Fabrication and Investigation of Ferroelectric Memristors with Various Synaptic Plasticities

In the Post-Moore Era, the neuromorphic computing has been mainly focused on breaking the von Neumann bottlenecks. Memristor has been proposed as a key part for the neuromorphic computing architectures, which can be used to emulate the synaptic plasticities of human brain. Ferroelectric memristor is a breakthrough for memristive devices on account of its reliable-nonvolatile storage, low-write/read latency, and tunable-conductive states. However, among the reported ferroelectric memristors, the mechanisms of resistive-switching are still under debate. In addition, the research of emulation of the brain synapses using ferroelectric memristors needs to be further investigated. Herein, the Cu/PbZr0.52Ti0.48O3 (PZT)/Pt ferroelectric memristors have been fabricated. The devices are able to realize the transformation from threshold switching behaviors to resistive switching behaviors. The synaptic plasticities, including excitatory post-synaptic current (EPSC), paired-pulse facilitation (PPF), paired-pulse depression (PPD), and spike time-dependent plasticity (STDP) have been mimicked by the PZT devices. Furthermore, the mechanisms of PZT devices based on the interface barrier and conductive filament models have been investigated by first-principles calculation. This work may contribute to the applications of ferroelectric memristors in neuromorphic computing systems.

Direct Observation Of Vesicle Transport On The Synaptic Ribbon Provides Evidence That Vesicles Are Mobilized And Prepared Rapidly For Release

SUMMARYSynaptic ribbons are thought to provide vesicles for continuous synaptic transmission in some retinal non-spiking neurons, yet recent studies indicate that genetic removal of the ribbon has little effect on vesicle release kinetics. To investigate vesicle replenishment at synaptic ribbons, we imaged synaptic vesicles and ribbons in retinal bipolar cells with TIRF microscopy during stimulation with trains of 30-ms depolarizations. Analysis of vesicles released by the stimuli revealed that the vast majority of releasable vesicles reside within 300 nm of the ribbon center. A single 30-ms step to 0 mV was sufficient to deplete the most membrane-proximal vesicle pool, while triggering rapid stepwise movements of distal vesicles along the ribbon and toward the plasma membrane.Replenishment only becomes rate-limiting for recovery from paired-pulse depression for interstimulus intervals shorter than 250 ms. For longer interstimulus intervals, vesicle movement down the ribbon is fast enough to replenish released vesicles, but newly arrived vesicles are not release-ready. Notably, vesicle re-supply is 40-to 50-fold faster than previously measured in non-ribbon conventional synapses, whereas vesicle maturation rate is comparable. Moreover, in contrast to conventional synapses, vesicles docked at the base of the ribbon release with high fidelity. Lastly, our data show that with multiple stimuli, the delay in vesicle departure increases. Our results support a role for ribbons in the rapid supply and efficient preparation of vesicles for release, provide direct measurements of vesicle movement down the synaptic ribbon and suggest that multiple factors contribute to paired-pulse depression.

Properties of the primary somatosensory cortex projection to the primary motor cortex in the mouse

The primary somatosensory (S1) and primary motor (M1) cortices are reciprocally connected, and their interaction has long been hypothesized to contribute to coordinated motor output. Very little is known, however, about the nature and synaptic properties of the S1 input to M1. Here we wanted to take advantage of a previously developed sensorimotor slice preparation that preserves much of the S1-to-M1 connectivity (Rocco MM, Brumberg JC. J Neurosci Methods 162: 139–147, 2007), as well as available optogenetic methodologies, in order to investigate the synaptic profile of this projection. Our data show that S1 input to pyramidal cells of M1 is highly homogeneous, possesses many features of a “driver” pathway, such as paired-pulse depression and lack of metabotropic glutamate receptor activation, and is mediated through axons that terminate in both small and large synaptic boutons. Our data suggest that S1 provides M1 with afferents that possess synaptic and anatomical characteristics ideal for the delivery of strong inputs that can “drive” postsynaptic M1 cells, thereby potentially affecting their output.