A study noted in telegraph.co.uk in 2009 says that …
“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.”
In case you are wondering, the reverse is not true. In other words, women’s cognitive function does not decrease in the presence of an attractive man.
One hypothesis is that men’s mental resource may have been “used up” trying to impress women.