Functional brain mapping using optical imaging of intrinsic signals and simultaneous high-resolution cortical electrophysiology with a flexible, transparent microelectrode array

Intrinsic optical signal imaging (IOSI) records tiny changes in optical reflection of the exposed cortical surface due to neuronal activation related local hemodynamic changes. Cortical electrophysiology performed in the very same visual cortical area may provide additional insight into the connectivity between functional domains. Our aim is to investigate the simultaneous use of IOSI and mu ECoG (micro-electrocorticography) techniques by introducing a transparent polymer based subdural microelectrode array into the optical recording chamber used for in vivo functional mapping experiments in anaesthetized cats. To demonstrate the feasibility of the combined optical-electrical recording, we have run several stimulus protocols and measured the evoked optical and electrical responses of the primary visual cortex in a synchronized manner. Optical quality of IOSI signals (609 nm) was also evaluated without the ECoG microelectrode as a reference. During the visual stimulus, local field potential on a 32-channel of the ECoG was simultaneously recorded and evaluated. Specific power density distribution was detected in wide band frequency range, and the distribution of a unique 80 Hz oscillation in gamma range occurring only as a response to stimuli was also found. This is the first demonstration of micro-electrocorticography using PI/ITO/PI based microelectrode arrays in combination with in vivo IOSI.