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Light addressing is an emerging technique to optically address a virtual electrode on a photoconductive substrate. A thinner photoconductive layer of a light-addressable planar electrode can improve the spatial resolution of the light-addressed electrode. Voltage application to the electrode, however, causes a strong electric field across the thin photoconductive layer with a significant avalanche effect, which induces an undesired increase of dark current. In order to overcome this problem, we investigated how photoconductive-layer thickness and passivation-layer conductivity affect voltage-application-induced bright and dark charge densities. Suppression of the dark charge density with a thick photoconductive layer and a low-conductive passivation layer is found to be a key factor for optimization of the light-addressable electrode. With this design strategy, we developed a novel light-addressable electrode using titanium dioxide as a photoconductor. To suppress the avalanche effect, the thickness of the titanium-dioxide layer was designed to be 1.5 μm. The fabricated electrode turned out to have sufficient photoelectric properties: the bright charge density reached 70 μC/cm and the bright-to-dark charge density ratio was greater than 10, which allows stimulation to cultured dissociated neurons. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 94(1): 61-68, 2011; Published online in Wiley Online Library (). DOI 10.1002/ecj.10241 [ABSTRACT FROM AUTHOR]

Information transfer among neuronal populations has a directional bias. Some past studies demonstrated that microstructure could bias the direction of information transfer at a cellular level. However, the transfer at a population level has hardly been controlled to date. In order to control the information transfer, we attempt to bias the direction of neurite outgrowth of cultured neurons using a three-dimensional asymmetric microstructure. The proposed microstructure is an embossed barrier with a right-triangle cross section, namely, an ascending slope and vertical wall. Because of the asymmetricity, the neurite growth rate from the wall-side to the slope-side is expected to be lower than that of the slope-to-wall. We fabricated the microstructure on a polystyrene substrate by hot pressing, simultaneously embedding line electrodes for probing stimulation. To confirm the impact of the microstructure on neurite outgrowth, and thus the signal transfer direction between neuronal populations separated by the structure, we stimulated cultured neurons on both sides of the structure. There was a difference in neuronal responses to wall-side stimulation and slope-side stimulation, demonstrating the directional characteristic of information transfer. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(12): 17-25, 2010; Published online in Wiley Online Library (). DOI 10.1002/ecj.10240 [ABSTRACT FROM AUTHOR]

This paper proposes a penetration-type tungsten microelectrode array on a flexible silicone rubber substrate for neural recording from a desired cortical layer. Our evaluation experiments confirmed that the flexible substrate keeps the penetration depth of each electrode constant and allows simultaneous multipoint recording of spike potentials from a desired neocortical layer. Penetration of the stiff and flexible arrays into agarose specimens with a curvature comparable to that of the rat brain, revealed that the electrodes at the edge of the stiff array had up to 150 μm error in penetration depth, while the penetration depth of the flexible array was approximately constant across the electrodes (ANOVA, p=0.835). Electrophysiological experiments in the rat auditory cortex demonstrated that simultaneous multipoint recording of the acoustically evoked spike potentials was feasible with the flexible array. A series of penetration trials and characteristic frequency estimations successfully identified the primary auditory cortex by assuring a gradual increase in the characteristic frequencies from caudal to rostral. This result suggests that the proposed electrode is suitable for acute experiments requiring repeated penetration and precision positioning of penetration sites. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(7): 21-28, 2009; Published online in Wiley InterScience (). DOI 10.1002/ecj.10060 [ABSTRACT FROM AUTHOR]