Wen Li’s group at Michigan State University recently presented preliminary results on the development of an epidural micro-electrocorticogram (μECoG) array combining microelectrodes and light emitting diodes (LEDs) for optical neural stimulation. This work follows-up on a new line of research aiming at providing μECoG arrays with versatile optical stimulation capabilities (see for example the work of Ledochowitsch et al). The “Opto-μECoG” arrays developped in Wen Li’s group were especially designed to address three major limitations of current designs, in particular the limited cortical area and spatial resolution available for optical stimulation. The key features of these Opto-μECoG arrays are the following:
- Untethered system: integration of surface mounted μ-LED light sources (220 × 270 ×50 μm3, wavelength peak at 460nm, Cree® TR2227TM) on the Opto-μECoG array allows the possibility to achieve a truly untethered system.
- Maximized target cortical area available for optical stimulation: optically transparent indium tin oxide (ITO)  epidural electrodes of the Opto-μECoG array allow maximum exposure of the target cortical area for optical stimulation.
- Maximized spatial resolution of optical stimulation: the embedded light sources, placed on top of the ITO electrodes, were preciously arranged based on a recent study of the optimal spacing of subdural, epidural, and scalp electrodes by Slutzky et al.  to cover the entire cortical area of interest, while the effective area of a single light source are minimized for higher spatial resolution for stimulation.
Epidural placement of the device on the cortex minimizes the potential risk of brain tissue damage. Integrated light sources also allow the possibility to achieve a truly untethered system, which is crucial for chronic behavioral experiment.
Read the original manuscript here.
 K. Kwon, B. Sirowatka, A. Weber, and W. Li, “Opto-μECoG array: transparent ECoG electrode array and integrated LEDs for optogenetics,” IEEE Biomedical Circuits and Systems Conference (BioCAS 2012), Hsinchu, Taiwan, vol., no., pp.164-167, Nov. 28-30, 2012.
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 M. W. Slutzky, L. R. Jordan, T. Krieg, M. Chen, D. J. Mogul, and L. E. Miller, “Optimal spacing of surface electrode arrays for brain–machine interface applications,” Journal of Neural Engineering, vol. 7, no. 2, pp. 026004, Mar. 2010.