Modulating grid cell scale and intrinsic frequencies via slow high-threshold conductances: A simplified model

Abstract

Grid cells in the medial entorhinal cortex (MEC) have known spatial periodic firing fields which provide a metric for the representation of self location and path planning. The hexagonal tessellation pattern of grid cells scales up progressively along the MEC's layer II dorsal-to-ventral axis. This scaling gradient has been hypothesized to originate either from inter-population synaptic dynamics as postulated by attractor networks, or from projected theta frequencies to different axis levels, as in oscillatory models. Alternatively, cellular dynamics, and specifically slow high-threshold conductances, have been hypothesized to have an effect in the scaling of grid cells. To test the hypothesis these intrinsic hyperpolarization-activated cation currents account for the scale gradient as well as the different oscillatory frequencies observed along the dorsal-to-ventral axis, we have modeled and analyzed data from a population of grid cells simulated with spiking neurons interacting through low-dimensional attractor dynamics. To investigate the causal relationship between oscillatory frequencies and grid scale increase, we analyzed the dominant frequencies of the membrane potential for cells with distinct after-spike dynamics. We observed that intrinsic neuronal membrane properties of simulated cells could induce an increase of grid scale when modulated by after-spike reset values. Differences in the membrane potential oscillatory frequency were observed along the simulated dorsal-to-

Basal forebrain rhythmicity is modulated by the exploration phase of novel environments

“…Moreover, we quantified the decay rate of theta and observed a linear, rather than abrupt, decrease in the oscillatory amplitude as the animal explores a novel environment, which argues in favor of continual assessment of the animal's learning (Fig2-D and E). A piece of accompanying evidence supporting the notion that BF oscillations carry spatially-related information was the observation that gamma oscillatory bursts tend to have a longer duration at later stages of learning (Fig 3-C), a phenomenon previously quantified in the hippocampus of rats during spatial memory tasks (Fernández-Ruiz et al, 2019;Santos-Pata et al, 2019). Furthermore, we evaluated whether phase-amplitude cross-frequency (theta-gamma) coupling had a functional relevance for learning as it is expected from hippocampal oscillations (Fig3-E) (Tort et al, 2009).…”

Human CA1 and subiculum activity forecast stroke chronicity

“…A number of rodent and human studies investigating the functional role of hippocampal subregions support their distinct contributions to cognitive aspects such as spatial representations 31,32 , pattern separation in the dentate gyrus 33 , pattern completion in CA3 34 , temporal ordering in CA1 35 , memory retrieval in subiculum 36,37 and spatial decision-making 38,39 .…”