June 25, 2013
Your Eyes May Give You Away And Reveal What Gives You Pleasure
April Flowers for redOrbit.com - Your Universe Online
A new study led by Drexel University has found a common, low-cost ophthalmological tool can measure the brain’s pleasure response to tasting food through the eyes. If the results are validated, this method could have applications for research and clinical work in food addiction and obesity prevention.
The study testing the use of electroretinography (ERG) to indicate increases in the neurotransmitter dopamine in the retina, was led by Dr. Jennifer Nasser, an associate professor in the department of Nutrition Sciences in Drexel University's College of Nursing and Health Professions. The results of this study were published in the journal Obesity.
ERG measures the electrical responses of the different cell types present in the retina, including rods, cones, inner retinal cells, and the ganglion cells. Researchers placed electrodes on the cornea and the skin near the eye, and then exposed the patients’ eyes to stimuli.
A variety of pleasure-related effects in the brain are associated with dopamine, including the expectation of reward. Dopamine is released in the retina of the eye when the optical nerve activates in response to light exposure.
High spikes in the retina’s electrical signals were observed in response to a flash of light when a food stimulus (a small piece of chocolate brownie) was placed in participants' mouths. The spike was as large as that seen when the participants were given the stimulant drug methylphenidate to induce a strong dopamine response. Both responses, to drug and food stimuli, were greater than the response to light observed when the participants ingested a control substance, water.
"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. "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 and her colleagues conducted the study on a very small scale with only nine participants. The majority of the participants were overweight, but none had eating disorders. All nine underwent a four hour fast before food stimulus testing. Larger testing studies are needed to validate the technique. Such validation will allow researchers to use ERG for studies of food addiction and food science.
"My research takes a pharmacology approach to the brain's response to food," Nasser 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. We need more user-friendly tools to do that."
Nasser says the low-cost and ease of performing ERG make it an appealing method for research. For example, Medicare reimbursement for clinical use of ERG is about $150 per session. An ERG session generates approximately 200 scans in just two minutes. A PET scan, on the other hand, costs about $2,000 per session and takes more than an hour to generate a single scan.