Lab Spotlight: Brookhaven National Laboratory
Pet Scans Show Brain Responses to Light, Electrical Stimulation

A study measuring metabolic changes in the brains of sighted people is showing similar responses to both light and electrical stimulations. Researchers at the U.S. Department of Energy’s Brookhaven National Laboratory, Doheny Eye Institute at the University of Southern California, and Columbia University now are taking this study a step further to demonstrate that the visual cortex in patients with retinitis pigmentosa (RP) can respond to electrical stimulation.

Using positron emission tomography (PET) scanning and a glucose analogue called FDG, the researchers evaluated and compared what happens to the visual processing part of the brain following different stimuli. Eight healthy volunteers with normal vision participated in the study. Each underwent three PET scans on three different days to represent baseline conditions, responses to light stimulation, and responses to electrical stimulation.

Pet scans showing brain activity in response to light (upper) stimulation and electrical (lower) stimulation. Click on image to enlarge.

Prior to each scan, the volunteers sat quietly in a darkened room for 30 minutes to dark adapt before receiving the FDG injection. For the baseline scan, both eyes were blindfolded. During the light stimulation scan, the person’s right eye was exposed to light flashes from a computer monitor. For the electrical stimulation experiment, a fiber electrode was placed on the right eye and a stream of electrical pulses with the same duty cycle was delivered. The results show similar activation and inactivation patterns between the light and electrical stimulations.

Extending the study to RP patients implanted with retinal prostheses, the researchers will analyze what happens to the visual part of the brain over time as the device is used more by patients. Ultimately, the researchers hope to use the results to examine the effect of cortical reorganization
in retinal degenerative diseases.

The original work was funded by the U.S. Department of Energy, and the RP patient work is being funded by the National Science Foundation (NSF grant number: 0917458).