasure and happiness from several behaviors, among which are eating, drinking, mating, creating protective shelter, and reproducing, all activating an anatomical and neurochemically defined brain circuit commonly referred to as the " pleasure circuit " or " brain reward system. " In both animals and humans, males and females display diverse attitudes and expectancies, process information differently, perceive experience and emotions in different ways and are behaviorally determined by different needs and drives. Reward processing may also differ between male and female population with sexual hormones playing an important, although not exclusive, role. When looking …