  Orchestration of diverse synaptic plasticity mechanisms across different
timescales produces complex cognitive processes. To achieve comparable
cognitive complexity in memristive neuromorphic systems, devices that are
capable to emulate short- and long-term plasticity (STP and LTP, respectively)
concomitantly are essential. However, this fundamental bionic trait has not
been reported in any existing memristors where STP and LTP can only be induced
selectively because of the inability to be decoupled using different loci and
mechanisms. In this work, we report the first demonstration of truly
concomitant STP and LTP in a three-terminal memristor that uses independent
physical phenomena to represent each form of plasticity. The emerging layered
material Bi2O2Se is used in memristor for the first time, opening up the
prospects for ultra-thin, high-speed and low-power neuromorphic devices. The
concerted action of STP and LTP in our memristor allows full-range modulation
of the transient synaptic efficacy, from depression to facilitation, by
stimulus frequency or intensity, providing a versatile device platform for
neuromorphic function implementation. A recurrent neural circuitry model is
developed to simulate the intricate "sleep-wake cycle autoregulation" process,
in which the concomitance of STP and LTP is posited as a key factor in enabling
this neural homeostasis. This work sheds new light on the highly sophisticated
computational capabilities of memristors and their prospects for realization of
advanced neuromorphic functions.
