Histamine originates in cells near the hypothalamus. Histamine helps to increase brain metabolism, making it easier to concentrate. That’s one reason antihistamines, such as Benadryl, that block histamine’s actions can cause sleepiness and make it difficult to stay attentive and to focus. (Guiffre, Kenneth, MD, with Theresa Foy DiGeronimo. The Care and Feeding of Your Brain. p 30-32. NJ: Career Press, 1999.)

Mirror neurons play a key role in sexual response and may play a role in homophobia. When people see sexually aroused genitals of thepreferred sex (e.g., opposite for heterosexuals, same for homosexuals), the brain's mirror neurons and reward centers fire. So when a heterosexual male sees two other men in sexual acts, he can't help but experience it in his mind's body, even if it is at a subconscious level. For the straight male, this is unappetizing and may make a live-and-let-live attitude more difficult to adopt. (Blakeslee, Sandra, and Matthew Blakeslee. The Body Has a Mind of Its Own. p 178-179. NY: Random House, 2008.)