O152 Investigating effective connectivity in the motor network with TMS-evoked cortical potentials

Objectives Our purpose was to learn what the spatial distribution of transcranial magnetic stimulation (TMS)-evoked potentials can reveal about connectivity originating from premotor, supplementary, and primary motor cortices. Methods The data were collected with the combination of navigated TMS (nTMS) and EEG from four subjects (one subject reported here). The primary, pre-, and supplementary motor cortices in both hemispheres were stimulated, each area receiving 150 pulses at stimulation intensity of 90% of the electric field of ipsilateral APB motor threshold. The EEG datasets were preprocessed with novel artifact-removal algorithms (Mutanen et al., NeuroImage 2016). The first four peaks and their latencies were determined from the global mean field amplitudes (GMFA). At these peak latencies, minimum-norm estimates (MNE) indicated sites of most prevalent cortical activity. Results The new artifact-removal method proved to be useful as the first step in the data analysis. The spreading of neuronal activity depends on the stimulation target; the order of the activated cortical areas varies when different motor-related areas are stimulated. Discussion Our combination of experimental settings, data processing tools, and data-analysis methods can be used to evaluate effective connections from motor areas. Cortical activation patterns differ depending on the stimulated motor area. Conclusions nTMS–EEG can be used to investigate the connectivity originating from motor areas. Significance nTMS–EEG may be used to select stimulation sites on the cortex when specific neuronal connections should be strengthened by TMS, for example, in stroke patients.