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Short-term plasticity and long-term potentiation mimicked in single inorganic synapses


Memory is believed to occur in the human brain as a result of two types of synaptic plasticity: short-term plasticity (STP) and long-term potentiation (LTP; refs 1, 2, 3, 4). In neuromorphic engineering5,6, emulation of known neural behaviour has proven to be difficult to implement in software because of the highly complex interconnected nature of thought processes. Here we report the discovery of a Ag2S inorganic synapse, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time. The structure known as an atomic switch7,8, operating at critical voltages, stores information as STP with a spontaneous decay of conductance level in response to intermittent input stimuli, whereas frequent stimulation results in a transition to LTP. The Ag2S inorganic synapse has interesting characteristics with analogies to an individual biological synapse, and achieves dynamic memorization in a single device without the need of external preprogramming. A psychological model related to the process of memorizing and forgetting is also demonstrated using the inorganic synapses. Our Ag2S element indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.

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Figure 1: Inorganic synapse showing STP and LTP, depending on input-pulse repetition time.
Figure 2: LTP formation depending on input-pulse repetition time.
Figure 3: The multistore model and the human-memory forgetting curve.
Figure 4: Image memorizing into an inorganic synapse array.

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This research was supported in part by a MEXT grant (Key-Technology Research Project ‘Atomic Switch Programmed Device’) and by a JST grant (Strategic Japanese–German Cooperative Program). We thank A. Nayak for help with measurement of the retention time.

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Authors and Affiliations



T.O. and T.H. designed the experiments. T.O., T.H. and J.K.G. wrote the paper. T.O. also carried out the experiments and analysed the data. T.T. and K.T. contributed to the materials and analysis. All authors discussed the results and commented on the manuscript. T.H. and M.A. directed the projects.

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Correspondence to Takeo Ohno or Tsuyoshi Hasegawa.

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The authors declare no competing financial interests.

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Ohno, T., Hasegawa, T., Tsuruoka, T. et al. Short-term plasticity and long-term potentiation mimicked in single inorganic synapses. Nature Mater 10, 591–595 (2011).

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