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[ Development of brain-inspired chemical sensor ]
Sub-project leader : Yoshii
Subproject on taste-bud-like chemical sensor array.
We, physiologists, theorists, and engineers, gather together to develop a new generation chemical sensor inspired by mammalian taste buds, taste organs (Fig. 1). Each taste bud is ~50 m in diameter and height, and consists of ~50 cells. These cells are classified into four cell types, though there are substantial variations within each cell type. Type II cells express taste receptors for sweet, bitter, and umami substances, but they have no synaptic contacts with taste nerves. The only cell type that has the synaptic contacts is type III cells. Recent studies suggest that type II cells transmit their taste information to taste nerves via type III cells (Fig. 2). Such cell-networks may be essential to exercise the excellent ability of taste buds, e.g. in compensating the variations in these cell types. Here we show a software model (Fig. 3) and a hardware model (Fig. 4) for chemical sensor arrays that detect the concentration of chemical substances as the degree of synchronization of bursts. These models are suitable not only in developing new generation chemical sensors, but also in developing brain-like processors.
Fig. 2 Cell-network in taste buds.
Type II cells have taste receptors for sweet, bitter and umami substances, and release ATP in response to these substances. Released ATP stimulates type III cells via paracrine signaling, so that the taste responses of type II cells are transmitted to taste nerves via chemical synapses between type III cells and the taste nerves. See our papers [1, 2, 7] on this issue.
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Fig. 3
Our computational model of a chemical sensor array consists of several tens of leaky integrate-and-fire (LIAF) cells and a pair of non-identical uncoupled bursting cells [3, 4, 8]. The LIAF cell and the bursting cell correspond to the Type II cell and the Type III cell respectively. The LIAF cells show irregular spiking in response to the chemical stimuli. Spikes of the LIAF cells equally converge on the bursting cells. The irregular spikes stochastically entrain bursts in the two bursting cells. The concentration of chemical stimuli is detected as the degree of burst synchronization.
Fig. 4
Schematic diagram of an analog integrated circuit implementing a resonate-and-fire neuron [5] for constituting the stochastic synchronizer part of the chemical sensor array [3, 8] and the layout of the circuit designed by using TSMC 0.35 m process. The assembly of the circuits can act as the stochastic synchronization part on silicon. See details in references [5,6]. Functional implications of physiological cell-networks could improve the performance of the chemical sensor array on silicon under constraints in hardware implementation: a limited number of devices with statistical deviation and their stochastic properties. We also designed and fabricated a prototype chip using a fabrication process originally established by Fuzzy Logic System Institute (FLSI) and founded by Nanotechology Network Japan and Foundation for Advancement of International Science (FAIS) at Kitakyushu Science and Research Park.
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References
[1] K. Eguchi, Y. Ohtubo, K. Yoshii, Functional expression of m3, a muscarinic acetylcholine receptor subtype, in taste bud cells of mouse fungiform papillae, Chem Senses 33, pp.47-55, 2008.
[2] R. Hayato, Y. Ohtubo, K. Yoshii, Functional expression of ionotropic purinergic receptors on mouse taste bud cells, J Physiol 584, pp.473-488, 2007.
[3] J. Igarashi, K. Tateno, K. Nakada, T. Miki, Y. Ohtubo, K. Yoshii, A chemical sensor array inspired by mouse taste buds, Abstracts of BrainIT2007, p.34, 2007.
[4] J. Igarashi, K. Tateno, K. Nakada, T. Miki, Y. Ohtubo, K. Yoshii, Demonstration of a chemical sensor array inspired by mouse taste buds,Abstracts of BrainIT2007, p.70, 2007.
[5] K. Nakada, T. Asai, H. Hayashi, Analog VLSI implementation of resonate-and-fire neuron, Int. J. Neural Systems, vol. 16, no.1, pp. 445-456, 2006.
[6] K. Nakada, K. Tateno, H. Hayashi, K. Yoshii, Functional properties of RFN circuits for bio-inspired chemical sensor array, Abstracts of BrainIT, p.60, 2007.
[7] Y. Ohtubo, T. Suemitsu, S. Shiobara, T. Matsumoto, T. Kumazawa, K. Yoshii, Optical recordings of taste responses from fungiform papillae of mouse in situ. J Physiol 530, pp.287-293, 2001.
[8] K. Tateno, K. Yoshii, Y. Ohtubo, T. Miki, A network model toward a taste bud inspired sensor, International Congress Series, Vol.1301, pp.52-55, 2007.
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