Cory Pettit and Michael J. Larson, PhD, Psychology and Neuroscience
The purpose of this study was to examine the effects of exercise on the neural correlates of response inhibition to high and low calorie foods. Specifically, we aimed to explore whether engaging in forty-five minutes of moderate intensity exercise affects brain activity that denotes inhibitory control while a person withholds practiced responses to pictures of high or low calorie food. We quantified inhibitory control by measuring the amplitude of the N2 event related potential (ERP; described below) using electroencephalogram (EEG) technology.
An increasing amount of scientific literature has emphasized the importance of exercise in overall quality of life, prevention of disease, and especially weight loss. A recent study by Philippou et al. (2012) comparing dieting to a regimen of moderate intensity exercise along with dieting found that the combination of exercise and diet more than doubled the amount of weight lost. Moreover, the diet-only group had a 1% decrease in body fat percent while the diet and exercise group had a remarkable decrease of more than 8%. In addition to burning calories, there is evidence that exercise may positively affect eating habits. For example, a previous study conducted by the faculty mentor for this project (Hanlon, Larson, Bailey, & Lecheminant 2012) examining the effects of exercise on the neural response to food stimuli found that there was a decreased neural response to food stimuli following a bout of moderate exercise. No studies to date, however, have looked at the effects of exercise on inhibitory control of food-related stimuli. We hypothesized that exercise may help one to display inhibitory control towards food. We tested this hypothesis by examining neural indices of response inhibition towards high and low calorie foods following sedentary activities and following moderate intensity exercise.
Electroencephalogram (EEG) technology allows us to visualize brain activity by viewing event related potentials (ERP). The ERP is an electrical measurement of the brain’s reaction to a stimulus, and appears on the EEG readout as a time-locked waveform. We will focus on the N2 component, a portion of the ERP waveform that has been implicated in inhibitory control (Mueller, Swainson, & Jackson 2009). N2 amplitudes are greater when there is an increased need for inhibitory control. Thus, we expect that after exercise, there will be a greater increase in N2 amplitude when participants are required to inhibit responses to high calorie foods compared to low calorie foods.
Thirty seven participants (8 obese) completed the study (average age=28.3 years, SD=10.8). All participants completed two study sessions, one where the EEG task was preceded by exercise and one where the EEG task was preceded by non-physical measurements (e.g., sitting and completing questionnaires). Condition order was randomly assigned. In the non-exercise condition, we measured the participants’ height and BMI, as well as administered a survey. They then proceeded to the EEG task. In the exercise condition, instead of a body composition assessment, participants exercised on a treadmill at 3.8mph, 0% grade for 45 consecutive minutes before advancing to the EEG portion. Participants completed a go/no-go task using pictures of food for the stimuli. The pictures were classified as high or low calorie, as designated by Killgore et al. (2013). A smaller N2 amplitude indicates that a person had less inhibitory control towards the food stimulus while a larger N2 amplitude shows they had greater inhibitory control.
In the go/no-go task, participants responded when they saw a certain stimulus (the go trial) and withheld their response when they see a different response (the no go trial). One task had the high-calorie food as the go stimulus, and the other had the low calorie food appear as the no go trial. The statistical analysis consisted of a 2-Group (obese, normal weight) x 2-Exercise (exercise, non-exercise) x 2-Food Type (high calorie, low calorie) repeated measures ANOVA. Multiple regression analysis were also be done utilizing demographics and N2 amplitude to predict caloric intake.
We found that the go/no-go protocol was effective in inducing inhibitory control, as the N2 amplitude in the no-go trials was significantly larger than that of the go trials (p<.05). A main effect of exercise was also found, in that the difference in N2 amplitude between the no-go and go trials was significantly larger when the task was preceded by exercise than the sedentary activity (p<.05). No significant difference was found between the N2 amplitudes of the obese and lean participants, or between the high and low calorie trials (p>.05). In addition, no significant correlations or regression predictions were found between N2 amplitudes and actual calories consumed.
The larger difference in N2 amplitude after exercise than after sitting/completing questionnaires implies that exercise increased the inhibitory response during the go/no-go task, as we hypothesized. The difference between the obese and lean groups was trending in the right direction, but was not significant. The same trend was seen in the interaction between high and low calorie tasks. The study is currently very underpowered, with only 29 lean participants and 8 obese participants. We believe that as we approach out goal of 50 lean participants and 50 obese, these interactions may become significant.
Our hypothesis that exercise would increase the inhibitory control response was confirmed, as demonstrated by the larger N2 amplitude. Our hypotheses that obese individuals would have a decreased inhibitory control response, and that there would be a decreased inhibitory control response to high calorie foods were not confirmed by these preliminary results.
Hanlon B., Larson M., Bailey B., & Lecheminant J. (2012). Neural response to pictures of food after exercise in normal-weight and obese women. Medicine & Science in Sports & Exercise. 44, 1864-1870.
Kilgore, W.D.S., Young, A.D., Femia, L.A., Bogorodzki, P., Rogowska, J. & Yurgelun-Todd, D.A. (2003). Cortical and limbic activation during viewing of high- versus low-calorie foods. Neuroimage. 19, 1381-1394.
Mueller SC., Swainson R., & Jackson GM. (2009). ERP indices of persisting and current inhibitory control: a study of saccadic task switching. Neuroimage. 45, 191-197.
Philippou C., Andreou E., Menelaou N., Hajigeorgiou, P., Papandreou, D. (2012). Effects of diet and exercise in 337 overweight/obese adults. Hippokratia. 16. 46-50.