Background: Bariatric surgery is an effective intervention for morbid obesity, but there is limited understanding of the neuronal mechanisms involved. LAGB is less effective than other procedures for weight loss (Dogan et al. 2014), but unique in that it allows us to test the effects of a restrictive procedure without confounds of malabsorption, and to reverse the band’s action acutely in a double-blind manner. One previous LAGB functional MRI study found decreased activation in paralimbic reward centers and increased activation in cognitive and emotional control regions 12 weeks post-LAGB (Bruce et al., 2012). Studies testing milkshake anticipation and taste found that obese subjects had higher activation in somatosensory, gustatory, and reward regions. (Ng, 2011; Stice, 2008; Bohon, 2009) However no research has yet tested neuronal responses to taste in band adjustment, which may be involved in successful weight loss. We examined neuronal differences using fMRI in LAGB patients who had their band deflated and shamdeflated. Method: Consented patients were 14 adults (MAge1⁄4 42.8 years, SD1⁄49.1; 100% female) who had undergone LAGB at least one year prior to fMRI scanning (MPostSurgery1⁄43.9 years, SD1⁄41.6), and had an optimally adjusted band and stable weight loss (MEWL1⁄474.1%, SD1⁄416.4). A total of 7 patients were excluded. Patients completed 2 days of scanning after fasting at least 8 hours. One day was an actual deflation day during which approximately 50% of fluid was removed from the band port. A second day involved sham-deflation during which the patient’s port was accessed, fluid removed, and immediately replaced with no net change. Patients and assessors were blinded to condition, and deflation/sham-deflation days were counterbalanced. On both days, patients completed a form indicating their estimate (deflation/sham), followed by a milkshake paradigm in the scanner where they viewed cues of milkshake or tasteless solution and received the corresponding taste. BOLD activation to milkshake versus tasteless solution was analyzed using SPM8. Contiguous clusters with kZ25 were deemed significant at po.05 corrected, determined by 10,000 MonteCarlo simulations (Cox, 1996). Results: When deflated, patients showed significantly greater activation to milkshake cues versus tasteless solution cues in the cingulate gyrus (emotional control), inferior parietal lobule, and postcentral gyrus (somatosensory), and to the taste of milkshake versus tasteless solution in the thalamus (reward). In the sham-deflation condition, patients showed significantly greater activation to milkshake cues in the caudate (reward) and anterior cingulate cortex (emotion/reward), and to the taste of milkshake in the cingulate gyrus (emotional control), cuneus (visual processing), posterior insula (taste), and postcentral gyrus (somatosensory). Patients correctly identified the procedure as a deflation 66.7% of the time and as sham 75% of the time. Conclusions: Results indicate increased activation in somatosensory, emotional control, and reward regions to a high-calorie liquid when the band was deflated. In the sham-deflation condition, different regions involved in reward, taste, and emotion showed increased activation compared to the deflation condition. These regions have been found to be hyperactivated as well in obese adults and emotional eaters, suggesting that even LAGB patients in the “green zone” may still experience underlying neuronal patterns similar to obese adults. Although preliminary, these results suggest that deflation of the band affects neuronal responses involved in emotional control and reward processing. This is more evidence that LAGB is not solely a restrictive procedure, but also has a neuronal pathway which may be a factor contributing to successful weight loss maintenance. Further studies are needed to more clearly elucidate the precise neuronal mechanisms involved in successful weight loss.
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Apr 3, 2024
Hugo J R Bonatti + 2
Open Access