Technical NoteSimultaneous recording of ECoG and intracortical neuronal activity using a flexible multichannel electrode-mesh in visual cortex

Electrocorticogram (ECoG) is a well-balanced methodology for stably mapping brain surface local field potentials (LFPs) over a wide cortical region with high signal fidelity and minimal invasiveness to the brain tissue. To directly compare surface ECoG signals with intracortical neuronal activity immediately underneath, we fabricated a flexible multichannel electrode array with mesh-form structure using micro-electro-mechanical systems. A Parylene-C-based “electrode-mesh” for rats contained a 6 × 6 gold electrode array with 1-mm interval. Specifically, the probe had 800 × 800 μm2 fenestrae in interelectrode spaces, through which simultaneous penetration of microelectrode was capable. This electrode-mesh was placed acutely or chronically on the dural/pial surface of the visual cortex of Long-Evans rats for up to 2 weeks. We obtained reliable trial-wise profiles of visually evoked ECoG signals through individual eye stimulation. Visually evoked ECoG signals from the electrode-mesh exhibited as well or larger signal amplitudes as intracortical LFPs and less across-trial variability than conventional silver-ball ECoG. Ocular selectivity of ECoG responses was correlated with that of intracortical spike/LFP activities. Moreover, single-trial ECoG signals carried sufficient information for predicting the stimulated eye with a correct performance approaching 90%, and the decoding was significantly generalized across sessions over 6 hours. Electrode impedance or signal quality did not obviously deteriorate for 2 weeks following implantation. These findings open up a methodology to directly explore ECoG signals with reference to intracortical neuronal sources and would provide a key to developing minimally invasive next-generation brain-machine interfaces.

Graphical Abstract580Research highlights► Mesh-form micro electrode array of 20µm-thickness was developed for ECoG recording. ► 'Fenestrae' in mesh improved fitting and allowed simultaneous use of other probes. ► VEPs were stably recorded in both acute and chronic preparations of rat V1. ► Qualities of ECoG signal from electrode mesh were comparable to intracortical LFP. ► Stimulated eye was decoded from mesh ECoG with a single-trial accuracy of nearly 90%.