The research shows men who spend even a few minutes in the company of an attractive woman perform less well in tests designed to measure brain function than those who chat to someone they do not find attractive.There is no similar effect of attractive men on women.
Note that this has important implications for things like co-author selection and study group formation. Dan Drezner draws implications for international relations.
Male readers can test the theory using this fine picture of Scarlett Johansson.