Modality-specific and modality-general representations of reward value in frontal cortex

Standard neuroeconomics theories state that the value of different classes of stimuli, for instance the hedonic value of food versus music, is transformed to a common reference scale that is independent of their sensory properties. However, adaptive behaviour in a multimodal and dynamic environment requires that our brain also encodes information about the sensory features of reward predicting stimuli. Whether and how a common code for value could integrate information about the sensory features of rewarding stimuli remains inadequately understood. By employing stimuli from auditory and visual modalities as reward predicting cues in a value-based decision-making task, we were able to vary the reward value and sensory modality independently and dissociate neural codes of auditory and visual rewards in frontal areas using fMRI. Univariate fMRI analysis revealed modality-specific and modality-general value representations in orbitofrontal cortex (OFC) and ventromedial prefrontal cortex (vmPFC), respectively. Crucially, modality-specific representations were highly selective as they were only activated when participants believed that the corresponding sensory modality was associated with reward and were absent when the task involved instruction-based rather than value-based choices. Moreover, we show that modality-specific value representations are supported by the presence of the effective connectivity between each primary sensory area and the corresponding OFC activation and further between modality-specific value representations in OFC and vmPFC, only when the sensory modality to be chosen is associated with reward and absent otherwise. Our results indicate the presence of both modality-specific and modality-general representations of reward value and reveal mechanisms through which the interaction between the sensory cortices and the two types of representation guides value-based decisions.