November 02, 2023

The drawers of Stephen Robertson’s office are stuffed with goodies most would find appealing: cookies, potato chips, peanut butter — and a surprising amount of powdered chocolate drink mix. The assistant professor of psychology and one of his students have been using the snacks to study the neurological consequences of chronic consumption of a high-fat, high-sugar diet.

“This involves using rats in two groups: one consuming a regular diet of rat chow, and the other consuming a high-fat, high-sugar diet we make in the lab,” explained Katt Teles ’24, a neuroscience major in the Honors Program.

Using a blender, Teles created what she dubbed “gloop,” a mix of cookies, potato chips and drink mix, that was fed to some of the rats in Susquehanna’s lab. The other group continued receiving a protein-heavy rat food.

After diet exposure, Teles and Robertson trained both groups of rats to respond to a sugar pellet reward that was paired with a light and auditory stimulus. Once they responded to this pairing of visual, auditory and food rewards, “extinction” was enacted at various time points.

Katt Teles '24 makes gloop in the psychology lab. Katt Teles ’24 makes “gloop” in the psychology lab.“This meant temporarily taking away the food reward associated but continuing to present the visual and light stimuli,” Robertson explained. “We observed how the rats’ responses differed based on their diet exposure.”

Preliminary findings show that rats that consumed the high-fat, high-sugar diet were less sensitive to “extinction” conditions. This means that rats exposed to a high-fat, high-sugar diet are more persistent in responding, which is likely being driven by the food-associated light and auditory stimuli. One possible interpretation is that the high-fat, high-sugar diet is altering the rewarding properties of the food cues relative to rats fed a control diet.

“In other words, it would appear that the high-fat, high-sugar diet blunts the brain’s ability to process rewards,” Robertson said.

To draw a parallel to humans, if someone has been consuming a high-fat, high-sugar diet, food-associated stimuli could be encouraging that person to continue that behavior — despite their best attempt to maintain a clean diet.

There is already existing literature that suggests high-fat, high-sugar diets lead to a change in the reward processing of the brain, Robertson said. His greatest interest in his current research is to try to duplicate earlier results through the use of operant chambers. Widely used in behavioral psychology research, an operant chamber is a controlled environment that allows researchers to study behavioral conditioning and modification, usually in animals.

“Although we are researching this particular behavioral phenomenon in animals, we can infer some parallels between the behavior we’re seeing in the lab and how the human brain responds to the same type of diet,” Robertson said. The next step is to use dopaminergic drugs that target the reward centers of the brain as tools to investigate diet-induced changes in neurobiology.

“We are trying to determine if we stimulate dopamine systems will the rat respond more or less to the food-paired stimuli depending on diet exposure,” Robertson said.

It has been an informative experience for Teles, who is from Collegeville, Pennsylvania, and is considering a career in research after graduation.

“I have learned the basics of rat husbandry and care, and I have gained skills in conducting procedures, collecting data and organizing that data in a way that makes it easy to analyze once trials are completed,” Teles said. “Working in the lab has helped me gain vital skills, as I now have experience with animal procedures following ethical and safety guidelines. Outside of lab work, I have gained teamwork, time management and problem-solving skills that are applicable to any potential future career.”

When reflecting on challenges she overcame in the lab, she recalled how the first few batches of the high fat, high-sugar diet she created didn’t work out. They were too thick, causing the food processor to overheat.

“With some trial and error, I figured out that presoaking some of the ingredients in water allows them to soften up and blend with ease,” Teles said. “It may seem trivial, but it made this important part of the process in the lab so much easier.”

Learn more about the Department of Psychology.