Neurological prognosis for comatose patients resuscitated after cardiac arrest remains challenging. Functional imaging suggests that altered connectivity of the brain’s default mode network (DMN) could predict poor outcomes. Unfortunately, functional imaging is not easily applicable at the bedside.We proposed a neurophysiological method that assesses DMN function by computing the default EEG reactivity (DER). The method maps continuous EEG to a sequence of recurring oscillatory patterns termed macrostates. We labelled the default EEG macrostate (DEM) as the macrostate with the lowest probability of occurrence during monocular intermittent photic stimulation (IPS).We explored DER in a 4-vessel occlusion model of global cerebral ischemia (GCI) and reperfusion on male Wistar rats. GCI was provoked by electrocautery of vertebral arteries and 5-minute clamping of common carotid arteries under EEG monitoring.With two fronto-occipital leads, we performed EEG acquisition under deep anaesthesia with chloral hydrate. Utilising the ipsilateral lead, we computed DER by determining the decrease in the DEM occurrence probability before and during IPS epochs.Forty-eight hours post-GCI, rats displayed no motor deficiency or seizure activity. DER was consistently lower in the post-GCI group compared to controls (sham surgery) across different anaesthesia depths, from burst suppression to continuous EEG. Visual evoked potentials remained indistinguishable between groups.We showed that DER detects post-ischemic brain injury independently of sedation level. These findings support the ischemic vulnerability of DMN functioning. Considering DER’s reduced montage and bedside applicability, further work should assess DER’s potential as an early neurological prognostic marker in resuscitated comatose patients.