According to the author, the biological link between love and anger is found in the Prefrontal Cortex. This part of the brains neural system, which is responsible for <em>rage</em>, shares proximity with the cranial centers that anticipate rewards. The author also posits that winning a beloved one is interpreted as a type of reward by the brain.
The brain, as posited, responds with frustration when love as a stimulus is withdrawn from it. This observation is called the "Frustration-Aggression Hypothesis".