The role of insular cortex in reward learning

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Sensory information can be used as clue for identifying objects, both rewarding objects and aversive objects. However, learning process would be required to use that information as clue. The association between sensory information and rewarding outcome would modify neural circuits and probably contribute to change value of the sensory cue. Although many brain areas are involving eating behavior, it is poorly known which neurons in the circuit mediate the ability to identify edible foods. One important region that may supply valence information is the insular cortex. The insular cortex is a brain region that integrates incoming sensory information including somatosensory and visceral information and is also known as the taste cortex. Furthermore, recent findings suggest that through the integration of information coming from visceral cues and sensory component of rewarding objects, insular cortex neurons can powerfully modulate appetitive behaviors. Therefore, I hypothesize that neural circuit that involve in cue-reward learning will also be made and refined in the insular cortex during cue-reward association learning training. Major purpose of this research is to confirm whether synaptic inputs into insular cortex neurons would be potentiated during cue-reward association learning training. To get more precise anatomical information about neuronal connection in the insular cortex, observation of afferent inputs into insular cortex by labeling neurons retrogradely using tracer called Fluorogold was performed. Pavlovian conditioning task was used as a model behavior of cue-reward learning. Mice learned association between sensory cue and food reward within one week. To confirm insular cortex is involved to this behavior, pharmacological experiments were performed. Electrophysiological approach was used to measure synaptic inputs into insular cortex neurons.