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This Article Full Text Full Text (PDF) Supplemental Appendix Buy All Versions of this Article: 102/4/2563    most recent 00345.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Hartings, J. A. Articles by Fabricius, M. PubMed PubMed Citation Articles by Hartings, J. A. Articles by Fabricius, M.

INNOVATIVE METHODOLOGY

Recovery of Slow Potentials in AC-Coupled Electrocorticography: Application to Spreading Depolarizations in Rat and Human Cerebral Cortex

¹Division of Psychiatry and Neuroscience, Walter Reed Army Institute of Research; ²Undersea Medicine Department, Naval Medical Research Center, Silver Spring, Maryland; ³Center for Stroke Research, Charité Universitätsmedizin Berlin, Berlin, Germany; and ⁴Department of Clinical Neurophysiology, Glostrup Hospital, Copenhagen, Denmark

Submitted 17 April 2009; accepted in final form 29 May 2009

ABSTRACT

Cortical spreading depolarizations (spreading depressions and peri-infarct depolarizations) are a pathology intrinsic to acute brain injury, generating large negative extracellular slow potential changes (SPCs) that, lasting on the order of minutes, are studied with DC-coupled recordings in animals. The spreading SPCs of depolarization waves are observed in human cortex with AC-coupled electrocorticography (ECoG), although SPC morphology is distorted by the high-pass filter stage of the amplifiers. Here, we present a signal processing method to reverse these distortions and recover approximate full-band waveforms from AC-coupled recordings. We constructed digital filters that reproduced the phase and amplitude distortions introduced by specific AC-coupled amplifiers and, based on this characterization, derived digital inverse filters to remove these distortions from ECoG recordings. Performance of the inverse filter was validated by its ability to recover both simulated and real low-frequency input test signals. The inverse filter was then applied to AC-coupled ECoG recordings from five patients who underwent invasive monitoring after aneurysmal subarachnoid hemorrhage. For 117 SPCs, the inverse filter recovered full-band waveforms with morphologic characteristics typical of the negative DC shifts recorded in animals. Compared with those recorded in the rat cortex with the same analog and digital methods, the negative DC shifts of human depolarizations had significantly greater durations (1:47 vs. 0:45 min:sec) and peak-to-peak amplitudes (10.1 vs. 4.2 mV). The inverse filter thus permits the study of spreading depolarizations in humans, using the same assessment of full-band DC potentials as that in animals, and suggests a particular solution for recovery of biosignals recorded with frequency-limited amplifiers.