The Listening Zone of Human Electrocorticographic Field Potential Recordings

Abstract

Intracranial electroencephalographic (icEEG) recordings provide invaluable insights into neural dynamics in hu¬mans because of their unmatched spatiotemporal resolution. Yet, such recordings reflect the combined activ¬ity of multiple underlying generators, confounding the ability to resolve spatially distinct neural sources. To empirically quantify the listening zone of icEEG recordings, we computed correlations between signals as a function of distance (full width at half maximum; FWHM) between 8752 recording sites in 71 patients (33 fe¬male) implanted with either subdural electrodes (SDEs), stereo-encephalography electrodes (sEEG), or high- density sEEG electrodes. As expected, for both SDEs and sEEGs, higher frequency signals exhibited a sharper fall off relative to lower frequency signals. For broadband high g (BHG) activity, the mean FWHM of SDEs (6.6 ± 2.5 mm) and sEEGs in gray matter (7.14 ± 1.7 mm) was not significantly different; however, FWHM for low frequencies recorded by sEEGs was 2.45 mm smaller than SDEs. White matter sEEGs showed much lower power for frequencies 17-200 Hz (q < 0.01) and a much broader decay (11.3 ± 3.2 mm) than gray matter electrodes (7.14 ± 1.7 mm). The use of a bipolar referencing scheme significantly lowered FWHM for sEEGs, relative to a white matter reference or a common average reference (CAR). These results outline the influence of array design, spectral bands, and referencing schema on local field potential recordings and source local¬ization in icEEG recordings in humans. The metrics we derive have immediate relevance to the analysis and in¬terpretation of both cognitive and epileptic data.