The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

DC-EEG for Routine Clinical Use: Methods and Clinical Impact

Pekka Tallgren

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 15th of December, 2006, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-6956-2)   [1058 KB]
Dissertation is also available in print (ISBN 951-22-6955-4)


The aim of this work was to map the requirements of extending the EEG recording bandwidth down to direct current (DC). Standard methods of clinical electroencephalography (EEG) are based on AC-coupled recording devices with a typical high-pass cut-off frequency at 0.5 Hz. Amplifier and electrode technology together with millivolt scale skin originated signals, have all rejected the recording of EEG signals down to DC. In the early days of EEG, high-pass filtering was introduced to prevent saturation of the amplifier, thereby making DC-stability an irrelevant topic in electrode and amplifier development. Occasionally, researchers have recorded EEG down to DC, but the needed technology and method(s) have never been widely known. This thesis presents solutions to overcome the above mentioned problems.

Early invasive experiments have shown that a significant potential difference prevails between the brain and other body tissues. However, the clinical significance and the potential diagnostic applications of infra-slow EEG signals have been a subject of little interest. This study was carried out in order to develop a method that would, for the first time, make routine bedside recording of DC-EEG possible, and to apply it in the clinic. The work included construction of a multi-channel DC-EEG amplifier that meets medical safety specifications as well as the data acquisition and analysis software. Different types of commercially available EEG electrodes and gels were investigated. The obtained results clearly point to the combination of a chloride-containing gel and silver|silverchloride (Ag|AgCl) electrodes as a prerequisite of adequate DC-EEG recording. Due to the fact that significant infra-slow skin-borne signals could contaminate DC-EEG, the means of short-circuiting the signal source in skin were studied to find one that is practical in clinical applications. Two studies were carried out to shed light on the role of the blood-brain barrier and brain haemodynamics in mechanisms underlying DC-shifts.

Finally, the developed methods were applied on preterm infants and on patients with temporal lobe epilepsy. Very slow activity patterns of potential diagnostic value were observed in preterm EEG, and DC-shifts were found useful in lateralization of the origin of temporal lobe seizures. Taken together, the results indicate that DC-EEG can now for the first time be applied as a routine bedside method, and that infra-low frequency EEG data have a promising diagnostic value.

This thesis consists of an overview and of the following 6 publications:

  1. Voipio J, Tallgren P, Heinonen E, Vanhatalo S, Kaila K. Millivolt-scale DC shifts in the human scalp EEG: evidence for a nonneuronal generator. Journal of Neurophysiology, 2003, 89: 2208-2214. © 2003 American Physiological Society. By permission.
  2. Vanhatalo S, Tallgren P, Becker C, Holmes MD, Miller JW, Voipio J, Kaila K. Scalp-recorded slow EEG responses generated in response to hemodynamic changes in the human brain. Clinical Neurophysiology, 2003, 114: 1744-1754. © 2003 International Federation of Clinical Neurophysiology and © 2003 Elsevier Science. By permission.
  3. Tallgren P, Vanhatalo S, Kaila K, Voipio J. Evaluation of commercially available electrodes and gels for recording of slow EEG potentials. Clinical Neurophysiology, 2005, 116: 799-806. © 2005 International Federation of Clinical Neurophysiology and © 2005 Elsevier Science. By permission.
  4. Tallgren P. DC-stable electrode-skin interface for human EEG recordings. Helsinki University of Technology, Applied Electronics Laboratory, Series E: Electronic Publications, 2005, E5: 3-12. © 2005 by author.
  5. Vanhatalo S, Tallgren P, Andersson S, Sainio K, Voipio J, Kaila K. DC-EEG discloses prominent, very slow activity patterns during sleep in preterm infants. Clinical Neurophysiology, 2002, 113: 1822-1825. © 2002 International Federation of Clinical Neurophysiology and © 2002 Elsevier Science. By permission.
  6. Vanhatalo S, Holmes MD, Tallgren P, Voipio J, Kaila K, Miller JW. Very slow EEG responses lateralize temporal lobe seizures: an evaluation of non-invasive DC-EEG. Neurology, 2003, 60: 1098-1104. © 2003 Lippincott Williams & Wilkins. By permission.

Keywords: DC-EEG, slow oscillations, EEG electrodes, GSR

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2006 Helsinki University of Technology

Last update 2011-05-26