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Scalp ultra-low frequency electroencephalography

University of British Columbia

Electrical activities of the brain include the regular electroencephalogram (AC-EEG, typically 0.5Hz<f<70 Hz) as well as slow potentials (DC-EEG, f < 0.1Hz). According to recent studies, slow or DC potentials displacements (DC-EEG) are informative features, highly associated with a pathology of diverse neurological disorders. This valuable data is usually neglected due to physiological (e.g., eye movement and respiration) and non-physiological (electrode movement and characteristics) artifacts that are present in the data recordings. Spreading depression (SD) is a negative DC potential and remains one of the most significant EEG patterns in DC-EEG. SD is a major, transient, and localized relocation of ions between the extracellular and intracellular spaces. It is associated with the pathophysiology of various neurological disorders, as well as the conduct of many voluntary tasks in healthy human subjects. This wave has been recorded during electrocorticography (ECoG), and technical difficulties relevant to this invasive technique have hampered the study of SD-related disorders in human subjects. Therefore, we have proposed a novel method to record the negative DC potential non-invasively. The novel method consists of a newly designed ultra-low noise AC/DC-EEG amplifier, a specific electrode-electrolyte combination, and a developed electrode-electrolyte-skin electrical model in the ultra-low frequency range. Further, using our new system, we successfully captured SD waves with simultaneous non-invasive electroencephalography and invasive ECoG recordings in rats. We then compared the invasive and non-invasive recorded SD waves to obtain further insight into structures of the SD recorded from the surface of the scalp. This comparison revealed that SD recorded from the scalp surface indeed reflects the SD recorded invasively from the neocortex. We utilized a variety of signal processing techniques to analyze the resulting data, including spectral analysis, bi-spectral analysis, pattern distribution, relative spectral power, and multivariable Gaussian fit analysis. The results demonstrate that cortical negative DC shifts (SD) induced by KCl injection can be measured on the intact skin surface overlying the neocortex. The DC potentials at the cortical surface reveal a highly correlated homogeneity with the SD measured at the surface of the scalp.

Text

2018-07-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/58417

Biomedical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/