Target muscle activation level was 10±3% of RMS MVC when active and < 10 µV at rest. TMS Delivered at 120% active motor threshold (AMT) for each muscle. Each map used 120-150 pseudorandomly placed stimulations [3]. Data collection and analysis Coil and head 3-D positions and orientations, and MEPs, at times of TMS stimulation were saved using custom soft­ ware*. 3-D stimulation locations were fitted to a sphere, then represented in 2-D spherical coordinates. The cloud of MEP values & positions was resam­ pled onto a regular grid (MEPest) using radial ba­ sis function interpolation. Is muscle co-activation preferentially driven by overlapping cortical map regions? Matthew J Ward, John Cirillo, Angus J C McMorland Department of Exercise Sciences, University of Auckland Overlapping cortical muscle maps: a substrate for synergistic activation? Fast, optically tracked, dual-muscle TMS mapping Contact information Dr Angus McMorland a.mcmorland@auckland.ac.nz * https://github.com/mwar136/TMS-map­ ping-and-analysis References head marker coil marker on end AD electrode FDI electrode Optical tracking (Polaris, NDI) of coil and head during mapping and recording of EMG from AD and FDI. Tasks Repetitive actions, in time with a metronome (4 - 5.5 s per stim): 1) thumb-index finger pinch; FDI map only 2) push peg with palm, from shoulder; AD map only 3) combined - pinch & push; map both muscles AD (blue) and FDI (red) muscle maps during in­ dependent (A) and synergy (B) movements. Maps show large overlap, particularly of highly excitable areas. Centre of gravity (COG) of FDI (red square) is lateral of AD COG (blue triangle) in both maps. Position is relative to Cz. FDI AD 40 -20 -80 -10 ML (mm to Cz) AP (mm to Cz) Motor cortical representations of proximal and distal muscles, such as anterior deltoid (AD) and first dorsal interosseous (FDI), overlap [1, 2]. Motor evoked potential (MEP) amplitude in response to transcranial magnetic stimulation (TMS) of motor cortex. 1. H. Devanne et al., The comparable size and overlapping nature of upper limb distal and proximal muscle representations in the human motor cortex. Eur. J. Neurosci. 23, 2467–2476 (2006). 2. J.-A. Rathelot, P. L. Strick, Muscle representation in the macaque motor cortex: an anatomical perspective. Proc. Natl. Acad. Sci. U. S. A. 103, 8257–8262 (2006). 3. M. van de Ruit, M. J. L. Perenboom, M. J. Grey, TMS brain mapping in less than two minutes. Brain Stimul. 8, 231–239 (2015). 4. H. Devanne, L. G. Cohen, N. Kouchtir-Devanne, C. Capaday, Integrated motor cortical control of task-related muscles during pointing in humans. J. Neurophysiol. 87, 3006–3017 (2002). Overlap of cortical muscle maps may facilitate synergistic co-activation of muscles. This study tests the hypothesis: During synergistic tasks, overlapping portions of the muscle maps are preferentially activated compared to non-overlapping regions. Participants Participant Age (Years) Sex Laterality Index (%) AD AMT (%MSO) FDI AMT (%MSO) 1 22 F 100 58 38 2 21 M 100 78 40 3 22 M 67 68 36 4 32 M 100 46 34 5 21 M 100 33 28 6 22 M 100 66 45 7 22 M 100 70 46 8 31 F 100 60 33 9 21 F 67 69 30 10 23 M 100 66 25 11 21 M 71 60 44 12 21 F 100 68 38 13 23 M 100 63 46 Mean 23.2 69% M 92.7 61.9 37.2 SD 3.75 14.0 3.2 1.9 1. No evidence for preferential excitation of over­ lapping regions of muscle maps for synergistic activation. 2. No change in overall excitability in the syner­ gistic task suggests that FDI and AD are inde­ pendent in terms of co-activation, which has im­ plications for horizontal connectivity (excitatory or disinhibitory) between the networks associated with these muscles. 3. FDI may be ‘special’; previous studies suggest coactivation of FDI and ECR is not similarly inde­ pendent [4]. All subjects were healthy and right-handed. As expected, active motor threshold was lower (above), and MEP amplitude was higher (below) in FDI than AD, because direct corticospinal projections innervate distal muscles more than proximal.