Sexual Motivation: A Comparative Approach in Vertebrate Species

Sex Differences in Sexual Motivation in Humans and Other Mammals: The Role of Conscious and Unconscious Processes

In self-report questionnaires, men report higher scores than women on variables such as desire for sex, frequency of sexual thoughts, number of sex partners, etc. Based on this, men are considered to have a higher level of sexual motivation than women. However, retrospective self-reports may be unsuitable for estimations of the inherent level of sexual motivation. We review data on automatic (unconsciously controlled) responses and measures of implicit motivation during exposure to sexual stimuli. These responses and measures are inaccessible to willful manipulations and make it possible to determine whether the sex difference in answers to questionnaires is replicated when volitional response manipulations are unlikely. We complement the human data with observations from some rodent and non-human primate species. The attentional resources allotted to stimuli with sexual relevance as well as genital responses to such stimuli are similar in men and women. Measures of implicit motivation also fail to detect any sex difference. Finally, the frequency of masturbation is superior in female infants before the age at which social expectations begin to determine behavior. Neither in rodents nor in non-human primates is there any clear-cut evidence for sex differences in motivation. It seems that males and females are similar with regard to the intensity of sexual motivation. The responses to questionnaires may be affected by social learning of sexual scripts and/or the inferior quality of sexual experiences in women, among other things.

Neurobiology of Pathogen Avoidance and Mate Choice: Current and Future Directions

Animals are under constant threat of parasitic infection. This has influenced the evolution of social behaviour and has strong implications for sexual selection and mate choice. Animals assess the infection status of conspecifics based on various sensory cues, with odours/chemical signals and the olfactory system playing a particularly important role. The detection of chemical cues and subsequent processing of the infection threat that they pose facilitates the expression of disgust, fear, anxiety, and adaptive avoidance behaviours. In this selective review, drawing primarily from rodent studies, the neurobiological mechanisms underlying the detection and assessment of infection status and their relations to mate choice are briefly considered. Firstly, we offer a brief overview of the aspects of mate choice that are relevant to pathogen avoidance. Then, we specifically focus on the olfactory detection of and responses to conspecific cues of parasitic infection, followed by a brief overview of the neurobiological systems underlying the elicitation of disgust and the expression of avoidance of the pathogen threat. Throughout, we focus on current findings and provide suggestions for future directions and research.

Hearing, touching, and multisensory integration during mate choice

Mate choice is a potent generator of diversity and a fundamental pillar for sexual selection and evolution. Mate choice is a multistage affair, where complex sensory information and elaborate actions are used to identify, scrutinize, and evaluate potential mating partners. While widely accepted that communication during mate assessment relies on multimodal cues, most studies investigating the mechanisms controlling this fundamental behavior have restricted their focus to the dominant sensory modality used by the species under examination, such as vision in humans and smell in rodents. However, despite their undeniable importance for the initial recognition, attraction, and approach towards a potential mate, other modalities gain relevance as the interaction progresses, amongst which are touch and audition. In this review, we will: (1) focus on recent findings of how touch and audition can contribute to the evaluation and choice of mating partners, and (2) outline our current knowledge regarding the neuronal circuits processing touch and audition (amongst others) in the context of mate choice and ask (3) how these neural circuits are connected to areas that have been studied in the light of multisensory integration.

Adolescence and Postpartum: Two Life Periods to Deepen Our Understanding of the Complexity of Female Rat Sexual Behavior

The sexual behavior of the female rat has been extensively studied and used as a model for human female sexuality. The development of models that focus on sexual interaction from the female’s perspective has demonstrated the complexity of this behavior, in which motivational and affective aspects have great relevance. This review describes, from a historical perspective, some of the studies that have shed light on this complexity and presents the potential of two periods in the female’s life to expand our understanding of sexual behavior: adolescence and postpartum estrus. Cycling adolescent female rats can express sexual behavior even though some of the underlying circuitry is still developing. Therefore, this is an ideal time for studying the ontogeny of sexual behavior, the interaction of sexual and social motivations, and the neuroendocrine changes that lead to adult behavior. Female rats also show a fertile estrus a few hours after parturition. During this period, rats are simultaneously sexually and maternally motivated, making postpartum estrus an excellent model for exploring the interaction of these two social motivations. What we know so far about female sexual behavior in these unique periods of life reaffirms its richness and shows that much remains to be known.

