Anatomical and functional enhancements of the insula after loss of large primary somatosensory fibers

Brain changes associated with the loss of a sensory modality such as vision and audition have previously been reported. Here, we examined the effect of loss of discriminative touch and proprioception on cortical thickness and functional connectivity. We performed structural magnetic resonance imaging and resting-state functional magnetic resonance imaging scans on a 60-year-old female who at age 31 suffered a selective loss of large-diameter myelinated primary afferents and, therefore, relies mainly on her intact thin-fiber senses (temperature, pain, itch, and C-fiber touch) and vision to negotiate her environment. The patient showed widespread cortical thinning compared with 12 age-matched female controls. In contrast, her right anterior insula was significantly thick. Seed-based resting-state analysis revealed that her right anterior insula had increased connectivity to bilateral posterior insula. A separate independent component analysis revealed the increased connectivity between the insula and visual cortex in the patient. As the insula is an important processing area for temperature and C-fiber tactile information, the increased intrainsular and insular-visual functional connectivity could be related to the patient's use of C-fiber (gentle) touch and temperature information in conjunction with visual information to navigate her environment. We, thus, demonstrated plasticity in networks involving the insular cortex following denervation of large-diameter somatosensory afferents.