"Are unattractive women particularly attracted to neuroscience? Are beautiful women particularly uninterested in the brain?"
Not sure how to answer that, but perhaps we can address why more women, in total, aren't attracted to neuroscience: one reason could be that they're concerned they're not going to be judged solely on the quality of their ideas, presentations, posters, or publications, that some asshole will say to them, "Excellent controls, brilliant experiments: but you really should wear more makeup, smile, and wear a tighter shirt. That is what is really important: for women to look pretty for men's enjoyment."
Now, you might say that I am now attacking a straw man: that even you would never actually go up to a woman as an individual and tell her that she wasn’t pretty enough, recognizing that such comments are neither kind nor productive. But the fact of the matter is that when you post such comments to facebook, you are, in effect, broadcasting them not just to the individuals you had in mind when you wrote the comments, but also to any young woman in science who happens across your facebook page, or the story on Jezebel, or the link from the Association for Women in Science. You were, in fact, addressing the entire world, including all of the graduate students and post-docs attending that conference who, in addition to thinking about questions to ask after the seminars they’ve attended, and the next experiments they want to do based on what they just learned from someone’s poster, now also stop and think: wait, am I not pretty enough?
If it were just you, it really wouldn’t be a problem. But the fact is, it’s not just you. Nor is it just the professor at a proteolysis seminar I recently attended who made a joke about cleavage. These are but tiny components that, in aggregate, contribute to a much larger culture that judges women not just on their science, but also their sexual appeal, and that is one of the factors contributing to one of the greatest challenges to our field, the mass exodus of women from academic science between the postdoctoral level and the assistant professor level, as they leave one line of work that is hostile to them and seek out others that appreciate them more. (Just yesterday I met (yet another) former biochemist who is now a stay-at-home mom.)
You can argue that women shouldn’t care what assholes think of them, precisely because they’re assholes, and that if something as small as a mildly offensive facebook post is enough to make you quit science, then your passion for your work must not be very great. That sentiment is not without merit, but rightly or wrongly, the sexually hostile environment is going to exert a pressure that causes people to leave. In fact, it might provide exactly the kind of selective pressure that then leads to the phenomenon you observe: the sexually hostile environment will enrich for people who don’t care whether other people think they’re pretty or not, and might also cause attractive young women to play down their attractiveness because giving a poster is difficult enough without also having to deal with creepy older guys coming up and hitting on you.