Understanding the Role of Incentive Salience in Sexual Decision-Making

In the search for understanding female sexual decision-making, progress has been made in uncovering a variety of perceptual biases and most of these concern the animal's sensory biology and cognitive processes. We are now poised to dig deeper into the female's decision-making and ask if incentive salience, which plays a role in all types of appetitive behaviors, also influences a female's "taste for the beautiful." The incentive salience hypothesis suggests that dopamine assigns value or salience to objects or actions. After value is assigned to all potential actions, an action selection system then chooses among potential options to select the most valuable action. In this view, dopamine stimulates reward-seeking behavior by assigning incentive salience to specific behavioral actions, which in turn, increases pursuit and focus on objects or stimuli that represent the valuable action. Here, we apply this framework to understand why females are compelled to respond maximally to some male courtship signals over others and how this process may reveal a female's hidden mate preferences. We examine studies of dopamine and the mesolimbic reward system because these may play a role in expanding the female's perceptual landscape for novelty in male courtship signals and establishing novel hidden preferences. We review three avenues of research that may identify signatures of incentive salience in females during sexual decision-making. This review includes studies of dopamine agonist or antagonist administration in females during mate choice or partner preference tests, measures of neural activity in dopaminergic neural circuits during mate choice or partner preference tests, and social regulation of dopamine in females when entering reproductive contexts and/or exposure to mate signals. By applying the incentive salience hypothesis to female reproductive decision-making, it redefines how we see the female's role in sexual encounters. Females cannot be considered passive during reproductive encounters; rather they are seeking sexual encounters, particularly with males that tap into their perceptual biases and initiate a reward-seeking response. Incentive salience applied to reproductive behavior requires considering females as viewing sexual stimuli as rewarding and initiating action to seek out this reward, all of which indicates females are driving sexual encounters.

The social network: Neural control of sex differences in reproductive behaviors, motivation, and response to social isolation

Social animal species present a vast repertoire of social interactions when encountering conspecifics. Reproduction-related behaviors, such as mating, parental care, and aggression, are some of the most rewarding types of social interactions and are also the most sexually dimorphic ones. This review focuses on rodent species and summarizes recent advances in neuroscience research that link sexually dimorphic reproductive behaviors to sexual dimorphism in their underlying neuronal circuits. Specifically, we present a few possible mechanisms governing sexually-dimorphic behaviors, by hypothalamic and reward-related brain regions. Sex differences in the neural response to social isolation in adulthood are also discussed, as well as future directions for comparative studies with naturally solitary species.

Motivational Drive in Non-copulating and Socially Monogamous Mammals

Motivational drives guide behaviors in animals of different species, including humans. Some of these motivations, like looking for food and water, are crucial for the survival of the individual and hence for the preservation of the species. But there is at least another motivation that is also important for the survival of the species but not for the survival of the individual. Undoubtedly, sexual motivation is important for individuals to find a mate and reproduce, thus ensuring the survival of the species. In species with sexual reproduction, when males find a female in the appropriate hormonal conditions, they will display sexual behavior. However, some healthy males do not mate when they have access to a sexually receptive female, even though they are repeatedly tested. These non-copulating (NC) individuals have been reported in murine, cricetid and ungulates. In humans this sexual orientation is denominated asexuality. Asexual individuals are physically and emotionally healthy men and women without desire for sexual intercourse. Different species have developed a variety of strategies to find a mate and reproduce. Most species of mammals are polygamous; they mate with one or several partners at the same time, as occur in rats, or they can reproduce with different conspecifics throughout their life span. There are also monogamous species that only mate with one partner. One of the most studied socially monogamous species is the Prairie vole. In this species mating or cohabitation for long periods induces the formation of a long-lasting pair bond. Both males and females share the nest, show a preference for their sexual partner, display aggression to other males and females and display parental behavior towards their pups. This broad spectrum of reproductive strategies demonstrates the biological variability of sexual motivation and points out the importance of understanding the neurobiological basis of sexual motivational drives in different species.