Reader response: Insular and anterior cingulate cortex deep stimulation for central neuropathic pain: Disassembling the percept of pain

Abstract

Galhardoni et al. evaluated the effect of repetitive transcranial magnetic stimulation (rTMS) on the anterior cingulate cortex (ACC) and posterior superior insula (PSI) of patients with central neuropathic pain (CNP). Multidimensional aspects of pain were evaluated with psychophysical tests, electrophysiologic recordings, and scales. rTMS in PSI increased the threshold for heat pain, whereas in ACC improved anxiety scores. It is plausible that the neuromodulation of these structures has a therapeutic potential for CNP. On the other hand, we recently pointed out that rTMS over PSI and ACC involve greater stimulation of superficial rather than deeper structures. In addition, estimation of the stimulation targets was based on a linear projection from the center of the coil. Linear projection does not correspond to the region of maximum induced electric field on internally folded cortical structures, which is always on the more superficial tissue; therefore, the clinical findings should not be regarded as the resultant of deep structures’ stimulation instead of an ensemble of stronger spread superficial stimulation combined with deeper stimulation. Accordingly, electric field modeling may be used to guide the coil positioning and adjustment of stimulation intensity to achieve a significant pain relief. Certainly, there is great importance in the development of new therapeutic strategies for CNP.