Optogenetic hedonic hotspots in orbitofrontal cortex and insula: causing enhancement of sweetness 'liking'.

Hedonic hotspots are brain subregions that causally amplify the hedonic impact of palatable tastes, measured as increases in affective orofacial 'liking' reactions to sweetness. Previously, two cortical hedonic hotspots in orbitofrontal cortex and insula were identified by neurochemical stimulation using opioid or orexin microinjections. Here we used optogenetic stimulation in rats as an independent neurobiological technique for activating cortical hedonic hotspots to identify hedonic functions and map boundaries. We report that channelrhodopsin stimulations within rostral orbitofrontal and caudal insula hotspots doubled the number of hedonic 'liking' reactions elicited by sucrose taste. This independently confirms their robust functional identity as causal amplifiers of hedonic 'liking' and confirms their anatomical boundaries. Additionally, we confirmed an intervening suppressive hedonic coldstrip, to stretching from caudal orbitofrontal cortex to rostral insula. By contrast to localized hedonic hotspots for 'liking' enhancement, motivational 'wanting' for reward, measured as laser self-stimulation, was mediated by more widely distributed anatomical sites.