MANA Researchers Emulate Human Memory with Atomic Inorganic Synapses

A research team at the International Center for Materials Nanoarchitectonics (MANA) have mimicked synaptic activity with the electronic behavior of a nanoscale Ag2S electrode. This is the first time key features in the neuroscience and psychology of memory by a Ag2S synapse have been demonstrated. The research is a breakthrough in artificial neural networks because the complex and interconnected nature of thought processes make neural behavior difficult to reproduce in artificial structures without software programming.

An inorganic synapse showing short-term plasticity and long-term potentiality depending on input-pulse repetition time
An inorganic synapse showing short-term plasticity and long-term potentiality depending on input-pulse repetition time

Researchers at the International Center for Materials Nanoarchitectonics (MANA), Tsukuba, Japan, and the University of California observed a temporary higher-conductance state in the Ag2S system following an incident electric pulse. Repetition of the input pulse over 2-second intervals led to permanently higher conductance. These two responses mimic the short-term plasticity and long-term potentiality in biological synapses.

Their research was published in Nature Materials: 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). In neuromorphic engineering, 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 switch, 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.

Publications and Affiliation
Takeo Ohno1, Tsuyoshi Hasegawa1, Tohru Tsuruoka1, Kazuya Terabe1, James K. Gimzewski1,2,3 and Masakazu Aono1, Short-term plasticity and long-term potentiation mimicked in single inorganic synapses. Nature Materials, 10, 591-595, (2011).

  1. International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
  2. Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), 607 Charles E. Young Drive East, Los Angeles, California 90095, USA
  3. California NanoSystems Institute (CNSI), University of California, Los Angeles (UCLA), 570 Westwood Plaza, Los Angeles, California 90095, USA

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