Recovery of slow potentials in AC - coupled electrocorticography : 7 application to spreading depolarizations in rat and human cerebral 8 cortex

39 Cortical spreading depolarizations (spreading depressions and peri-infarct 40 depolarizations) are a pathology intrinsic to acute brain injury, generating large negative 41 extracellular slow potential changes (SPCs) which, lasting on the order of minutes, are 42 studied with DC-coupled recordings in animals. The spreading SPCs of depolarization 43 waves are observed in human cortex with AC-coupled electrocorticography (ECoG), 44 though SPC morphology is distorted by the highpass filter stage of the amplifiers. Here, 45 we present a signal processing method to reverse these distortions and recover 46 approximate fullband waveforms from AC-coupled recordings. We constructed digital 47 filters that reproduced the phase and amplitude distortions introduced by specific AC48 coupled amplifiers, and, based on this characterization, derived digital inverse filters to 49 remove these distortions from ECoG recordings. Performance of the inverse filter was 50 validated by its ability to recover both simulated and real low-frequency input test 51 signals. The inverse filter was then applied to AC-coupled ECoG recordings from 5 52 patients who underwent invasive monitoring after aneurysmal subarachnoid hemorrhage. 53 For 117 SPCs, the inverse filter recovered fullband waveforms with morphologic 54 characteristics typical of the negative DC shifts recorded in animals. In comparison to 55 those recorded in the rat cortex with the same analog and digital methods, the negative 56 DC shifts of human depolarizations had significantly greater durations (1:47 vs. 0:45 57 min:sec) and peak-to-peak amplitudes (10.1 vs. 4.2 mV). The inverse filter thus permits 58 the study of spreading depolarizations in humans using the same assessment of fullband 59 DC potentials as in animals, and suggests a particular solution for recovery of biosignals 60 recorded with frequency-limited amplifiers. 61