[Mne_analysis] Interpretation of zero/signs in source current estimations

[acgt2 at cam.ac.uk]

Dear MNE users

This might have come up before, but I have a bit of an interpretation
question - when the source current is estimated, what would 'zero' in the
.stcs mean? Should it be interpreted as an absolute value, where no current
is moving, on average, in or out of the scalp at that source, or it is
relative to some reference current?

I was under the impression that it was some sort of absolute value (ie 'on
average, the net movement of positive ions moving towards or away from the
scalp is zero, in this source'). Then a positive current value (in a
particular source) should be interpreted as the average charge flowing one
way (into the scalp? out?) and negative current values meant it was, on
average, flowing the other direction. But a colleague today suggested that
the zero was relative to a reference: that, due, to neural physiology, there
is always an average positive current inwards/outwards, and it is to this
'baseline' rate that the 'zero' is aligned to. 

Does anyone have any thoughts on which is the correct interpretation? 

Thanks,

Andy

 

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