Photoreceptors of the vertebrate retina are known to release the neurotransmitter in the dark and decrease the rate of neurotransmitter release during the graded hyperpolarization in response to the light. To transmit such graded signal to the second order neurons, intracellular Ca²⁺ concentration ([Ca²⁺]_i) of the photoreceptor terminal is considered to be regulated with the level of hyperpolarization. The purpose of the present study is to elucidate how [Ca²⁺]_i of the cone photoreceptor terminal is regulated by the Ca²⁺ conductance and the plasma membrane calcium ATPase (PMCA) with the aid of computer simulations. Physiologically realistic models of the Ca²⁺ conductance and the PMCA of the mammalian cone photoreceptor inner segment were reconstructed from the voltage clamp and Ca²⁺ imaging experiments which were carried out on the isolated photoreceptor inner segments in previous studies. The physiological ranges of parameters of the model equations describing the voltage-gated calcium channels were estimated by referring to previous experiments. The parameters of the model equation describing the PMCA were estimated by assuming steady levels of [Ca²⁺]_i. Dynamical change of [Ca²⁺]_i at the terminal region was calculated using the estimated parameters. When the conductance and PMCA are evenly distributed in entire model terminal, [Ca²⁺]_i was reduced from 1-2µM to 30nM in response to a voltage change from -45mV to -55mV which is relevant to the light-induced hyperpolarization to moderate light. The model of physiological mechanisms developed in the present study can be used to elucidate the underlying mechanisms of the light-induced response of the cone photoreceptor terminal in situ.

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An associative memory model is useful not only for application of information science but for brain's model. In this paper, an associative memory model is employed to elucidate the mechanisms of neuronal responses in the inferior-temporal (IT) cortex. The behavior of the model qualitatively coincides with the responses of IT neurons. Furthermore, we propose three physiological experiments and predict the results from our model. If the results obtained by actual physiological experiments coincide with our predicted results, the associative memory model might be the mechanisms producing the responses of the IT neurons.

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連想記憶と携帯電話の間に思いがけない数理的な関連性が発見された．この関連とはどのようなものであるかを中心として，連想記憶の理論がどのように携帯電話に役立つのかを解説する．

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非対称リカレント型神経回路網モデルにおいて，システムパラメータを変化させることによりリミットサイクル型の記憶機能を持たせつつ，それに加えてカオス的ダイナミクスを発現させることができる．その二種類の動的状態間の適応的切り換え制御のもと，不確定な記憶パターンの検索や二次元迷路課題といった具体的な不良設定問題求解に上記カオス的ダイナミクスを応用して機能実験（コンピュータシミュレーション）を行った研究を紹介する．生体機能におけるカオスを含む複雑なダイナミクスの機能的役割に関して，本研究が「似て非なるもの」との限界を意識しつつ「Neuromorphic Engineering」として「単純な制御ルールによる複雑な機能」を発現させることができる場合があることを示す．

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Associative memory in neural-neural network systems has long been described by dynamical systems with discrete attractors. Recent neurophysiological findings of graded persistent activity, however, suggest that memory retrieval in the brain is more likely to be described by dynamical systems with continuous attractors. This paper briefly reviews experimental studies of graded persistent activity and computational studies for modelling its neural mechanisms by continuous attractor dynamics. Furthermore, their implications for associative memory are discussed.

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