Second, we posit that discordant theta findings may be exacerbated by the referencing schemes that researchers preferentially use to with scalp EEG vs. intracranial EEG. Whereas scalp EEG most commonly uses an average reference scheme or a single electrode as a common reference (e.g. on the mastoid), intracranial EEG is mostly referenced with a bipolar scheme to eliminate local noise that similarly affects neighboring electrodes. This choice of reference amplifies the difference in spatial resolution between scalp EEG and intracranial EEG, since bipolar referencing acts as a spatial high-pass filter by selectively removing correlated measurements across spatially close electrodes. These correlated measurements include both spatially distributed noise and spatially distributed signals. We know that low frequency activity (where low-frequency refers to the temporal domain) typically is observed with a low spatial frequency, meaning that it is correlated across large areas of cortex [71,72]. A bipolar referencing scheme, as commonly used with intracranial data, should therefore eliminate spatially distributed low-frequency effects in the majority of electrodes, and only reveal those effects at the bipolar channels that border the true effect (i.e.
