The initial drive - lust - is brought on by surges of sex hormones, such as testosterone and estrogen. These induce an indiscriminate scramble for physical gratification. Attraction transpires once a more-or-less appropriate object is found (with the right body language and speed and tone of voice) and is tied to a panoply of sleep and eating disorders.
Obsessive thoughts regarding the Loved One and compulsive acts are also common. Perception is distorted as is cognition. "Love is blind" and the lover easily fails the reality test. Falling in love involves the enhanced secretion of b-Phenylethylamine (PEA, or the "love chemical") in the first 2 to 4 years of the relationship. This natural drug creates an euphoric high and helps obscure the failings and shortcomings of the potential mate. Such oblivion - perceiving only the spouse's good sides while discarding her bad ones - is a pathology akin to the primitive psychological defense mechanism known as "splitting". Narcissists - patients suffering from the Narcissistic Personality Disorder - also Idealize romantic or intimate partners. A similar cognitive-emotional impairment is common in many mental health conditions.
Love, in all its phases and manifestations, is an addiction, probably to the various forms of internally secreted norepinephrine, such as the aforementioned amphetamine-like PEA. Love, in other words, is a form of substance abuse. The withdrawal of romantic love has serious mental health repercussions.
Also via Mind Hacks, studies of the neurology of sarcasm, which turns out to be a good subject for exploring subjects' theory of mind, being carried out at the fantastically-named Rambam Medical Center in Haifa, Israel.