Emotional processing impairments in patients with insula lesions following stroke.

Functional imaging has helped to understand the role of the human insula as a major processing network for integrating input with the current state of the body. However, these studies remain at a correlative level. Studies that have examined insula damage show lesion-specific performance deficits. Case reports have provided anecdotal evidence for deficits following insula damage, but group lesion studies offer a number of advances in providing evidence for functional representation of the insula. We conducted a systematic literature search to review group studies of patients with insula damage after stroke and identified 23 studies that tested emotional processing performance in these patients. Eight of these studies assessed emotional processing of visual (most commonly IAPS), auditory (e.g., prosody), somatosensory (emotional touch) and autonomic function (heart rate variability). Fifteen other studies looked at social processing, including emotional face recognition, gaming tasks and tests of empathy. Overall, there was a bias towards testing only patients with right-hemispheric lesions, making it difficult to consider hemisphere specificity. Although many studies included an overlay of lesion maps to characterise their patients, most did not differentiate lesion statistics between insula subunits and/or applied voxel-based associations between lesion location and impairment. This is probably due to small group sizes, which limit statistical comparisons. We conclude that multicentre analyses of lesion studies with comparable patients and performance tests are needed to definitively test the specific function of parts of the insula in emotional processing and social interaction.

The Role of Left Hemispheric Structures for Emotional Processing as a Monitor of Bodily Reaction and Felt Chill - a Case-Control Functional Imaging Study.

Background: The particular function of the left anterior human insula on emotional arousal has been illustrated with several case studies. Only after left hemispheric insula lesions, patients lose their pleasure in habits such as listening to joyful music. In functional magnetic resonance imaging studies (fMRI) activation in the left anterior insula has been associated with both processing of emotional valence and arousal. Tight interactions with different areas of the prefrontal cortex are involved in bodily response monitoring and cognitive appraisal of a given stimulus. Therefore, a large left hemispheric lesion including the left insula should impair the bodily response of chill experience (objective chill response) but leave the cognitive aspects of chill processing (subjective chill response) unaffected. Methods: We investigated a patient (MC) with a complete left hemispheric media cerebral artery stroke, testing fMRI representation of pleasant (music) and unpleasant (harsh sounds) chill response. Results: Although chill response to both pleasant and unpleasant rated sounds was confirmed verbally at passages also rated as chilling by healthy participants, skin conductance response was almost absent in MC. For a healthy control (HC) objective and subjective chill response was positively associated. Bilateral prefrontal fMRI-response to chill stimuli was sustained in MC whereas insula activation restricted to the right hemisphere. Diffusion imaging together with lesion maps revealed that left lateral tracts were completely damaged but medial prefrontal structures were intact. Conclusion: With this case study we demonstrate how bodily response and cognitive appraisal are differentially participating in the internal monitor of chill response.