Abstract Body: Background: Ischemic stroke remains a major cause of mortality and disability, significantly affecting patient quality of life despite advancements in treatment. Analysis of electroencephalogram (EEG) is crucial for assessing brain activity, offering insights into different physiological states. While ischemic stroke induces notable changes in EEG signals, the specific patterns and their implications are not fully understood. Here, we use the Hilbert-Huang transform (HHT) to analyze the EEG signal before, during, and after ischemic stroke in rats.

Methods: The standard intraluminal filament middle cerebral artery (MCA) occlusion model was used to induce ischemic stroke in 16 male Sprague Dawley rats (8-10 weeks old). A suture was advanced into the internal carotid artery to occlude the MCA for 1 hour, followed by 3 hours of reperfusion (Fig. 1). Cerebral infarction was confirmed post-surgery using TTC staining technique. EEG signals were continuously recorded throughout the procedure. We applied the Hilbert-Huang Transform (HHT) to analyze the EEG signals. HHT involves two main steps: 1) empirical mode decomposition (EMD), to decompose the EEG signal into a set of intrinsic mode functions (IMF); 2) the Hilbert Transform, which is applied to each IMF to obtain analytic signals. These analytic signals are represented in the complex plane, where they often exhibit circular or elliptical forms (Fig. 2). The area of these circles in the complex plane reflects unique information on variations in the signal properties. We computed the HHT area metric for the first 4 IMFs at three timepoints: baseline, 1 hour post-MCA occlusion (pre-reperfusion), and 3 hours post-reperfusion. 2-minute EEG recordings were used at each timepoint for the HHT analysis.

Results and Conclusions: Significant changes (P<0.05) were observed in the HHT area metric after the ischemic stroke occurrence (Fig. 3). For all IMFs, the HHT area metric reduced significantly from baseline to pre-MCA-reperfusion. However, it increased significantly from pre-MCA-reperfusion to 3 hours post-reperfusion. Comparing the baseline with post-reperfusion timepoint, significant reduction was still observed. Our results showed for the first time that the HHT can effectively analyze EEG signals to capture changes induced by ischemic stroke. Our new finding highlights the potential of HHT in providing insights into stroke-related changes in EEG, offering a valuable tool for detection or monitoring ischemic stroke.