Transient Potentials Transmitted by an Artificial Electrochemical Synapse
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TRANSIENT POTENTIALS TRANSMITTED BY AN ARTIFICIAL ELECTROCHEMICAL SYNAPSE
T.Triffet, P.Calvert and T.W.Huntoon, NASA Space Engineering Research Center, University of Arizona, Tucson, AZ 85712, USA.
Abstract Experiments have been made with a simple device consisting of two asymmetrically insulated electrodes separated by a thin electrolytic layer. This device has been found to exhibit a wide variety of transient potentials similar to those transmitted by biological synapses, thus suggesting the possibility of constructing a network of similar devices which simulates the behaviour of a biological neural network. 1. Introduction This paper summarizes some preliminary results of experiments designed to develop a device which may be regarded as an artificial synapse in the same sense that the transistorized electrical connections in all current simulated neural networks may be so regarded. The device is different from these, however, in that its operation depends on its chemical as well as its electrical properties, thereby offering the possibility of incorporating the type of electrochemical synapses so commonly found in real neurobiological networks, and on which their functional characteristics critically depend. The device described in the following section satisfies all of these requirements, and though it is comparable with the ChemFET circuits used for the detection of ions (see Sibbald, Whalley and Covington, 1984; Josowicz and Janata,1986), as well as the "memsistor" device proposed by Widrow (1987), it is simpler and has a very different purpose. Of particular interest is the range of complex responses that can arise from effects such as surface adsorption, impurity poisoning and localized plating of metal. These factors are of especial importance in a device with such a high surface-volume ratio and are expected to be important in the tuning of the device response and the incorporation of a "memory" function. 2. The Artificial Electrochemical Synapse As shown in the schematic diagrams of Figure 1, the device consists typically of a thin copper wire embedded in a block of insulating material, such as an epoxy or acrylic resin, with a plane surface adjacent to a flat copper plate, so that the end of the wire is as close as possible to (within about 10 microns), without actually touching, the plate. A drop of electrolytic fluid is introduced to create a conducting film in whatever space remains between the plane surface of the insulator and the copper plate. A
Mat. Res. Soc. Symp. Proc. Vol. 218. 01991 Materials Research Society
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Figure I.
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potential difference may be established very rapidly across the electrolytic gap by closing a circuit of which the end of the wire and the surface of the plate form opposing electrodes. It will be noticed that the asymmetry of this configuration arises partly from the different (insulating and conducting) materials brought into conjunction, but more essentially from the very different areas of the two electrodes in contact with the electrolyte. The configura
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