Dear FS team, I have structural data from a training study involving different tDCS groups. I would like to define ROIs (masks) in MNI space corresponding to the approximate cortical area underlying the tDCS electrodes, which were placed on F3&F4 for one group and on P3&P4 in another group (10-20 system positions). I would therefore need to find the approximate centre coordinates, in MNI space, for the F3, F4, P3, P4 electrode positions; however, this is proving challenging.
Other papers that have done this (1 <http://www.sciencedirect.com/science/article/pii/S0960982213007136>, 2 <http://www.jneurosci.org/content/31/43/15284.short>) have obtained coordinates for their electrodes (other positions than mine, unfortunately) using various types of converters, such as Brainstorm <http://neuroimage.usc.edu/neuro/BrainStorm>, Comet <http://cone.hanyang.ac.kr/BioEST/Kor/Comets.html>and the Muenster T2T Converter <http://wwwneuro03.uni-muenster.de/ger/t2tconv/conv3d.html>. However, it's proving very time-costly to get any of these to actually produce MNI coordinates at the cortical (not scalp) level for the electrode positions I mentioned. I suppose a scalp-to-cortex projection would have to be done, but I'm still working out how to do it. Clearly many approximations are involved so these won't be very accurate masks, but I want to at least try to define them first. Also, assuming I find the centre coordinates, how would a surface-based mask, of a certain cortical depth and centred around those coordinates, be created in Freesurfer? Many thanks! Best wishes, Tudor
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