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. -- Joe