Subregional heterogeneity of somatosensory dysfunction in the insula

Somatosensory functions are subdivided into two large groups: the elementary somatosensory functions, which consist of light touch, pain, thermal sensation, joint position sense and vibration sense, and the intermediate somatosensory functions, which include two-point discrimination, tactile localisation, weight, texture and shape perception. It is generally accepted that the functional localisation of somatosensory function is the postcentral gyrus, but some researchers suggested that the insula is also involved in somatosensory function.1 Insula is a multimodal area and has a major role as a convergence zone implicated in the coordination between internal and external information through emotional subjective awareness. However, the subregional specificity of somatosensory functions in the insula has not been fully elucidated.2 We experienced three cases of stroke restricted exactly to the subregions of the insula which showed heterogeneous somatosensory dysfunction. For these patients, we performed a close examination of the intermediate somatosensory function, and discussed the relation between the insula and intermediate somatosensory function. ### Patient 1 An 81-year-old, right-handed woman who had difficulty speaking in February 2017 was transferred to our hospital. MRI revealed a lesion in the right middle insula (figure 1A). The symptom improved at the time of hospital arrival and she underwent the best medical treatment. The symptom disappeared on the next day. Intelligence and elementary somatosensory functions were normal. The results of the intermediate somatosensory examinations showed that two-point discrimination, tactile localisation and graphesthesia were significantly impaired. Figure 1 MRI findings of the cases presented. (A) Patient 1 had a cortical lesion in the right middle insula. (B) Patient 2 had a cortical lesion in the …