Drifting of record during experiment

[Johan_P]

Hi all,
I'm using biosemi active2 system with 16 electrodes + 8 external.
I'm doing CNV experiment and manage to obtain quite good result but I lose a lot of data due to the drifting of the active electrode. It's not a very big drifting but my baseline is not on zero and not stable. So for some stimulation, I have drifting through the positive values and the CNV activity (which should be in the negative value) is lost in this drifting. I can't take these kind of data into account.

Could you have some tips regarding this problem ? Do you know what could be the origin? I know that temperature, perspiration, stress could change a bit the drifting, but there also could be other more controllable factor that I don"t know...

Thanks,
Johan

[Coen]

Raw data on file is always DC (regardless of display filters during recording), apply an high-pass filter during analysis.

Best regards, Coen (BioSemi)

[Johan_P]

Thanks Coen,
I already use a passband filter between 0.03Hz to 30Hz. The drifting is still here.
For example, after filtering, cleaning and epoching you can obtain something like the picture below


What do you think ?

Johan

[Coen]

Excessive drift is usually caused by perspiration. Try organize a cool and comfortable environment for the subjects during the experiment.

Best regards, Coen (BioSemi)