Basic neuroscienceA transparent epidural electrode array for use in conjunction with optical imaging

- We present a method to produce an exceedingly transparent electrode array.
- The electrode possesses epidural recording/stimulation capabilities.
- Optical signals from the cortex can be detected using the electrode array.
- Sensory-evoked LFP recordings were simultaneously performed with optical imaging.
- Neural activity was visualized following anodal/cathodal direct cortical stimulation.

BackgroundCombining optical imaging and direct cortical stimulation can be a powerful technique for high-resolution functional mapping of the cortex. However, stimulating electrodes often obstruct the field of view, resulting in a lack of functional images behind the electrodes.New methodTo overcome this problem, we developed a transparent electrode array with 16-contact grids for epidural cortical stimulation. Using a commercially available indium tin oxide (ITO)-coated polyethylene terephthalate (PET) sheet, the electrode array was fabricated using a photolithography process. Because a complete circuit pattern, including the electrode contact itself, was formed in the transparent metal ITO layer, our electrode array was completely transparent and therefore could be used with optical imaging.ResultsCortical stimulation was performed using the transparent electrode array. Evoked neural activity was successfully monitored through the array using a voltage-sensitive dye and optical imaging. The newly developed electrode array made it possible to detect optical signals from directly below the stimulating electrode. The electrode array could also be used for epidural recording of somatosensory evoked potentials.Comparison with existing methodsA variety of surface electrodes for cortical recording and stimulation exist. However, this study aimed to make electrodes as transparent as possible. We provided a simple and low-cost fabrication process for producing the transparent electrode arrays.ConclusionsOur transparent epidural electrode can be used for both stimulation and recordings without interfering with the detection of optical signals from the underlying cortex.