In this theoretical review, we begin by discussing brains and minds from a dynamical systems perspective, and then go on to describe methods for characterizing the flexibility of dynamic networks. We discuss how varying degrees and kinds of flexibility may be adaptive (or maladaptive) in different contexts, specifically focusing on measures related to either more disjoint or cohesive dynamics. While disjointed flexibility may be useful for assessing neural entropy, cohesive flexibility may potentially serve as a proxy for self-organized criticality as a fundamental property enabling adaptive behavior in complex systems. Particular attention is given to recent studies in which flexibility methods have been used to investigate neurological and cognitive maturation, as well as the breakdown of conscious processing under varying levels of anesthesia. We further discuss how these findings and methods might be contextualized within the Free Energy Principle as a fundamental principle of brain organization, and describe potential methodological advances from this paradigm. Finally, with relevance to computational psychiatry, we propose a research program for obtaining a better understanding of ways that dynamic networks may relate to different forms of psychological flexibility, which may be the single most important factor for ensuring human flourishing.

Is sexual orientation an evolutionary adaptation or social construct? With respect to sexual preferences, to what extent are we “born that way” and to what extent does learning matter? This chapter discusses how nature and nurture may interact to shape sexual motivation by reviewing existing literature on sexual preferences and orientations, as well as by considering sex/gender differences in erotic plasticity, sexual fluidity, and the specificity of sexual arousal. We describe how these phenomena might be accounted for by processes in which mind body feedback loops amplify some sexual responses over others on multiple levels, which we refer to as the Reward Competition Feedback (RCF) model. With respect to sex/gender differences, we describe how these positive feedback processes might be amplified in men compared with women, potentially substantially driven by differences in the constraints and affordances of female and male anatomy. More specifically, we argue that the well-known female-male difference in the concordance of genital and subjective arousal may contribute to well-known differences in sexual specificity and plasticity/fluidity. We further provide convergent support for RCF by reviewing preexisting theories of sexual learning. Finally, we consider some of the ethical implications of models in which sexual orientation might be shaped by experiences over the course of development.

A small number of studies have examined neuroanatomical differences between heterosexual and homosexual men and women. These studies have yielded mixed support for the hypothesis that homosexual individuals possess sex-atypical neural anatomy. However, in addition to differing along dimensions of sex-typicality, non-heterosexual individuals’ brains may be different in other ways, potentially as a result of differences in experience. One way in which sexual minorities may differ from others is in their social experiences. Bisexual individuals in particular may occupy unique social niches and experience complex social environments as a result of sexual and romantic interactions with both men and women, and potentially also in terms of having a less-widely-recognized sexual identity than heterosexual and homosexual individuals. Based on this idea, we hypothesized that bisexual individuals may show increased gray matter volume and activity in two social-cognition-related areas of the brain: the right temporoparietal junction (rTPJ) and the dorsomedial prefrontal cortex (dmPFC). Contrary to our hypotheses, neither brain structure nor brain activity in the rTPJ and dmPFC were significantly greater in bisexual individuals than in heterosexual and homosexual individuals. Instead, we found larger rTPJ volumes in heterosexual women than in homosexual women. We also found larger relative volumes in the dmPFC in women than in men, consistent with a recent large-scale study of sex differences, and potentially indicative of sex and gender differences in social cognition.

In this study, we attempted to replicate past work focusing on differences in neuroanatomical structures between heterosexual and homosexual men and women. We also performed the first analyses of sexual orientation and neuroanatomy to include bisexual men and women. Sex differences in raw subcortical volumes were consistent with past work and a broader literature on sex differences, showing larger raw subcortical volumes in male groups than female groups. However, we did not confirm past findings showing larger raw volumes in heterosexual than in homosexual men in the left thalamus or right thalamus. Additionally, we did not confirm past findings showing thicker cortices in heterosexual men than in homosexual men in visual/occipital areas (right cuneus, right lingual gyrus, right pericalcarine cortex) or a frontal area (right pars triangularis). Exploratory whole-brain analyses revealed several areas of difference between women that may be of interest for future confirmatory research. Bisexual women had smaller volumes in a region of the olfactory tubercule than heterosexual women as well as a thicker right anterior insula region than homosexual women. Homosexual women had smaller volumes in regions of the inferior parietal lobule (IPL) than both heterosexual women and bisexual women. The functional relevance of these brain areas in terms of understanding female sexual orientation is unclear. However, based on these areas, future work may wish to consider the potential social, emotional, attentional, interoceptive, or general reward-related characteristics that may differentiate women with different attraction patterns. In contrast to previous work, no differences were found between groups of men (heterosexual, bisexual, or homosexual) in any of our analyses. Finally, in terms of whole-brain analyses of sex differences, heterosexual women had both thicker cortices and larger (relative to the whole brain) gray matter volume than heterosexual men in the superior frontal gyrus, in contrast to large-scale studies of sex difference. Although statistically significant at a stringent threshold (FWE-corrected), our whole-brain findings should be interpreted and generalized with caution. The heterogeneity of patterns across analyses of sexual orientation and brain structure (and even across studies of sex/gender and brain structure) suggests that findings may potentially depend upon particular sample characteristics, and potentially Type 1 error due to the testing of many different brain areas.