Poster B12, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
A model to investigate effective connectivity in the speech network with TMS-evoked cortical potentials
Pantelis Lioumis1,2, Karita Salo1,2, Selja Vaalto1,3, Risto Ilmoniemi1,2;1Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, 2BioMag Laboratory, HUS Medical Imaging Center, Helsinki University Hospital, 3Department of Clinical Neurophysiology, HUS Medical Imaging, Helsinki University Hospital
Introduction: To observe how the spatial distribution of transcranial magnetic stimulation (TMS)-evoked potentials can be utilized to study connectivity originating from the right-hemispheric homologue to Broca’s area. Methods: The data were collected by combining navigated TMS (nTMS) and electroencephalography (EEG) in three subjects. The right-hemispheric homologue of Broca’s area (opIFG) was stimulated by targeting 150 pulses at a stimulation intensity inducing the corresponding electric field as 90% of the motor threshold of the left APB in M1. The EEG datasets were preprocessed with novel artifact-removal algorithms (Mutanen et al., NeuroImage 2016). The first peak and its latency were determined from the global mean-field amplitudes (GMFA). At the latency, 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 neuronal activity spread from the right opIFG into the contralateral hemisphere very early as estimated with MNE. Conclusions: Our combination of experimental settings, data processing tools, and data-analysis methods can be used to evaluate effective connections between speech-related areas and their right-hemispheric homologues. This may be especially important when speech areas cannot be localized with direct stimulation due to the lesion. Because of muscle artifacts, TMS–EEG is often difficult to apply for the study of the initial reactivity and excitability of frontal and temporal cortical areas; however, our methods can make it possible. The combination of our technique and DTI can further elucidate the relation of effective and structural connectivity, which can be crucial when treating patients with rTMS or other types of neuromodulation. nTMS–EEG may be used to select stimulation sites on the cortex when specific neuronal connections in the speech network should be modulated by TMS, for example, in stroke patients.
Themes: Methods, Language Therapy
Method: Neurostimulation