[FieldTrip] Will different EEG motages have effect on the result of granger connectivity?

["Jörn M. Horschig"]

Dear Weina,

Basically, any montage will cause signal characteristics from the 
sensors used for re-referencing to show up in all other sensors. If you 
use a common average, the signal from any sensor will depend to some 
degree to any other sensor (because common average uses all sensors for 
rereferencing). If you use only Cz, you will obtain a high granger 
causality for any sensors to Cz. This would of course not reflect a real 
brain process, but is just the consequence of substracting the signal 
from Cz from all other sensors. Best would be to use a sensor that you 
will not include in computing granger causality (e.g. a mastoid, or 
choose Cz but then exclude this sensor for further analyses).

Best,
Jörn

On 9/25/2011 7:48 PM, lwn_07 wrote:
> Thanks Jan-Mathijs.  Does it mean if I selected my data segment from 
> mono montage (reference to mastoid), i'd better  calculate the granger 
> causality in mono montage?  Some paper selected Cz as reference, is 
> that OK?
>
> Best regards.
> Weina
>
> ???? iPad
>
> ? 2011-9-25,23:36,jan-mathijs schoffelen <jan.schoffelen at donders.ru.nl 
> <mailto:jan.schoffelen at donders.ru.nl>> ??:
>
>> Hi Weina,
>>
>> Yes, granger causality results will for sure change when you use 
>> different montages. When you replace each measurement (what you call 
>> 'mono-montage') with that measurement minus the average across the 
>> whole recording array (what you call 'average montage') the amount 
>> with which signals can be explained in terms of their own and the 
>> other signals' past will change as well. This most likely leads to 
>> 'granger causality' estimates which just reflect spurious interactions.
>>
>> Best wishes,
>>
>> Jan-Mathijs
>>
>> On Sep 25, 2011, at 1:42 PM, ??? wrote:
>>
>>> Dear all,
>>>   Is anyone knows about that wether different EEG motages (such as 
>>> mono-motage or average montage) have effect on the result of granger 
>>> connectivity?
>>>                                                                                                          
>>> Weina
>>>
>>> _______________________________________________
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>>> fieldtrip at donders.ru.nl <mailto:fieldtrip at donders.ru.nl>
>>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>> Jan-Mathijs Schoffelen, MD PhD
>> Donders Institute for Brain, Cognition and Behaviour,
>> Centre for Cognitive Neuroimaging,
>> Radboud University Nijmegen, The Netherlands
>> J.Schoffelen at donders.ru.nl <mailto:J.Schoffelen at donders.ru.nl>
>> Telephone: +31-24-3614793
>>
>> _______________________________________________
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>
>
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-- 
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group

P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Contact:
E-Mail: jm.horschig at donders.ru.nl
Tel:    +31-(0)24-36-68493
Web: http://www.ru.nl/donders

Visiting address:
Trigon, room 2.30
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NL-6525 EN Nijmegen
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