Optimal storage and recall with biologically plausible synapses

Synaptic plasticity is widely accepted to underlie learning and memory. Yet, models of associative networks with biologically plausible synapses fail to match brain performance: memories stored in such networks are quickly overwritten by ongoing plasticity (Amit & Fusi 1996, Fusi et al 2007). Metaplasticity - the process by which neural activity changes the ability of synapses to exhibit further plasticity - is believed to increase memory capacity (Fusi et al 2005). However, it remains unclear if neurons can make use of this additional information during recall. In particular, previous attempts at reading out information in metaplastic synapses using heuristic recall dynamics led to rather poor performance (Huang & Amit 2010).

Here, we developed a theoretical framework for storage and recall with finite-state synapses that allowed us to find neural and synaptic dynamics that maximize the efficiency of autoassociative recall. 
Since information storage by synaptic plasticity is lossy, we formulated the problem of recalling a previously stored pattern from a noisy cue as probabilistic inference (Lengyel et al 2005) and derived neural dynamics efficiently implementing such inferences. Our approach is general and can be applied to any synaptic plasticity model which involves stochastic transitions between a finite set of states.
We show how synaptic plasticity rules need to be matched to the statistics of stored patterns, and how recall dynamics need to be matched both to input statistics and to the plasticity rule itself in order to achieve optimal performance. In particular, for binary synapses with metastates we demonstrate for the first time that memories can be efficiently read out with biologically plausible network dynamics that we derive directly from the synaptic metaplasticity rule with virtually no free parameters

Translating alienation – between escapism and adventure

The poems translated have been selected from Vasile Baghiu’s debut poetry collection The taste of alienation. Published in 1994, the collection represents the genesis of Baghiu’s story of poetic chimerism that spans three decades and eight volumes of poems. But the first chimeric ideas materialised, quietly, six years before The taste of alienation saw the light of day, at the height of the totalitarian regime in his native Romania. At the time, the poet was working as a nurse in a tuberculosis sanatorium, consumed by a sense of isolation in the depths of which he had a life-altering, liberating epiphany that shaped his identity and his understanding of the world. He realised that he could be someone else, that he could escape the personal, geographical and intellectual constraints imposed by the regime, and could virtually live a parallel life. And so poetic chimerism was born, as a means of evading ‘les maux de la société’, as a form of personal freedom made possible through imagination and the re-creation, in writing, of imaginary travels through space and time.