Active System Identhesis And Synaptic Homeostasis Hypothesis

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Register to read the introduction… Hippocampal replay is associated with SPW-Rs projecting to the neocortex, reflecting a redistribution of memory traces for long-term storage. Investigations of hippocampal place cells were the first to reveal this phenomenon. In a seminal study, the activity of pairs of hippocampal place cells with overlapping place fields were measured in mice11. Cells that had showed correlated firing during a spatial behavioural task in wake, displayed increased coactivation during SWS, suggesting a ‘replay’ of waking neural activity during sleep. More recently, complex replay was observed in the cortex as well as the hippocampus. High-order replay in the visual cortex and hippocampus during SWS following learning of a complex spatial task in prior wake, were observed as multi-cell spiking patterns ordered into frames12. Frames of activity in the hippocampus were temporally synchronised 50ms behind cortical frames. These results suggest that hippocampal replay is activated by cortical reactivation rather than intrinsic spontaneous activity of the hippocampus. Studies on humans trained to a spatial memory task have also reported hippocampal replay during SWS13. One caveat of these replay studies is that the subjects, particularly animal, were highly overtrained in the spatial tasks in a familiar environment. As a …show more content…
According to this model there is a net synaptic potentiation during wake. This comes at a high energy and space cost, and leads to saturation of learning. Accordingly this potentiation in wake is counterbalanced by a net depression of synaptic weight during sleep. Synaptic homeostasis occurs by a non-Hebbian synaptic downscaling during SWS. Synaptic scaling refers to the global adjustment of all synapses in a neuronal network in response to global changes in network activity30. This form of plasticity is referred to as homeostatic as it reduces the overall input to all neurons, maintaining the relative strength of all synapses. SHY is proposed to have a functional role in memory consolidation as the global downscaling leads to an increase signal to noise ratio. Stronger synapses may even be downscaled less than weaker synapses, as will be discussed in the more recent modified form of SHY31. The molecular, electrophysiological and structural studies that I believe to be the best available evidence for a net potentiation in wake and depotentiation in sleep will be analysed

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