Biological models of love tend to see it as a mammalian drive, similar to hunger or thirst. Psychology sees love as more of a social and cultural phenomenon. There are probably elements of truth in both views — certainly love is influenced by hormones (such as oxytocin), neurotrophins (such as NGF), and pheromones, and how people think and behave in love is influenced by their conceptions of love. The conventional view in biology is that there are two major drives in love — sexual attraction and attachment. Attachment between adults is presumed to work on the same principles that lead an infant to become attached to its mother. The traditional psychological view sees love as being a combination of companionate love and passionate love. Passionate love is intense longing, and is often accompanied by physiological arousal (shortness of breath, rapid heart rate). Companionate love is affection and a feeling of intimacy not accompanied by physiological arousal.
Studies have shown that brain scans of those infatuated by love display a resemblance to those with a mental illness. Love creates activity in the same area of the brain that hunger, thirst, and drug cravings create activity in. New love, therefore, could possibly be more physical than emotional. Over time, this reaction to love mellows, and different areas of the brain are activated, primarily ones involving long-term commitments. Dr. Andrew Newberg, a neuroscientist, suggests that this reaction to love is so similar to that of drugs because without love, humanity would die out. – wiki