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Summary: Perception of the smell of a food precedes its ingestion and perception of its flavor. The neurobiological underpinnings of this association are not well understood. Of central interest is whether the same neural circuits code for anticipatory and consummatory phases. Here, we show that the amygdala and mediodorsal thalamus respond preferentially to food odors that predict immediate arrival of their associated drink (FO+) compared to food odors that predict delivery of a tasteless solution (FO−) and compared to the receipt of the drink. In contrast, the left insula/operculum responds preferentially to the drink, whereas the right insula/operculum and left orbitofrontal cortex respond to FO+ and drink. These findings indicate separable and overlapping representation of anticipatory and consummatory chemosensation. Moreover, since ratings of perceived pleasantness of FO+, FO−, and drink were similar, the response in the amygdala and thalamus cannot reflect acquired affective value but rather predictive meaning or biological relevance. [Copyright &y& Elsevier]

Summary Post-ingestive signals related to nutrient metabolism are thought to be the primary drivers of reinforcement potency of energy sources. Here, in a series of neuroimaging and indirect calorimetry human studies, we examine the relative roles of caloric load and perceived sweetness in driving metabolic, perceptual, and brain responses to sugared beverages. Whereas caloric load was manipulated using the tasteless carbohydrate maltodextrin, sweetness levels were manipulated using the non-nutritive sweetener sucralose. By formulating beverages that contain different amounts of maltodextrin+sucralose, we demonstrate a non-linear association between caloric load, metabolic response, and reinforcement potency, which is driven in part by the extent to which sweetness is proportional to caloric load. In particular, we show that (1) lower-calorie beverages can produce greater metabolic response and condition greater brain response and liking than higher-calorie beverages and (2) when sweetness is proportional to caloric load, greater metabolic responses are observed. These results demonstrate a non-linear association between caloric load and reward and describe an unanticipated role for sweet taste in regulating carbohydrate metabolism, revealing a novel mechanism by which sugar-sweetened beverages influence physiological responses to carbohydrate ingestion. [ABSTRACT FROM AUTHOR]

Summary: A new electrophysiological study in rodents demonstrates that taste–odor convergence occurs in posterior piriform olfactory cortex and calls for a reformulation of classic models of the central representation of flavor. [ABSTRACT FROM AUTHOR]

Summary: Identification of energy sources depends upon the ability to form associations between food cues and nutritional value. As such, cues previously paired with calories elicit neuronal activation in the nucleus accumbens (NAcc), which reflects the reinforcing value of food [1–4]. The identity of the physiological signals regulating this response remains elusive. Using fMRI, we examined brain response to noncaloric versions of flavors that had been consumed in previous days with either 0 or 112.5 calories from undetected maltodextrin. We report a small but perceptually meaningful increase in liking for the flavor that had been paired with calories and find that change in liking was associated with changes in insular responses to this beverage. In contrast, NAcc and hypothalamic response to the calorie-paired flavor was unrelated to liking but was strongly associated with the changes in plasma glucose levels produced by ingestion of the beverage when consumed previously with calories. Importantly, because each participant ingested the same caloric dose, the change in plasma glucose depended upon individual differences in glucose metabolism. We conclude that glucose metabolism is a critical signal regulating NAcc and hypothalamic response to food cues, and that this process operates independently from the ability of calories to condition liking. [ABSTRACT FROM AUTHOR]

There is a general consensus that overconsumption of sugar-sweetened beverages contributes to the prevalence of obesity and related comorbidities such as type 2 diabetes (T2D). Whether a similar relationship exists for no- or low-calorie "diet" drinks is a subject of intensive debate and controversy. Here, we demonstrate that consuming seven sucralose-sweetened beverages with, but not without, a carbohydrate over 10 days decreases insulin sensitivity in healthy human participants, an effect that correlates with reductions in midbrain, insular, and cingulate responses to sweet, but not sour, salty, or savory, taste as assessed with fMRI. Taste perception was unaltered and consuming the carbohydrate alone had no effect. These findings indicate that consumption of sucralose in the presence of a carbohydrate rapidly impairs glucose metabolism and results in longer-term decreases in brain, but not perceptual sensitivity to sweet taste, suggesting dysregulation of gut-brain control of glucose metabolism., Competing Interests: Declaration of Interests Authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)