How Good Chocolate Tastes: Eyes Reveal Pleasure Response

How good does that chocolate taste? Apparently, it's easy to tell--just look at the eyes. Scientists have discovered that the brain's pleasure response to tasting food can be measured through the eyes using a common, low-cost ophthalmological tool.

Dopamine is associated with a variety of pleasure-related effects in the brain. It's a simple organic chemical that plays an important role in motor control, motivation, arousal, cognition and reward. In the eye's retina, dopamine is released when the optical nerve activates in response to light exposure. Yet in order to see if this chemical could be measured in response to food, the researchers had to turn to a new technique--electroretinography (ERG)

Nine participants without eating disorders were asked to fast for four hours. They were then given a small piece of brownie, which was placed in their mouths. The researchers then tested the neurotransmitter dopamine in the retina with ERG. Surprisingly, they found that electrical signals in the retina spiked high in response to a flash of light.

How high was it? The participants were also given the stimulant drug methylphenidate to induce a strong dopamine response. The levels measured with the brownie were just as high as the ones seen with the methylphenidate.

"What makes this so exciting is that the eye's dopamine system was considered separate from the rest of the brain's dopamine system," said Jennifer Nasser, an associate professor in the department of Nutrition Sciences at Drexel University, in a news 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 eyes dopamine system."

There are a few issues with the study, though. It's only a small-scale demonstration of the concept, which means that more research needs to be done before the technique is validated. But if it is, then it means that other researchers could use ERG for studies of food addiction and food science.

"My research takes a pharmacology approach to the brain's response to food," said Nasser. "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. We need more user-friendly tools to do that."

The findings are published in the journal Obesity.