Abstract
Combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) can be used to analyze cortical reactivity and connectivity. However, the effects of corticospinal and peripheral muscle activity on TMS-evoked potentials (TEPs) are not well understood. The aim of this paper is to evaluate the relationship between cortico-spinal activity, in the form of peripheral motor-evoked potentials (MEPs), and the TEPs from motor areas, along with the connectivity among activated brain areas. TMS was applied to left and right motor cortex (M1), separately, at motor threshold while multi-channel EEG responses were recorded in 17 healthy human subjects. Cortical excitability and source imaging analysis were performed for all trials at each stimulation location, as well as comparing trials resulting in MEPs to those without. Connectivity analysis was also performed comparing trials resulting in MEPs to those without. Cortical excitability results significantly differed between the MEP and no-MEP conditions for left M1 TMS at 60 ms (CP1, CP3, C1) and for right M1 TMS at 54 ms (CP6, C6). Connectivity analysis revealed higher outflow and inflow between M1 and somatosensory cortex bi-directionally for trials with MEPs than those without for both left M1 TMS (at 60, 100, 164 ms) and right M1 TMS (at 54, 100, and 164 ms). Both TEP amplitudes and connectivity measures related to motor and somatosensory areas ipsilateral to the stimulation were shown to correspond with peripheral MEP amplitudes. This suggests that cortico-spinal activation, along with the resulting somatosensory feedback, affects the cortical activity and dynamics within motor areas reflected in the TEPs. The findings suggest that TMS-EEG, along with adaptive connectivity estimators, can be used to evaluate the cortical dynamics associated with sensorimotor integration and proprioceptive manipulation along with the influence of peripheral muscle feedback.
Highlights
The functional activity of multiple areas of the brain acting simultaneously in concert is the basis for the performance of any behavior
The present results demonstrate that the spread of the activations for both left and right M1 Transcranial magnetic stimulation (TMS) is from the stimulated motor area to central motor and parietal areas, along with areas in the middle, superior and inferior frontal lobe
Regarding the origins of each latency, the activations shown within the stimulated area at 30ms and 44ms for left M1 stimulation are likely due to excitatory activity intrinsic to this area [46], though previous studies have suggested that the 30ms latency could reflect the activation of subcortical pathways, to the thalamus and basal ganglia, which include reciprocal connections back to cortical areas [21]
Summary
The functional activity of multiple areas of the brain acting simultaneously in concert is the basis for the performance of any behavior. Simultaneous TMS and scalp electroencephalography (EEG) can be used to assess cortical reactivity and connectivity by directly stimulating a cortical region and evaluating the spatial and temporal propagation of the evoked activity. In this way, previous TMS-EEG studies have highlighted the promise of this combined approach, demonstrating the spatiotemporal spread of the TMS-evoked activity to a network of related cortical areas over time [7,8,9]. Former TMS/EEG studies of the motor network, in particular, have revealed that TMS-evoked activity spreads from the stimulation site to contralateral motor, sensory, pre-motor, and frontal areas over time [8,10,11,12,13]. While former studies have provided a basis for understanding the expected topographical responses to stimulation of various brain areas, several questions remain unanswered
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
