Via Pejman Yousefzadeh, this Telegraph (UK) article on scientific investigation of love's effect on the brain is fascinating:
The first intriguing finding is that there is a lot of overlap between the brain areas activated during feelings of romantic love for a partner, and those involved in maternal love for own children. The brain cells implicated are the same as those we know become active whenever an extremely rewarding activity is being undertaken. These are precisely the same neurological locations which are implicated when we consume food and drink we like, take drugs like cocaine, and when we are given monetary rewards. So love is indeed like a drug.However the key result was that it's not just that certain shared areas of the brain are reliably activated in both romantic and maternal love, but also particular locations are deactivated and it's the deactivation which is perhaps most revealing about love.