Functional Connectivity of the Motor System defined by Transcranial Electric Stimulation (TES)

In the visual system we have previously shown that concurrent transcranial electrical stimulation (TES) and functional Magnetic Resonance Imaging (fMRI) can identify distant effects due to focal stimulation. The goal of this project is to re-investigate the disseminated human motor cortical network with simultaneous TES, fMRI and Electromyography (EMG). FMRI is the method of choice for non-invasive research of the human brain at high spatial resolution. Combined with TES one can modulate brain function within milliseconds with high temporal resolution. State of the Art research allows for inhibitory and excitatory stimulation protocols with long lasting as well as briefly transient effects. The effect of stimulation can be controlled peripherally with simultaneous EMG acquisition. We stimulated the human brain over the primary motor cortex with TES every 18s, with a 1mV EMG response, in an event-related fMRI study. 16 slice 3T fMRI data was acquired every 3 seconds to allow for 20 trials. Further data was acquired for a nociceptive control. Functional and structural fMRI data were pre-processed and analyzed following standard procedures for 3Tesla fMRI-Data and event-related GLM-Analysis within the MATLAB ® Toolbox SPM2 (Statistical Parametric Mapping, UCL, London). Bilateral electrophysiological data was scrutinized for spurious subject movement, amplitude (1 mV) and delay (19 +/- 3ms) and also defined the onset times of muscle response in the event-related data analysis. By combining TES and fMRI co-activations were identified in all nodes of a network strictly confined to predefined regions of interest in line with a synopsis of previous motor system research. These regions included bilateral primary and secondary motor areas, primary and secondary sensory areas, the mesial wall with cingulate-, precingulate, supplementary- and presupplementary motor areas as well as the thalamus, the insula and the lateral occipital cortex. In contradistinction to repetitive TMS-stimulation, event-related TES-stimulation elicited a positive hemodynamic response in the contralateral motor areas. We conclude that TES and fMRI are feasibly utilized to research functional networks of the human brain and that these connections are not task related or likely of spurious nature (i.e. movement of the non-dominant hand).