Intracranial EEG referencing for large-scale category-selective mapping in the human ventral occipito-temporal cortex

Intracranial EEG (iEEG) is increasingly used in many fields of human cognitive neuroscience since it offers a unique opportunity to directly record brain activity from awake humans at a high spatial and temporal resolution. However, little is known about the influence of the reference montage on the spatial and temporal characteristics of iEEG activity. Here, we compare the spatial and temporal profiles of neural activity for five reference montages (scalp reference, common average, zero reference, local Bipolar, and Laplacian) applied to a large dataset of depth electrodes (StereoElectroEncephaloGraphy, SEEG) recordings across the human ventral occipito-temporal cortex (VOTC, N individual brains = 77). Frequency-tagging is used for objective identification and quantification of both low- (<30 Hz) and high-frequency (40-160 Hz) face-selective neural activity. For low-frequency responses, similar spatial distributions and time-courses of significant face-selective contacts and of face-selective amplitudes are found across the five reference montages, although the latter two local reference montages enhance face selectivity along the fusiform gyrus until the anterior temporal lobe. However, they also reduce the right hemisphere dominance, a hallmark of face-selective neural activity, and increase the number of significant contacts in the white matter. For high-frequency responses, similar spatial distributions and time-courses of significant face-selective contacts and of face-selective amplitudes are found for all references, except for the scalp reference (SCA), which enhances face selectivity in lateral and medial regions of the anterior VOTC. However, SCA also increases the number of significant contacts in the white matter. Thus, specificities of each electrode montage should be considered before choosing an iEEG reference, according to the research question, the anatomical region, the type of analyses, and the responses frequency range.