If the eyes are the window into the soul, then recently a group of scientists have found a way to get a better glimpse of the soul and what they have seen may revolutionize our understanding of why people become obese, why they gamble, who will abuse drugs, and who will get Parkinson’s disease or schizophrenia. These scientists, using an inexpensive and non-invasive method, have witnessed the workings of the neurotransmitter dopamine by simply looking into the eyes.

Electroretinography is a well-established, inexpensive and widely available ophthalmologic tool.  A patient stares into a machine that flashes a brief light into the eye and then it monitors the response of the retina at the back of the eye.  The retina is an extension of the brain and is composed of neurons in a complex network that initiates the process of vision.  In response to a flash of light a wave of electrical activity cascades across the retina.  The components of this wave have been given letter names, i.e. a, b, c and d.  The size of one of these waves, the cone b-wave, has been shown to be correlated with how much dopamine is being released into the brain’s reward center deep inside the frontal lobes.

Dopamine is the brain’s reward molecule. Whenever you see or eat tasty food, particularly fat, salt or sugar, your dopamine neurons become very active producing a feeling of euphoria and deep pleasure that encourages you to “do that again!”  These same neurons become very active when people take drugs of abuse, such as meth-amphetamine or cocaine.  They also become active when you have sex or eat chocolate.  All humans really enjoy tickling these neurons into action.

Using electroretinography these scientists were able to monitor via the retina release of dopamine inside the brains of their patients who were given either an amphetamine-like drug or a chocolate brownie to eat.  They reported in the journal Obesity (June, 2013) a highly significant correlation between the size of the b-wave in the retina to oral stimulation with a high sugar/high fat food that was identical to the brains’ response to an amphetamine-like drug.    

Obese people who binge eat may do so because the oral reward they experience from eating fat and sugar rich foods is far greater than non-obese people.  The brains of schizophrenics respond to amphetamine-like drugs with a far greater release of dopamine than do non-schizophrenics.  People who are destined to develop Parkinson’s disease are thought to have fewer dopamine neurons long before their symptoms appear.  Gamblers and people who are drawn to risky sports or other behaviors are thought to have an enhanced dopamine response to these activities.

Using this non-invasive, widely available eye exam to investigate and characterize the brain’s most important reward system might offer health care providers and psychologists the opportunity to intervene and provide preventative treatments before symptoms of these conditions worsen. 

Copyright by Gary L. Wenk, Ph.D., author of Your Brain on Food (Oxford Univ Press)

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