Conditional Bistability, a Generic Cellular Mnemonic Mechanism for Robust and Flexible Working Memory Computations.

Persistent neural activity, the substrate of working memory, is thought to emerge from synaptic reverberation within recurrent networks. However, reverberation models do not robustly explain the fundamental dynamics of persistent activity, including high-spiking irregularity, large intertrial variability, and state transitions. While cellular bistability may contribute to persistent activity, its rigidity appears incompatible with persistent activity labile characteristics. Here, we unravel in a cellular model a form of spike-mediated conditional bistability that is robust and generic. and provides a rich repertoire of mnemonic computations. Under asynchronous synaptic inputs of the awakened state, conditional bistability generates spiking/bursting episodes, accounting for the irregularity, variability, and state transitions characterizing persistent activity. This mechanism has likely been overlooked because of the subthreshold input it requires, and we predict how to assess it experimentally. Our results suggest a reexamination of the role of intrinsic properties in the collective network dynamics responsible for flexible working memory.SIGNIFICANCE STATEMENT This study unravels a novel form of intrinsic neuronal property: conditional bistability. We show that, thanks to its conditional character, conditional bistability favors the emergence of flexible and robust forms of persistent activity in PFC neural networks, in opposition to previously studied classical forms of absolute bistability. Specifically, we demonstrate for the first time that conditional bistability (1) is a generic biophysical spike-dependent mechanism of layer V pyramidal neurons in the PFC and that (2) it accounts for essential neurodynamical features for the organization and flexibility of PFC persistent activity (the large irregularity and intertrial variability of the discharge and its organization under discrete stable states), which remain unexplained in a robust fashion by current models.

High-performance silver-dielectric interference filters for RGBIR imaging.

New architectures of interference silver-dielectric multilayer filters inspired from induced transmission designs are investigated with the prospect of high-performance red-green-blue (RGB) complementary metal oxide semiconductor imaging. The optimized designs provide combined colorimetric, signal-to-noise ratio and sensitivity performances similar to the traditional organic color filters, but without the equirement of an external infrared (IR)-cut filter, which enables the integration of additional channels such as white or IR, in addition to RGB. Due to the sub-micrometer thickness of the stacks, this is a unique solution for fully integrated, high-performance multispectral filters patterned in very small pixels. The concept is demonstrated by a wafer-scale prototype with RGBIR filters patterned down to 1.4 µm adjacent pixels with up to 80% transmission.

Nicotinic receptors in the ventral tegmental area promote uncertainty-seeking.

Cholinergic neurotransmission affects decision-making, notably through the modulation of perceptual processing in the cortex. In addition, acetylcholine acts on value-based decisions through as yet unknown mechanisms. We found that nicotinic acetylcholine receptors (nAChRs) expressed in the ventral tegmental area (VTA) are involved in the translation of expected uncertainty into motivational value. We developed a multi-armed bandit task for mice with three locations, each associated with a different reward probability. We found that mice lacking the nAChR ß2 subunit showed less uncertainty-seeking than their wild-type counterparts. Using model-based analysis, we found that reward uncertainty motivated wild-type mice, but not mice lacking the nAChR ß2 subunit. Selective re-expression of the ß2 subunit in the VTA was sufficient to restore spontaneous bursting activity in dopamine neurons and uncertainty-seeking. Our results reveal an unanticipated role for subcortical nAChRs in motivation induced by expected uncertainty and provide a parsimonious account for a wealth of behaviors related to nAChRs in the VTA expressing the ß2 subunit.