ICA with averaged data

[Niki Ray]

Hi,
  I'm very new to fieldtrip. I have three questions. I have collected MEG
data from patients with a deep brain stimulator implanted. I'd like to do an
ICA to reject the stimulator related artifacts. Sometimes the stimulator is
on and sometimes off. So my first question is, do i combine all the data
together and then perform the ICA, or do i do different ICA analyses for
each condition(on and off stimulation), and hence reject different
components for each condition?  

 One possibility for deciding wich of the artifacts were related to the
stimulator was to use the example matlab script you provide for rejecting
ECG components. Some of the channels (about 13, i'm using a ctf 275 system)
have a lot of very distinct artifact that is obviously from the stimulator,
so i wanted to use one of these channels as the "ECG" channel. Is this
sensible, or not?? 

  Finally, I've been getting conflicting advice about whether it is okay to
first average data, and then perform an ICA. What do you suggest is the
right thing to do?

Many thanks!
Niki