Ann M Rogers, MD1, Jianli Wang, MD, PhD2, Robert McHugh2, Qing X Yang, PhD2, Andras Hajnal, MD, PhD2. 1Penn State Hershey Medical Center, 2Penn State College of Medicine
Gastric bypass surgery (GBS) is a commonly performed and substantially successful weight loss procedure. Beyond restriction, malabsorption and gut hormonal changes, GBS appears to change perception of taste and smell, as well as reducing appetite and the appeal of savory meals. There is significant evidence for changes in taste, appetite and satiety after GBS, but little data on the effects on brain reward centers. We used taste-related functional MRI (fMRI) to determine if GBS changes the processing of sensory and hedonic aspects of palatable taste solutions. Based on studies in obese rats and humans demonstrating increased brain activation in reward areas and decreased activation in taste areas, we hypothesized GBS would reverse the alterations in brain areas in response to sweet but not salty tastes compared to pre-surgical activation levels.
With IRB approval and informed consent, fifteen obese subjects were recruited and fourteen finished a baseline preoperative study. Seven subjects were available for re-imaging postoperatively. Subjects fasted twelve hours during the night prior to data acquisition. A gustometer randomly delivered 0.12 ml of a sucrose (0.01 M, 0.3 M or 0.75 M) or sodium chloride (0.01 M, 0.15 M, 0.3 M) taste solution to the anterior portion of the tongue over two separate runs, with an artificial saliva solution (2.5 mM NaHCO3 + 25 mM KCl) as a rinse. Visual cues indicated when to expect a solution delivery, and taste (perception and pleasure) was rated using a response device based on a predefined 4-point-scale. fMRI images of the brain were acquired on a Siemens 3 T system with a blood-oxygen-level-dependent (BOLD) sensitive T2*-weighted EPI sequence. Imaging data was processed in a standard fashion. Activation maps for sweet and salty tastes were generated for each subject and visit. Group analysis of individual subject’s statistical parametric maps was performed using one sample t-tests for the group activation map, and paired t-tests for comparisons of brain activation from taste stimulation before and after surgery.
Significant brain activation was observed for all subjects at each of the three concentrations of sucrose and sodium chloride, in the primary and secondary gustatory cortices and subcortical nuclei. All subjects receiving postoperative examinations had significant weight loss, with mean BMI reduced from 42.5 to 39.4 one month postoperatively, and to 28.5 at one year. Postoperatively, brain activation to sweet taste was significant decreased in the reward system (orbitofrontal cortex), but the response to the salty taste was significantly increased. Significantly increased activation was also observed in the primary gustatory system one year postoperatively, consistent with self-reported increased sensitivity to salty taste from two subjects.
Our fMRI data demonstrated that GBS causes a shift in taste perception and preference after surgery, essentially away from sweet tastes, toward salty tastes. Further study is needed to fully understand the complex brain changes associated with and likely contributing to the success of GBS.