Are binary synapses superior to graded weight representations in stochastic attractor networks?

Synaptic plasticity is an underlying mechanism of learning and memory in neural systems, but it is controversial whether synaptic efficacy is modulated in a graded or binary manner. It has been argued that binary synaptic weights would be less susceptible to noise than graded weights, which has impelled some theoretical neuroscientists to shift from the use of graded to binary weights in their models. We compare retrieval performance of models using both binary and graded weight representations through numerical simulations of stochastic attractor networks. We also investigate stochastic attractor models using multiple discrete levels of weight states, and then investigate the optimal threshold for dilution of binary weight representations. Our results show that a binary weight representation is not less susceptible to noise than a graded weight representation in stochastic attractor models, and we find that the load capacities with an increasing number of weight states rapidly reach the load capacity with graded weights. The optimal threshold for dilution of binary weight representations under stochastic conditions occurs when approximately 50% of the smallest weights are set to zero

The role of sleep in emotional processing

Abstract In this chapter, we have reviewed an extensive literature supporting the 4 critical role of sleep for several aspects of emotional processing and regulation. In the first part, we discussed the main behavioral and psychophysiological studies that examined how sleep influences the processes of encoding and consolidation of emotional memory. In addition, we examined how sleep modulates emotion regulation, emotional reactivity, and empathy. Further, we discussed the implication of sleep in fear conditioning memory, threat generalization, and extinction memory. In the second part, we discussed evidence specifically suggesting the implication of REM sleep in the consolidation of emotional memory and in the modulation of emotional reactivity. In particular, we will focus on the specific physiological REM features that contributed to suggest its critical involvement in emotional processing. In the third part, we overviewed the functional neuroimaging studies on the brain mechanisms that underlie the relations between sleep and emotions. Finally, we focused on the most important psychiatric disorders that express abnormalities of sleep and emotional alterations, briefly reviewing our knowledge about the relationships between sleep disturbances and mood in major depression, anxiety disorders, and post-traumatic stress disorder. We showed that sleep helps in the formation of emotional memories at every stage of this process. On the contrary, sleep loss induces deficit in encoding of emotional information, leading to a disruptive interference with emotional memory consolidation. The reviewed literatures clearly suggest that sleep loss significantly influences emotional reactivity. Whether sleep acts to protect, potentiate, or de-potentiate emotional reactivity is, however, still debatable. Future studies will have to elucidate, at the behavioral level, the specific direction of the sleep-dependent emotional modulation. Sleep seems to be crucial also for our ability to correctly process emotional information that allows us to understand the others’ feelings and to be empathic with them, as well as for our ability to encode and consolidate fear conditioning and extinction learning. As far as the role of REM sleep is concerned, it seems to be crucial for the consolidation of emotional memory, while its specific contribution on next-day emotional reactivity is less clear. In fact, REM sleep could act to potentiate or, conversely, de-potentiate the emotional charge associated to a memory along with its consolidation. This topic could be also relevant for its implications in clinical settings. Indeed, further explaining how sleep influences the next-day emotional brain functioning will be crucial to open a new perspective for the understanding and treatment of affective or anxiety disturbances in patients with disturbed sleep