To fill in the gaps in our understanding of resting electrocorticography by identifying normal benign variants on intracranial electroencephalogram (icEEG). 

Approximately 30% of epilepsy patients have drug-resistant epilepsy and may be candidates for epilepsy surgery. icEEG interpretation is crucial for the success of the surgical intervention. Benign variants on icEEG may mimic epileptiform discharges and result in misinterpretations. Understanding such variants is essential to successfully guide the resection of epileptogenic focus while sparing eloquent cortex.

We included 57 studies. The design was prospective cohort (10%), prospective non-randomized controlled (20%), retrospective cohort (50%) and case studies (20%). The stated objectives were to study High frequency oscillations (HFOs) (40%), identify background rhythms (10%), classify epileptic from physiological patterns (30%), describe a questionable pattern (10%), or other (10%). The icEEG was recorded from subdural electrodes/Electrocorticogram (ECOG) (40%), stereo-EEG (SEEG) (20%), a combination of SEEG/ECOG (30%) or other types (10%). Most of the articles studied physiological HFOs (40%), other reported rhythms included: high voltage 14 & 6 Hz, alpha rhythms, small sharp spikes, rhythmic temporal theta bursts of drowsiness, and other physiological patterns. (15.8%) of the studies evaluated sleep icEEG. As we conclude our analysis, we will construct a comprehensive atlas of normal icEEG background rhythms and mimics. 

Our study could increase the accuracy of EEG guided surgical resections by limiting icEEG misinterpretation, which otherwise could lead to resection mistakes and suboptimal surgical outcomes.