A Transparent Penetrating Microelectrode Array for in-vitro Hippocampus Recording

A novel penetrating microelectrode array was designed and fabricated for the purpose of recording activity in the hippocampus of mice. The array allows two dimensional recording of 64 simultaneous sites of the hippocampus, in vitro. Traditional surface electrode arrays, although easy to fabricate, do not penetrate to the active tissue of hippocampus slices and thus theoretically have a lower signal/noise ratio and lower selectivity than a penetrating array. Furthermore, the structure of the hippocampus slice preparation results in dead tissue in closest proximity to these traditional electrodes and the cell bodies of the CA1 region are obscured by them, degrading activity-based optical imaging techniques as well. An array of 64 electrode posts was fabricated in silicon and bonded to a clear glass substrate. The impedance of the electrodes was measured to be approximately 1.5M Ohms + -500Ohms. The signal to noise ratio was measured and found to be 19.4 +/-3 dB compared to 3.9 +/-0.8 dB S/N for signals obtained with voltage sensitive dye RH414. These data suggest that the penetrating electrode array is superior to that of the voltage sensitive dye technique for two-dimensional recording.