Infralow Activity on Intracranial EEG: A Systematic Review: Characteristics, Recording Methods and Predictive Value of the Zone to Remove

<b>Objectives</b>We aimed to clarify the occurrence pattern of icDCs (ictal direct-current shifts), its recording parameters, polarity, and amplitude and to elucidate whether icDCs correlated with histology and the resection of the core area of icDCs is associated with favorable outcomes. <b>Methods</b> We carried out a systematic review according to the PRISMA statement. We searched for studies describing intracranial direct current shift, intracranial slow potential shift (SPS), or intracranial infralow activity AND surgical outcome. <b>Results</b> There is a marked heterogenicity in the recording parameters of icDCs, and in the method of intracranial evaluation (SEEG, subdural electrodes or both); icDCs can be obtained in more than 90% of patients with epilepsy evaluated with intracranial electrodes and in more than 90% of the seizures; icDCs is an electrical phenomenon with very high amplitude, with positive or negative polarity and prolonged duration, seen before or during seizure onset; IcDCs are best recorded with a time constant of 10 s, and setting LFF at 0.01 to 0.016 Hz and variable HFF; it seems preferable to evaluate them with an epoch of 300 s. IcDCs are not specific to any subjacent pathology. icDCs increases the probability of being seizure-free by 30.5. <b>Conclusion</b> Infralow activity can be assessed during intracranial recording with sEEG or subdural electrodes. Infralow activity is a prolonged baseline shift, with a very high amplitude appearing before or with the seizure onset. This might not be related to the subjacent pathology, but it helps delineate the zone to remove.