Within the brain, the interplay between connectivity patterns of neurons and their spatiotemporal dynamics is believed to be intricately linked to the bases of behavior, such as the process of storing, consolidating, and retrieving memory traces. Memory is believed to be stored in the synaptic patterns of anatomical circuitry in the form of increased connectivity densities within subpopulations of neurons. At the same time, memory recall is thought to correspond to activation of discrete areas of the brain corresponding to those memories. Such regional subpopulations can selectively activate during memory recall or retrieval, signifying the process of accessing a single memory or concept. It has been shown previously that recovery of single memory activity patterns is mediated by global neuromodulation signifying transition into different cognitive states such as sleep or awake exploration. We examine how underlying topology can affect memory awake activation and sleep reactivation when such memories share increasing proportions of neurons. The results show that while single memory activation is diminished with increased overlap, pattern separation can be recovered by offsetting excitatory associations between two memories with targeted and heterogeneous inhibitory feedback. Such findings point to the importance of excitatory-to-inhibitory current balance at both the global and local levels in the context of memory retrieval and replay, and highlight the role of network topology in memory management processes.

It has been hypothesized that the brain uses combinatorial as well as temporal coding strategies to represent stimulus properties. The mechanisms and properties of the temporal coding remain undetermined, although it has been postulated that oscillations can mediate formation of this type of code. Here we use a generic model of the vertebrate olfactory bulb to explore the possible role of oscillatory behavior in temporal coding. We show that three mechanisms—synaptic inhibition, slow self-inhibition and input properties—mediate formation of a temporal sequence of simultaneous activations of glomerular modules associated with specific odorants within the oscillatory response. The sequence formed depends on the relative properties of odorant features and thus may mediate discrimination of odorants activating overlapping sets of glomeruli. We suggest that period-doubling transitions may be driven through excitatory feedback from a portion of the olfactory network acting as a coincidence modulator. Furthermore, we hypothesize that the period-doubling transition transforms the temporal code from a roster of odorant components to a signal of odorant identity and facilitates discrimination of individual odorants within mixtures.