They say that if you look deep into someone's eyes you can see their soul, and while that hasn't been scientifically proven, you can look into someone's eyes and see how pleasurable that last bite of food was. According to a new study, it's possible to see spikes in dopamine levels through a person's eyes when they ingest food.

Dr. Jennifer Nasser, an associate professor in the department of Nutrition Sciences in Drexel University's College of Nursing and Health Professions, found that you could see increases in the retina's dopamine levels using an electroretinogram (ERG), a press release said.

The neurotransmitter dopamine helps control the brain's pleasure and reward systems, however, the dopamine found in the brain was believed to work separately from that found in the eyes' retinas, which act to enhance activity of the cone cells while suppressing rod cells, thereby increasing sensitivity to color and contrast during bright light conditions.

Nasser used a small group of only nine people. Most were overweight with no eating disorders. They fasted for four hours and were then given a small piece of a chocolate brownie. When they put the brownie in their mouths, the ERG flash caught responses from the cones and rods in their eyes. In all participants, electrical signals increased in the same way they did when the participants were given the stimulant drug methylphenidate, which also causes spikes in dopamine. However, there was no reaction when they drank water as a control substance.

"What makes this so exciting is that the eye's dopamine system was considered separate from the rest of the brain's dopamine system," Nasser said in the release. "So most people — and indeed many retinography experts told me this — would say that tasting a food that stimulates the brain's dopamine system wouldn't have an effect on the eye's dopamine system."

Nasser hopes to bring this concept to a larger scale study in order to better understand food addiction and food science.

"My research takes a pharmacology approach to the brain's response to food," she said. "Food is both a nutrient delivery system and a pleasure delivery system, and a 'side effect' is excess calories. I want to maximize the pleasure and nutritional value of food but minimize the side effects."

With dopamine levels rising whenever someone eats, it can be beneficial for studies to look into dopamine responses, especially with obesity on the rise again. According to a survey by the Gallup-Healthways Well-Being Index, obesity has risen in the U.S. to 27.1 percent, compared to 25.5 percent in 2008.