Reinforcement learning from post-ingestive calories: from body to brain in health and disease

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Publication . Ribeiro, Gabriela; Camacho, Marta; Fernandes, Ana B; Cotovio, Gonçalo; Torres, Sandra; Oliveira-Maia, Albino J

Background Reward sensitivity has been proposed as a potential mediator of outcomes for bariatric surgery. Objectives We aimed to determine whether gustatory and psychometric measures of reward-related feeding are predictors of bariatric-induced weight loss. Methods A multicenter longitudinal cohort study was conducted in patients scheduled for bariatric surgery (surgical group), assessed at baseline and 2 follow-up assessments. Predictions of % weight loss from baseline (%WL) according to baseline gustatory measures, including intensity and pleasantness ratings of sweet and other tastants, and psychometric measures of reward-related feeding behavior, including hedonic hunger scores, were assessed with multivariable linear regression. Exploratory analyses were conducted to test for associations between %WL and changes in gustatory and psychophysical measures, as well as for comparisons with data from patients on the surgery waiting list (control group). Results We included 212 patients, of whom 96 in the surgical group and 50 in the control group were prospectively assessed. The groups were similar at baseline and, as expected, bariatric surgery resulted in higher %WL (BTreatment-Time = 2.4; 95% CI: 2.1–2.8; P < 0.0001). While variation in gustatory measures did not differ between groups, in the surgery group baseline sweet intensity predicted %WL at the primary endpoint (11 to 18 months postoperatively; β = 0.2; B = 0.2, 95% CI: 0.02 to 0.3; P = 0.02), as did hedonic hunger scores (β = −0.2; B = −2.0, 95% CI: −3.8 to −0.3; P = 0.02). Furthermore, at this endpoint, postsurgical reduction of sweet taste intensity and acceptance of sweet foods were associated with %WL (β = −0.3; B = −3.5, 95% CI: −5.8 to −1.3; P = 0.003, and β = −0.2; B = −4.7, 95% CI: −8.5 to −0.8; P = 0.02, respectively). The use of sweet intensity as a predictor of weight change was confirmed in another bariatric cohort. Conclusions Sweet intensity ratings and hedonic hunger scores predict %WL after surgery. The variability of sweet intensity ratings is also associated with %WL, further suggesting they may reflect physiological processes that are variably modulated by bariatric surgery, influencing clinical outcomes.

2021Journal article

Open access

Sweet taste and obesity

Publication . Ribeiro, Gabriela; Oliveira-Maia, Albino J.

For more than 50 years, there has been evidence for greater consumption of sweet- foods in overweight humans and animals, relative to those that have a normal weight. Furthermore, it has long been suggested that energy deficit resulting from dieting, while moving the individual from a higher weight set point, would result in heightened susceptibility to palatable tastants, namely to sweet tastants. This was the motivation behind the first studies comparing sweet taste perception between individuals with obesity and those of a normal weight. These studies, using direct measures of taste, have been characterized by significant methodological heterogeneity, contributing towards variability in results and conclusions. Nevertheless, some of these findings have been used to support the theory that patients with obesity have decreased taste perception, particularly for sweet tastants. A similar hypothesis has been proposed regarding evidence for reduced brain dopamine receptors in obesity and, in both cases, it is proposed that increased food consumption, and associated weight gain, result from the need to increase sensory and brain stimulation. However, the available literature is not conclusive on the association between obesity and reduced sweet taste perception, with both negative and contradictory findings in comparisons between individuals with obesity and normal weight control subjects, as well as within-subject comparisons before and after bariatric surgery. Nevertheless, following either Roux-en-Y gastric bypass or sleeve gastrectomy, there is evidence of changes in taste perception, particularly for reward-related measures of sweet tastants, that should be further tested and confirmed in large samples, using consensual methodology.

2021-10Journal article

Open access

Explicit knowledge of task structure is a primary determinant of human model-based action

Publication . Castro-Rodrigues, Pedro; Akam, Thomas; Snorasson, Ivar; Camacho, Marta; Paixão, Vitor; Maia, Ana; Barahona-Corrêa, J. Bernardo; Dayan, Peter; Simpson, H. Blair; Costa, Rui M.; Oliveira-Maia, Albino J.

Explicit information obtained through instruction profoundly shapes human choice behaviour. However, this has been studied in computationally simple tasks, and it is unknown how model-based and model-free systems, respectively generating goal-directed and habitual actions, are affected by the absence or presence of instructions. We assessed behaviour in a variant of a computationally more complex decision-making task, before and after providing information about task structure, both in healthy volunteers and in individuals suffering from obsessive-compulsive or other disorders. Initial behaviour was model-free, with rewards directly reinforcing preceding actions. Model-based control, employing predictions of states resulting from each action, emerged with experience in a minority of participants, and less in those with obsessive-compulsive disorder. Providing task structure information strongly increased model-based control, similarly across all groups. Thus, in humans, explicit task structural knowledge is a primary determinant of model-based reinforcement learning and is most readily acquired from instruction rather than experience.

2022-05Journal article

Open access