[wineeg] Drop in amplitude right hemisphere?

  • From: Joe Siri Ekgren <vennskap@xxxxxxxxx>
  • To: wineeg@xxxxxxxxxxxxx
  • Date: Thu, 21 Aug 2003 14:36:03 +0200

Dear Listmembers,

I have an EEG with EO/EC/task that with a referential montage (linked 
ears) that shows low amplitude in F8-T4-T6 with lowest amplitude in 
T4.The topo maps of the qEEG show a black brim along this 
localization in all bandranges. The impedance was between 1- 2.5 kOhm 
in all leads.

A different montage,  averaged reference shows less of the brim but 
there still is a decrease in amplitude compared to right side.

I used the electro-cap. The same trend is seen when using another set 
of electrodes in a different eeg 3 months ago. No other patients have 
this trend.

In theory what might cause this?
Will temporal cortical activity picked up at the right earlobe 
diminish the activity seen in the nearby electrodes, especially in a 
referential montage? An EKG artefact found in the other leads also 
vanishes in F8-T4-T6.

I am thinking of alternatives
        increased skull thickness,
        a slow expansive process (hematoma, tumour) between the 
cortex and the skull at T4

Can one have problems with electrode function even with a good impedance?

Also, there might be some hardware issue since A2 almost always has a 
kOhm or so higher impedance than A1. A2 was higher than A1 even after 
keeping the electrodes in place and trading the place of the A1 jack 
with the A2 jack. I expected the A1 to show the higher impedance but 
the A2 remained higher than A1. Is there an amplifier problem in all 
of this.

Questions, questions...

Thank you in advance for any help and ideas.


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