The insula communicates tactile prediction error throughout a hierarchy of sensory and prefrontal areas

Embodied awareness is the pervasive, multimodal self-awareness that is thought to form the foundation of emotion. This awareness was recently proposed to rely on the anterior insular cortex (AIC) comparing expected and actual bodily signals arising in prefrontal and sensory cortices. To investigate this possibility in the somatosensory domain, we measured brain activity using functional magnetic resonance imaging while healthy human participants discriminated tactile stimuli varying in intensity and predictability. Dynamic Causal Modelling revealed that unexpected stimuli increased the strength of forward connections in a caudal to rostral ascending hierarchy from thalamic and somatosensory regions towards insula, cingulate and prefrontal cortices, consistent with hierarchical predictive coding. Within this feed-forward flow of neural coupling, the AIC increased both forwards and backwards connections to prefrontal and somatosensory cortex, supporting a comparator role. Further, we found that greater prefrontal to AIC connectivity predicted subjective ratings of stimulus discrimination difficulty. Importantly, AIC responses were insensitive to the intensity of deviants, in contrast to the posterior insula, second somatosensory and mid-cingulate cortex which responded preferentially to intense, unexpected stimuli. These results are interpreted in light of embodied predictive coding, suggesting that the AIC coordinates global cortical processing of tactile changes to support body awareness.