Table 2.
Scalp locations of M1-FDI, S1-index, and C3/C4 relative to vertex (Cz), from seven independent sources of evidence
| Location Relative to Vertex (Cz) mean ± SD cm (min:max) |
||||||
|---|---|---|---|---|---|---|
| Left hemisphere |
Right hemisphere |
|||||
| Location and source | N | Lateral | Anterior | N | Lateral | Anterior |
| M1-FDI, TMS studies (2011–2018) | 56 | −5.2 ± 0.8 (−7.0:-3.0) | 0.4 ± 0.9 (−2.6:2.0) | 14 | 5.2 ± 0.9 (3.5:7.5) | 0.5 ± 0.9 (−1:1.8) |
| S1-index, TMS meta-analysis (N = 96 studies, 1991–2017)* | 1693 | −5.9 ± 0.9 (−8.2:-4.4) | −1.3 ± 1.0 (−3.6:0.4) | |||
| C3/C4, head measurements (2016–2018) | 101 | −7.2 ± 0.3 (−7.8:-6.6) | 0 | |||
| S1-index, fMRI meta-analysis (LH N = 425; RH N = 316, 54 studies, 1999–2017), projected onto scalp in MRI | 100 | −6.8 ± 0.4 (−9.4:-5.7) | −0.6 ± 0.7 (−2.3:2.2) | 100 | 6.9 ± 0.4 (6.1:9.8) | −0.6 ± 0.8 (−2.3:1.8) |
| S1-index, Experiment 1 (2014–2015) | 10 | −7.5 ± 0.7 (−9.0:-7.0) | 2.6 ± 0.3 (2.0:3.0) | |||
| S1-index, Experiment 2 (2017) | 12 | −7.0 ± 1.1 (−8.8:-5.2) | 0.8 ± 1.0 (−1.5:2.1) | |||
| S1-index, fMRI study (N = 20, 2012–2014), group contrast projected onto scalp in navigated TMS studies (2016–2018) | 11 | −7.8 ± 0.9 (−10.0:-6.7) | −0.2 ± 1.0 (−1.5:1.4) | 9 | 8.4 ± 1.1 (7.0:10.3) | −0.4 ± 0.6 (−1.1:0.3) |
fMRI, functional magnetic resonance imaging; LH, left hemisphere; M1-FDI, first dorsal interosseus muscle’s primary motor cortex representation; RH, right hemisphere; S1-index, representations of the index finger; TMS, transcranial magnetic stimulation.
*
Collapsed across hemispheres, and using assumed scalp locations for M1-FDI representations where not reported.