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

Denis-Alexander Engemann denis.engemann at gmail.com
Wed Oct 1 13:45:48 EDT 2014
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Hi Andy,

2014-10-01 19:40 GMT+02:00 <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?
>

do you mean literally zero?
Do you talk of individual source estimates or did you morph the estimates
to the average brain?

-Denis

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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