Abstract
Cortical propagating waves have recently attracted significant attention by the neuroscience community. These travelling waves have been suggested to coordinate different brain areas and play roles in assisting neural plasticity and learning. However, it is extremely challenging to record them with very fine spatial scales over large areas to investigate their effect on neural dynamics or network connectivity changes. In this work, we employ high-density porous graphene microelectrode arrays fabricated using laser pyrolysis on flexible substrates to study the functional network connectivity during cortical propagating waves. The low-impedance porous graphene arrays are used to record cortical potentials during theta oscillations and drug-induced seizures in vivo. Spatiotemporal analysis on the neural recordings reveal that theta oscillations and epileptiform activities have distinct characteristics in terms of both synchronization and resulting propagating wave patterns. To investigate the network connectivity during the propagating waves, we perform network analysis. The results show that the propagating waves are consistent with the functional connectivity changes in the neural circuits, suggesting that the underlying network states are reflected by the cortical potential propagation patterns.
Highlights
MethodsFabrication process of the porous graphene electrode array
We demonstrated that the high-density porous graphene electrode arrays provide high spatiotemporal resolution to capture the rich dynamics of the propagating cortical waves
The flexibility of the array and the low impedance of porous graphene electrodes enabled the recording of cortical potentials with high fidelity
Summary
Fabrication process of the porous graphene electrode array. We used a laser engraving and cutting system (PLS6.75, Universal Laser Systems Inc.) equipped with a 10.6 μm wavelength CO2 laser to irradiate polyimide films (50 μm thick, Kapton). The polyimide was first rinsed with acetone, isopropyl alcohol, and deionized water for cleaning, and later de-moisturized with a hotplate at 150 °C for 5 minutes. In order to keep the polyimide film flat during the whole process, it was attached to a 4 inch Si wafer spin-coated with polydimethylsiloxane (PDMS). We deposited 10 nm Cr and 100 nm Au with electron-beam evaporation. The metal wires and contact pads were patterned with S1818 photoresist and wet etching. A 9 μm thick SU8-2007 was spin-coated and patterned to serve as the encapsulation layer. The dimension of each electrode is 250 μm × 250 μm and the distance between adjacent electrodes is 500 μm
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