Neuroscientist Stephanie Ortigue and psychiatrist Francesco Bianchi-Demicheli use an enhanced EEG to peer into the brains of volunteers looking at pictures of people in swimsuits. The subjects then decide whether each person they were looking at is desirable or not and press a computer key to register their vote.

For more info, read the rest of Carl Zimmer's column on sex in the brain:
discovermagazine.com/2009/october/10-where-does-sex-live-in-brain-from-top-to-bottom