In his book “The Great Pheromone Myth,” Richard L. Doty cites the article mentioned below as evidence that visual input activates the hypothalamus. No mammalian pheromones are required; thus, his thesis and book title. In my mammalian model, the direct effect of olfactory/pheromonal input on hypothalamic gonadotropin releasing hormone (GnRH) pulsatility allows for an associated link from visual input to genetically-predisposed sexual preferences that are influenced by the social environment. These preferences are linked to, and probably dependent on, subtle variations in prenatal and postnatal hypothalamic GnRH pulsatility. Postnatal variations are caused by social odors and their direct effect on “The Mind’s Eyes” (i.e., located in the medial preoptic area of the anterior hypothalamus (MPOA/AH). Visual stimuli have do not directly activate the hypothalamus.
If my model is correct, the postnatal social odors that cause subtle variations in GnRH pulsatility also establish the “yuck” factor with regard to sexual preferences in the same neurophysiological manner that food odors establish food preferences. However, information on sex differences in the social odors and sexually differentiated responses to the social odors have greater explanatory power than found in other theories about the biologically based origins of sexual orientation. If my model is not correct, someone should tell me how visual input can activate the hypothalamus in the absence of any association with olfactory/pheromonal input.
Even more on the yuck factor (read the last sentence of the abstract below):
Paul T, Schiffer B, Zwarg T, Krüger TH, Karama S, Schedlowski M, Forsting M, Gizewski ER. (2008). Brain response to visual sexual stimuli in heterosexual and homosexual males. Human Brain Mapping, 29, 726-735.
Although heterosexual and homosexual individuals clearly show differences in subjective response to heterosexual and homosexual sexual stimuli, the neurobiological processes underlying sexual orientation are largely unknown. We addressed the question whether the expected differences in subjective response to visual heterosexual and homosexual stimuli may be reflected in differences in brain activation pattern. Twenty-four healthy male volunteers, 12 heterosexuals and 12 homosexuals, were included in the study. BOLD signal was measured while subjects were viewing erotic videos of heterosexual and homosexual content. SPM02 was used for data analysis. Individual sexual arousal was assessed by subjective rating. As compared to viewing sexually neutral videos, viewing erotic videos led to a brain activation pattern characteristic for sexual arousal in both groups only when subjects were viewing videos of their respective sexual orientation. Particularly, activation in the hypothalamus, a key brain area in sexual function, was correlated with sexual arousal. Conversely, when viewing videos opposite to their sexual orientation both groups showed absent hypothalamic activation. Moreover, the activation pattern found in both groups suggests that stimuli of opposite sexual orientation triggered intense autonomic response and may be perceived, at least to some extent, as aversive.