Low- and High-Frequency Repetitive Transcranial Magnetic Stimulation Effects on Resting-State Functional Connectivity Between the Postcentral Gyrus and the Insula

Abstract

The insular cortex supports the conscious awareness of physical and emotional sensations, and the ability to modulate the insula could have important clinical applications in psychiatry. Repetitive transcranial magnetic stimulation (rTMS) uses transient magnetic fields to induce electrical currents in the superficial cortex. Given its deep location in the brain, the insula may not be directly stimulated by rTMS; however, rTMS may modulate the insula via its functional connections with superficial cortical regions. Furthermore, low-versus high-frequency rTMS is thought to have opposing effects on cortical excitability, and the present study investigated these effects on brain activity and functional connectivity with the insula. Separate groups of healthy participants (n = 14 per group) received low (1 Hz)-or high (10 Hz)-frequency rTMS in five daily sessions to the right postcentral gyrus, a superficial region known to be functionally connected to the insula. Resting-state functional connectivity (RSFC) was measured pre-and post-rTMS. Both 1 and 10 Hz rTMS increased RSFC between the right postcentral gyrus and the left insula. These results suggest that low-and high-frequency rTMS has similar long-term effects on brain activity and RSFC. However, given the lack of difference, we cannot exclude the possibility that these effects are simply due to a nonspecific effect. Given this limitation, these unexpected results underscore the need for acoustic-and stimulation-matched sham control conditions in rTMS research.

Effects of repetitive transcranial magnetic stimulation on resting-state connectivity: A systematic review

“…For example, by stimulating parietal regions with strong baseline resting-state functional connectivity (RSFC) to a hippocampal target, Wang et al (2014) showed that rTMS was able to modify the connectivity between these structures. Similar promising results were found when rTMS was applied over the premotor cortex to modulate the insula ( Addicott et al, 2019 ). Interestingly, this study found that both 1 Hz and 10 Hz rTMS induced increased functional connectivity, despite the fact that these two frequencies of rTMS have previously been associated with opposing effects on the activity of the proximal stimulated region (inhibitory for 1 Hz versus excitatory for 10 Hz).…”

Repetitive transcranial magnetic stimulation modulates cortical–subcortical connectivity in sensorimotor network

“…Thus, we speculated that the increased activities in cortical regions and decreased activities in subcortical regions may induce the reduction of connectivity between cortical and subcortical areas within the cortico‐basal ganglia thalamo‐cortical circuits after 3‐Hz HF stimulation. On the other hand, the connectivity alteration after LF rTMS in the current study was in line with previous studies, which found that the LF rTMS holds the ability to increase the connectivity between cortical and the subcortical regions (Addicott et al, 2019; Eldaief et al, 2011; Flamez et al, 2021). For example, Flamez et al (2021) found that, after 1‐Hz rTMS intervention, the FC between stimulated right pre‐supplementary motor area and ipsilateral PUT was significantly increased in patients with Parkinson's disease.…”

Abnormal Ventral Somatomotor Network Homogeneity in Patients With Temporal Lobe Epilepsy

“…As reported by DiGuiseppi et al (35), axons from the ventral posterolateral nucleus travel from the thalamus through the posterior limb of the internal capsule and terminate in the appropriate region of the postcentral gyrus. The postcentral gyrus has numerous connections with other brain areas, including the insula (36), amygdala (37), limbic system (38), cerebellum (39), and parietal lobe (40). Because of these numerous connections, the postcentral gyrus is able to perform a variety of functions, including those involved in somatic perceptual processes.…”