RESEARCH ARTICLE


Spectral Pattern Analysis of Propofol Induced Spindle Oscillations in the Presence of Auditory Stimulations



Murat Ozgoren1, 2, *, Onur Bayazit1, Necati Gokmen1, 3, Adile Oniz1, 2
1 Department of Biophysics, Faculty of Medicine, Dokuz Eylul University, Izmir Turkey
2 Brain Dynamics Research Center, Dokuz Eylul University, Izmir, Turkey
3 Department of Anesthesiology, Faculty of Medicine, Dokuz Eylul University, Izmir Turkey


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© Ozgoren et al; Licensee Bentham Open

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the Department of Biophysics, Faculty of Medicine, Dokuz Eylul University, Izmir Turkey; T Tel: +90 (232) 4124485; Fax: +90 (232) 2794044; E-mail: murat.ozgoren@deu.edu.tr


Abstract

This study’s primary objective is to analyze human EEG spindle oscillations during propofol-induced anesthesia and to address possible activation sources. Such an analysis also has a secondary role of investigating the short- term spectral patterns and their functional role.

Artifact-free epochs of spindle activations were selected from the electroencephalograms of patients undergoing propofol anesthesia. Power spectral analysis and source localization using standardized low-resolution-brain-electromagnetic-tomography (sLORETA) were performed. Additionally, spectrograms were obtained by means of using the Complex Morlet-based algorithm. In order to highlight the functional properties, auditory stimulations were conducted during the propofol administration. The loss of consciousness was reached at a level of 0.8-1.2 µg/mL, which also provided distinct spindle oscillations in the continuous EEG. The un-evoked (spontaneous) and evoked (auditory) conditions were examined across non-medicated and medicated conditions (propofol). The propofol administration resulted in appearance of 12-14 Hz spindle activity mostly localized in BA6, BA9, BA10, BA21, BA24 and BA37 areas. The presence of auditory stimulations slightly shifted these maximum activities to different locations. Between the medicated and non-medicated conditions, there was a significant reduction of spindle activity, which was pinpointed to BA7 (precuneus area). The findings indicate that spindle oscillations may have a dual nature. That is, spindle oscillations may be activity dependent and disruptive for large-scale information processing networks in the brain. Hence, the study of spindle oscillation may provide a basis for understanding the short-term spectral patterns of human EEG.

Keywords: Spindle oscillations, BA7, precuneus, consciousness, sLORETA, propofol, anesthesia.