Recording eeg during repetitive trans-cranial magnetic stimulation

This paper discusses several issues related to recording EEG during repetitive trans-cranial magnetic stimulation (rTMS). The objective of recording EEG is to obtain magnetically evoked and event related potentials. The issue of electrode heating is discussed and experimental results presented that show graphite as well as fully notched or "C" silver, gold or silver-silver chloride are suitable for current rTMS protocols. Standard silver or gold cup electrodes may cause excessive scalp heating. Removal or reduction of the magnetically induced stimulus artefact is also discussed. A new system is presented that uses sample and hold circuitry to block most of the artefact allowing the researcher to record ipsi-and contra-lateral evoked potentials occurring within the first few milliseconds of the magnetic stimulus.