Lust originates not in the contours of a shapely calf or a chiseled jaw line, but in the hypothalamus, a nugget of neurons in the brain that's function far outweighs its deceptively diminutive size [source: Fisher]. Situated behind the nose, the hypothalamus directs the pituitary gland to release a range of hormones, including gonadotropin-releasing hormone (GnRH), which has been implicated as a possible human pheromone. The hypothalamus also oversees the production of a class of hormones called androgens. Testosterone, the starring androgen, along with its chemical cousins dihydrotestosterone and androstenedione, sparks sexual arousal and stirs fundamental physical attraction. For men and women alike, higher levels of testosterone coursing through the body correlate to stronger sex drives and, accordingly, more active sex lives [source: HowStuffWorks.com]. No wonder that when lust pans out into kissing contact, testosterone is exchanged in lovers' saliva.
Lust also puts on an impressive show inside the brain. Repeated cognitive studies have found predictable patterns of arousal in the brain in response to titillating images. A functional MRI (fMRI) study conducted in 2002 at the University of Montreal surveyed male and female neurological commotion while viewing pornographic films. A constellation of brain regions lit up, including sites of visual processing, emotional regulation and reward [source: Karama et al]. The specific lust-related neurological hotspots include [source: Patek, Keenan and Shackelford]:
- Anterior cingulate (reward)
- Medial prefrontal cortex (sensory processing)
- Orbitofrontal cortex (decision-making)
- Insula (self-awareness)
- Occipitotemporal cortex (visual processing)
- Amygdala (emotional regulation)
- Ventral striatum (reward)
With all of that excitement in the brain, how do humans possibly stand a chance against lusty urges? Fortunately, the brain is also engineered with a safety valve of sorts. In the early 2000s, when University of Montreal neuroscientist Mario Beauregard asked male study participants to mentally resist arousal in the presence of prurient material, it engaged parts of the prefrontal cortex involved with self-awareness and behavioral regulation [source: Highfield]. The right superior frontal gyrus and right anterior cingulate gyrus, in particular, lent a helping hand to delineate between sexual fantasy and reality. That way, the brain serves as a neurological wingman to help the body stand up against lust.
But when all goes according to plan and initial lust leads to a romantic relationship, when does sexual desire develop into outright love?