Automatic identification and removal of scalp reference signal for intracranial eegs based on independent component analysis

Sanqing Hu, Matt Stead, Gregory A. Worrell

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


The pursuit of an inactive recording reference is one of the oldest technical problems in electroencephalography (EEG). Since commonly used cephalic references contaminate EEG and can lead to misinterpretation, extraction of the reference contribution is of fundamental interest. Here, we apply independent component analysis (ICA) to intracranial recordings and propose two methods to automatically identify and remove the reference based on the assumption that the scalp reference is independent from the local and distributed intracranial sources. This assumption, supported by our results, is generally valid because the reference scalp electrode is relatively electrically isolated from the intracranial electrodes by the skull's high resistivity. We point out that the linear model is underdetermined when the reference is considered as a source, and discuss one special underdetermined case for which a unique class of outputs can be separated. For this case most ICA algorithms can be applied, and we argue that intracranial or scalp EEGs follow this special case. We apply the two proposed methods to intracranial EEGs from three patients undergoing evaluation for epilepsy surgery, and compare the results to bipolar and average reference recordings. The proposed methods should have wide application in quantitative EEG studies.

Original languageEnglish (US)
Pages (from-to)1560-1572
Number of pages13
JournalIEEE Transactions on Biomedical Engineering
Issue number9
StatePublished - Sep 2007


  • Blind source separation
  • Coherence and synchrony
  • Electroencephalography (EEG)
  • FastICA algorithm
  • Linear model
  • Scalp reference signal
  • Underdetermined mixing matrix

ASJC Scopus subject areas

  • Biomedical Engineering


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