Interfering with the activity of the insular cortex to modulate interoceptive awareness: a combined TMS/fMRI study

Aims: Insular cortex (IC) is involved in sensing, interpreting and being aware of signals coming from the viscera, an ability called interoceptive awareness (IA), the lack of which is considered a transdiagnostic risk factor for psychopathology1. However, it is still unknown if and to what extent it is possible to modulate IC activity to eventually modify individuals’ IA by using noninvasive brain stimulation techniques. Transcranial magnetic stimulation, including theta-burst stimulation (TBS) protocols, has proven to be an effective method to non-invasively modulate a variety of cortical regions' activity, producing facilitatory (iTBS) or inhibitory (cTBS) effects. It has been recently demonstrated that cTBS delivered over a fronto-temporal region changes participants’ performance at the heartbeat counting task2, a measure of IA. However, it has not been tested yet if this is because TBS changes excitability of the IC. By combining TBS with fMRI, we hypothesized that iTBS and cTBS would affect IC activity and, consequently, interoceptive awareness. Materials and Methods: 22 healthy individuals (13 F/ 9 M; mean age: 23.86 ± 3.91 years) participated in this study. cTBS and iTBS, over the right anterior IC and a sham stimulation over a control brain region were administered in a counterbalanced order across participants. After each stimulation, participants performed an IA task and were scanned throughout a MRI 3T Siemens, while performing an explicit emotional judgment task. During this task, they saw disgusting or neutral images from the dataset DIRTI3 that has proven to consistently activate the insula. The task was composed by 20 blocks, and each block was composed by six images. After each block of images, participants reported on a 5-point Likert scale how much they felt disgusted. Results: We found preliminary evidence indicating that the two TBS sessions changed bilateral IC activation. In particular, the cTBS, reduced bilateral activation of the anterior IC when disgusting images were displayed. Discussion and Conclusions: Given the growing use of TMS protocols in psychiatry, current results could be used to inform the conduction of clinical trials aimed at facilitating or inhibiting the activity of the insular cortex (for example in patients showing impaired interoception) with the ultimate goal to harness scientific advances to select treatment options with the greatest likelihood of success. 1)Craig, A. D. (2009). How do you feel—now? The anterior insula and human awareness. Nature reviews neuroscience, 10(1), 59-70. 2)Pollatos, O., Herbert, B. M., Mai, S., & Kammer, T. (2016). Changes in interoceptive processes following brain stimulation. Philosophical Transactions of the Royal Society B: Biological Sciences, 371(1708) 3)Haberkamp, A., Glombiewski, J. A., Schmidt, F., & Barke, A. (2017). The DIsgust-RelaTed-Images (DIRTI) database: Validation of a novel standardized set of disgust pictures. Behaviour research and therapy, 89, 86-94.