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

[dgw]

Hi Andy,

I suspect that if the value is exactly zero, that source location is
likely excluded due to the mindist requirement when calculating your
forward solution. Data from points like these should be excluded from
your analysis (you can convert them to NaN s and then use the
appropriate NaN tools to deal with them).

HTH,
D

On Wed, Oct 1, 2014 at 1:45 PM, Denis-Alexander Engemann
<denis.engemann at gmail.com> wrote:
> 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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