Sucrose’s sweet intensity is one attribute contributing to the overconsumption of high-energy palatable foods. However, it is not known how sucrose intensity is encoded and used to make perceptual decisions by neurons in taste-sensitive cortices. We trained rats in a sucrose intensity discrimination task and found that sucrose evoked a widespread response in neurons recorded in posterior-Insula (pIC), anterior-Insula (aIC), and Orbitofrontal cortex (OFC). Remarkably, only a few Intensity-selective neurons conveyed the most information about sucrose’s intensity, indicating that for sweetness the gustatory system uses a compact and distributed code. Sucrose intensity was encoded in both firing-rates and spike-timing. The pIC, aIC, and OFC neurons tracked movement direction, with OFC neurons yielding the most robust response. aIC and OFC neurons encoded the subject’s choices, whereas all three regions tracked reward omission. Overall, these multimodal areas provide a neural representation of perceived sucrose intensity, and of task-related information underlying perceptual decision-making.

No abstract

Sucrose's sweet intensity is one attribute contributing to the overconsumption of highenergy palatable foods. However, it is not known how sucrose intensity is encoded and used to make perceptual decisions by neurons in taste cortices. We trained rats in a sucrose intensity discrimination task and found that sucrose evoked a widespread response in neurons recorded in posterior (pIC), anterior (aIC) Insula, and Orbitofrontal cortex (OFC). Remarkably, only a few selective-neurons conveyed the most information about sucrose intensity, indicating that the taste system used a compact and distributed code for sweetness. Sucrose intensity was encoded in the firing rate and the spike timing. The pIC, aIC, and OFC neurons tracked movement direction, with OFC neurons providing the most robust response. aIC and OFC neurons encoded the subject's choices, whereas the three regions tracked reward omission. In sum, these three areas provide a neural representation of perceived sucrose intensity, and of task-related information underlying perceptual decision-making.

AcknowledgementsFigure illustrations were created using templates from BioRender.com. We extend our thanks to Dr. Florence Allain for assisting with the box illustrations for the figures and Jose-Maria Restrepo for assisting with the miniscope analysis. We also thank David Munro for assisting with the 3D print of the pellet dispenser component.

The intensity of sucrose (its perceived concentration) and its palatability (positive hedonic valence associated with ingestion) are two taste attributes that increase its attractiveness and overconsumption. Although both sensory attributes covary, in that increases in sucrose concentration leads to similar increases in its palatability, this covariation does not imply that they are part of the same process or whether they represent separate processes. Both these possibilities are considered in the literature. For this reason, we tested whether sucrose’s perceived intensity could be separated from its hedonically positive palatability. To address this issue, rats were trained in a sucrose intensity task to report the perceived intensity of a range of sucrose concentrations before and after its palatability was changed using a conditioned taste aversion (CTA) protocol. We found that the subjects’ performance remained essentially unchanged, although its palatability was changed from hedonically positive to negative. Overall, these data demonstrate that sucrose’s perceived intensity and its positive palatability can be dissociated, meaning that changes of one taste attribute render the other mostly unaffected. Thus, the intensity attribute is sufficient to inform the perceptual judgments of sucrose’s concentrations.