Columnar localization and laminar origin of cortical surface electrical potentials
Electrocorticography (ECoG) methodologically bridges basic neuroscience and understanding of human brains in health and disease. However, the localization of ECoG signals across the surface of the brain and the spatial distribution of their generating neuronal sources are poorly understood. To address this gap, we recorded from rat auditory cortex using customized microECoG, and simulated cortical surface electrical potentials with a full-scale, biophysically detailed cortical column model. Experimentally, microECoG-derived auditory representations were tonotopically organized and signals were anisotropically localized to 200 micrometers, i.e., a single cortical column. Biophysical simulations reproduce experimental findings, and indicate that neurons in cortical layers V and VI contribute ~85% of evoked high-gamma signal recorded at the surface. Cell number and synchronicity were the primary biophysical properties determining laminar contributions to evoked microECoG signals, while distance was only a minimal factor. Thus, evoked microECoG signals primarily originate from neurons in the infragranular layers of a single cortical column.