Optogenetic Hedonic Hotspots in the Orbitofrontal Cortex and Insula: Causing Enhancement of Sweetness "Liking"

Hedonic hotspots are localized brain sites where appropriate stimulations can amplify the hedonic impact of palatable tastes, measured as increases in affective orofacial "liking" reactions to sweetness in rodents. Previously, two cortical hedonic hotspots in the orbitofrontal cortex and insula were identified using opioid or orexin microinjections as neurochemical manipulations. Here we used optogenetic stimulation in male and female rats to independently confirm the sites and boundaries of two cortical hedonic hotspots, as well as their special hedonic enhancement functions. We report that channelrhodopsin stimulations within the two hedonic hotspots of rostral orbitofrontal and caudal insula each doubled the number of hedonic "liking" reactions elicited by sucrose taste. Additionally, we confirmed that an intervening suppressive hedonic coldstrip stretches between them, where stimulation reduced "liking" reactions. In contrast to the localization of hedonic hotspots for "liking" enhancement, motivational "wanting" for reward, measured as laser self-stimulation, was mediated by more widely distributed cortical sites in both hotspots and coldstrip.