[Thor]

As an example of MRI tracking sexual stimuli, men react much more to visual than women, which has been a long standing idea in this field.

http://www.nature.com/neuro/journal/...ll/nn1208.html

Men are generally more interested in and responsive to visual sexually arousing stimuli than are women. Here we used functional magnetic resonance imaging (fMRI) to show that the amygdala and hypothalamus are more strongly activated in men than in women when viewing identical sexual stimuli. This was true even when women reported greater arousal. Sex differences were specific to the sexual nature of the stimuli, were restricted primarily to limbic regions, and were larger in the left amygdala than the right amygdala. Men and women showed similar activation patterns across multiple brain regions, including ventral striatal regions involved in reward. Our findings indicate that the amygdala mediates sex differences in responsiveness to appetitive and biologically salient stimuli; the human amygdala may also mediate the reportedly greater role of visual stimuli in male sexual behavior, paralleling prior animal findings.

Sexual fantasies and the differences between men and women:

http://www.tandfonline.com/doi/abs/1...9#.VAWeGvl_seE

The nature and frequency of men's and women's sexual fantasies were investigated by surveying 307 students (182 females, 125 males) at a California state university or junior college via a paper‐and‐pencil questionnaire. The questionnnaire was inspired by modern evolutionary theory and was designed to investigate sex differences in sexual fantasies. Substantial sex differences were found in the salience of visual images, touching, context, personalization, emotion, partner variety, partner response, fantasizer response, and inward versus outward focus. These data, the scientific literature on sexual fantasy, the historically‐stable contrasts between male‐oriented pornography and female‐oriented romance novels, the ethnographic record of human sexuality, and the ineluctable implications of an evolutionary perspective on our species, taken together, imply the existence of profound sex differences in sexual psychologies.

Also this article was interesting, based on an original book discussing what internet searches teaches us about male sexuality, recommend both readings. The original book is linked in this article below (A Billion Wicked Thoughts: What the World’s Largest Experiment Reveals About Human Desire)

http://www.psychologytoday.com/blog/...-sexual-desire

Through millions of anonymous Internet searches, men have repeatedly divulged some rather curious sexual interests. Exploring at length this most bountiful subject of human sexual desire, I’ve already discussed several of them. In this particular post, I’d like to focus on certain erotic predilections that most people would agree slip into the realm of the forbidden. And rightly or wrongly, such preferences are likely to be seen not as erotic but pornographic.
As in most things, there’s clearly a continuum operating here. Males’ most common X-rated computer searches are for youth. And although this preference may be a bit disconcerting, it hardly warrants being seen as perverted (as I’ve sought to explain earlier). Nor does men’s secondary, but substantial, interest in fifty-year-old women (which I’ve also attempted, rationally, to account for). But as we move farther out on the continuum — as we did in my last post, discussing heterosexual men’s attraction to transsexual porn — more eyes can be expected to roll ... or eyebrows to rise.