Consistent with Sherrington’s classic distinction between exteroception and interoception ( Sherrington, 1906) – sensation of an object in the external environment vs. If these hedonic afferents reflect the internal physiological condition of the body more than external sensory events, then this would provide evidence for a unique dual role of our proximal senses. It has been proposed that such valence discrimination in peripheral receptors contributes to internal representations of homeostatic threat and social safety ( Craig, 2011, 2015). However, there is evidence that hedonic valence (good vs bad) is coded by the peripheral afferents of the somatosensory system ( Iggo, 1959, 1960 Vallbo et al., 1999) suggesting that aspects of tactile sensation are valenced from the point of contact ( Miskovic and Anderson, 2018). In contrast, hedonic appraisal is regarded as a subjective centrally mediated process ( Rolls, 2019 Todd et al., 2020), dependent on allocation of a mental common currency ( McFarland and Sibly, 1975 Rolls, 2000) to estimate and compare affective value. The information processed by our sensory systems is typically viewed as objective, forming representations of a tangible external environment. Sensory experiences, such as embrace of a loved one or the pain of a stubbed toe, can be broken down into two central components: discrimination of the sensory information, and the associated hedonic response. This suggests that touch should be divided into external-exteroceptive and internal-interoceptive dimensions, with hedonic touch represented as an internal state, even though evoked by external stimulation. By contrast, all hedonic touch representations were identified in regions associated with affect and interoception. Employing representational similarity analysis with a new approach of pattern component modeling, we decomposed multivoxel patterns to demonstrate that signals of painful but not pleasurable touch are represented in primary somatosensory cortices. Yet it remains unknown whether the central nervous system represents tactile hedonic information in sensory cortices as another dimension of exteroceptive information, similar to discriminative touch signals, or if tactile hedonic information is instantiated in regions mediating internal interoceptive states. Pleasure and pain signals travel along peripheral nerve pathways distinct from those for discriminative touch. In the somatosensory system, hedonic information is coded by mechanoreceptors at the point of contact.
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