Realising Bio-Synapse Analogous Paired-Pulse Facilitation (PPF) and Release Inactivation (RI) and Emulating "Tip of the Tongue" Experience Through Conductance and Retention Dynamics in Ag Nano-Labyrinth-Based Neuromorphic Device

Abstract

In bio-neural networks, pairing of consecutive action potentials based on the time interval in between, known as paired-pulse facilitation (PPF), is crucial in enhancing synaptic strength and duration. However, at lower time intervals, release inactivation (RI) may set in diminishing the effect of pairing of potentials. While the neuromorphic version of PPF is extensively studied in the literature, aspects related to RI are largely ignored. This study presents a novel two-terminal resistive device utilizing a dewetting-engineered Ag labyrinth structure, designed to emulate the PPF and RI observed in biological synapses. The pulse pairing effect is observed not only based on conductance (G) but also its retention time (tr), with PPF(G) reaching a maximum of ≈2.65 and PPF(tr) ≈12.6. Furthermore, a unique second-order PPF effect is observed when a time interval larger than the first retention is employed; in instances where the retention ended right before the second pulse within a very small interval, pairing effects can still be seen, akin to the “tip of the tongue” experience in humans. Utilizing such inherent volatility of the device is particularly significant for dynamical neural network-based reservoir computing (RC).