Resources about noninvasive EEG for BCI purposes


I realized although many resources are available about EEG properties and processing in a BCI loop, I have some questions about it which are not easily answered without a deep search in the scientific literature. So I thought about asking here

Do you recommend any quality resource on the practical limits and advantages of EEG use for BCI?

Some questions I have right now:

  • Why are there not many studies with high density of electrodes? I usually see the 10-20 system being used, but would there be a use if electrodes were positioned inbetween, or at even smaller separation?
  • Can a classifier discriminate feet MI or individual fingers MI from EEG signal? I saw some papers about it, but another review said it is impossible (maybe meaning we could never have 100% classification accuracy?). Is it a proven statement, or an heuristic observation?