P 142. Functional connectivity of the left somatosensory cortex and the putative mirror neuron system

Abstract

Several brain areas have been identified as active during action perception and execution (see Rizzolatti and Sinigaglia, 2010). This parieto-frontal system of regions has been referred to as the putative Mirror Neuron System (pMNS). Primary somatosensory cortex (SI), has also been shown to be active during action perception and execution (see Keysers et al., 2010) but whether it is part of the pMNS or a separate somatosensory network, is still not clear. To answer this question we chose to deliver inhibitory Transcranial Magnetic Stimulation (TMS) (the protocol used was continuous theta burst (cTBS, see Huang et al., 2005) over the left SI and then collect resting state functional magnetic resonance (RSfMRI) data from our subjects. 18 healthy volunteers participated in a three days study. On Day 1, subjects were scanned while observing and performing simple single-handed actions. The target area for the stimulation was selected as the part of SI active in both conditions (see Fig. 1A). On the other two days in a randomized order subjects received cTBS or sham stimulation over the left SI. After stimulation participants were transported to the scanner and RSfMRI data was collected. Three different types of functional connectivity analysis were applied to the data from Day 2 and Day 3: (1) a seed-based correlational approach, (2) partial correlations between the nodes of the pMNS and (3) independent component analysis (ICA). The seed based correlational approach indicated a small decrease in the connectivity between the left SI and the dorsal premotor areas (dPM) after cTBS as compared to sham (cluster level corrected p (FWE) = 0.09; T = 4.47). Partial correlation analysis between the nodes of the pMNS calculated separately for the data from the sham and cTBS sessions suggested a decrease in the connectivity between the stimulated region and the left dorsal premotor area (dPM), part of the pMNS. ICA, which enables differentiation of independent functional networks, suggested a decrease in the synchronization of one network as a result of cTBS stimulation to SI (cluster level corrected p (FWE) = 0.03; T = 6.59) after cTBS. The change was localized in the same area of the left dPM as identified in the other two analyses (see Fig. 1B). Taken together our results suggest that the effect of inhibitory stimulation over the left SI is not focal but visible in the functionally connected distal brain areas. ICA analysis indicates that SI is part of the same functional network which includes the regions of the pMNS, but the seed based and partial correlation analyses show that this connection is disrupted by our stimulation, i.e. stimulation over SI does not have an effect on the synchronization of the network as a whole but causes a decrease of the connectivity between SI and dPM. Considering their co-activation during mental simulations of actions, we propose that SI also belongs to the pMNS.