Offline stimulation of human parietal cortex differently affects resting EEG microstates

Abstract

The interference effects of transcranial magnetic stimulation (TMS) on several electroencephalographic (EEG) measures in both temporal and frequency domains have been reported. We tested the hypothesis whether the offline external inhibitory interference, although focal, could result in a global reorganization of the functional brain state, as assessed by EEG microstates. In 16 healthy subjects, we inhibited five parietal areas and used a pseudo stimulation (Sham) at rest. The EEG microstates were extracted before and after each stimulation. The canonical A, B, C and D templates were found before and after all stimulation conditions. The Sham, as well as the stimulation of a ventral site did not modify any resting EEG microstates' topography. On the contrary, interfering with parietal key-nodes of both dorsal attention (DAN) and default mode networks (DMN), we observed that the microstate C clearly changes, whereas the other three topographies are not affected. These results provide the first causal evidence of a microstates modification following magnetic interference. Since the microstate C has been associated to the activity in regions belonging to the cingulo-opercular network (CON), the regional specificity of such inhibition seems to support the theory of a link between CON and both DAN and DMN at rest.

Figure 1

Experimental design: (a) Temporal sequence for each rTMS stimulation condition. (b) View of the left and the right hemispheres atlas brain with regions obtained from a meta-analysis studies^,. Regions stimulated with rTMS in this experiment correspond to the following MNI coordinates (x, y, z in mm): right IPS: 23, −65, 48, right AG: 53, −67, 46, left IPS: −25, −63, 47, left AG: −47, −67, 36, and left TPJ: −52, −49, 17.

Figure 2

Topography of the four common resting EEG microstates in each rTMS condition (i.e. Sham, left TPJ, left AG, right AG, left IPS, right IPS) in the period that precedes (1 min, pre-TMS) and follows (1 min, post-TMS) the magnetic stimulation. Post-hoc test (performed by TANOVA): statistically significant differences between pre- and post-TMS periods in each condition are indicated by one asterisk (p < 0.005).