Role of the rostral agranular insular cortex in the modulation of neuropathic pain produced by stimulation of the motor cortex

Abstract

Motor cortex stimulation (MCS) has been used to control various pain disorders in clinical field. Though functional imaging studies revealed that there were many other structures involved, the mechanisms of pain control by MCS are still poorly understood. To investigate the role of insular cortex on neuropathic pain modulation of MCS, we made unilateral lesion in rostral agranular insular cortex (RAIC) and compared with non-lesion model during MCS. We made 2 groups; Group A (n = 7); neuropathic pain (spared nerve injury model) + MCS, and Group B (n = 8); neuropathic pain + RAIC lesion + MCS. We measured the threshold and latency of pain in pre-stimulation and intra-stimulation phase using behavioral test. Pain threshold was increased in group A with “MCS on” and group B either “MCS off” or “MCS on”. Particularly, the threshold of group B with “MCS on” was higher than that of group B with “MCS off” or group A. The latency of bearing painful stimulus was also increased in group A with “MCS on” and group B either “MCS off” or “MCS on”. Also the latency was increased in group B with “MCS on” more than that of group B with “MCS off” or group A. Therefore, MCS and insular lesioning are possible participants in pain modulation. Compared with “MCS off”, significant changes after “MCS on” were noted on electrophysiologic study using the percentage change in spontaneous activity from RAIC. So our results showed that the RAIC has its own pain modulation effect and its effect is influenced by MCS