Comparison of subdural and subgaleal recordings of cortical high-gamma activity in humans

- We compare high-gamma (70-110 Hz) brain signals recorded with subdural and subgaleal electrodes.
- Signal attenuation is modeled with linear and 1-pole filter transfer functions.
- Findings suggest that the skull does not distort or selectively filter signals.

ObjectiveThe purpose of this study is to determine the relationship between cortical electrophysiological (CE) signals recorded from the surface of the brain (subdural electrocorticography, or ECoG) and signals recorded extracranially from the subgaleal (SG) space.MethodsWe simultaneously recorded several hours of continuous ECoG and SG signals from 3 human pediatric subjects, and compared power spectra of signals between a differential SG montage and several differential ECoG montages to determine the nature of the transfer function between them.ResultsWe demonstrate the presence of CE signals in the SG montage in the high-gamma range (HG, 70-110 Hz), and the transfer function between 70 and 110 Hz is best characterized as a linear function of frequency. We also test an alternative transfer function, i.e. a single pole filter, to test the hypothesis of frequency dependent attenuation in that range, but find this model to be inferior to the linear model.ConclusionsOur findings indicate that SG electrodes are capable of recording HG signals without frequency distortion compared with ECoG electrodes.SignificanceHG signals could be recorded minimally invasively from outside the skull, which could be important for clinical care or brain-computer interface applications.