Figure 1.
Cortico-cortical interactions explored with combined multifocal TMS and resting-state fMRI.
A) Left posterior parietal cortex (PPC) TMS preceded left M1 TMS by 5 ms and induced increased MEP amplitude, indicating intra-hemispheric functional connectivity (blue arrow and blue column). When a third conditioning pulse was applied 10 ms earlier to contralateral PPC, the left intrahemispheric interaction was abolished, reflecting the activation of a transcallosal inhibitory pathway (red arrow and red column). B) Mean normalized MNI coordinates (x, y, z, mean±SD) of TMS PPC site were −48.2±4.8, –65.2±3.9, and 45.3±3.4 mm in the left hemisphere and 52.5±6.3, −60.2±4.7 in the right hemisphere. Mean MNI coordinates of left M1 were −30±3.3, −12±3.4, and 71±4.3.
Figure 2.
Three-dimensonal rendering of the resting state networks estimated by independent components analysis.
The default mode network (DMN) has been linked to self-oriented mental activity; the dorsal-attention network (DAN) has been associated with goal-directed stimulus-response selection; The visual network (VisNet) has been associated with visual processing; the auditory network (AudNet) has been associated to processing of auditory stimuli; the left-lateralized fronto-parietal network (LFPN) and the right-lateralized fronto-parietal network (RFPN) have been associated to memory functions; the sensory-motor network (SMN) comprises primary sensory-motor areas and the supplementary motor area. For the correlation analysis, we selected the DMN, the DAN, and the SMN, based on anatomical considerations. See text for further details.
Figure 3.
correlation between TMS and fMRI data.
In panel A and B, areas of correlation between the dorsal attention network (DAN) and bifocal TMS are shown in green, while correlations between the DAN and trifocal TMS are shown in red. Overlapping regions are in yellow. Panel B also shows the sites of TMS stimulation (blue dots). The scatterplots reported in the upper row of panel C show the mean cluster Z-score (indicating the strength of functional connectivity estimated by resting state fMRI) against the percentage change in MEP for the 3 highlighted regions. In the lower raw of panel C, the corresponding mean Z-score relative to the default mode network (DMN) are also plotted against the percentage change in MEP (bottom row), but correlations were not significant. The directions of correlation (direct or inverse) are reversed in the two cases (bifocal and trifocal TMS) as expected due to the opposite (excitatory or inhibitory) nature of the underling connections. R and p values are estimated post-hoc using Pearson's correlation coefficient. See text for further details.
Table 1.
Results of the voxel-wise correlation between TMS and fMRI data.
Table 2.
Results of post-hoc correlation performed between TMS measures of connectivity and fMRI time-courses.