Impact of the entorhinal feed-forward connection to the CA3 on hippocampal coding

Each sub-region of the hippocampus plays a critical computational role in the formation of episodic learning and memory, but studies have yet to show and interpret the individual spiking dynamics of each region and how that information is passed between each subregion. This is in part due to the difficulty in accessing individual communicating axons. Here, we created a novel microfluidic device that facilitates network growth of four separated hippocampal subregions over a micro-electrode array. This device enabled monitoring single axons over two electrodes so direction of spike propagation in interregional communication could be ascertained. In this in vitro hippocampal study, we compared spiking dynamics across two novel four-compartment device architectures: one with four sets of axon tunnels between subregions that excluded the perforant pathway from EC-CA3, and one with five sets of axon tunnels that included the EC-CA3 connection. We found 30-90% faster feed-forward firing rates ..., In vitro hippocampal neuronal network culture in a four-chamber device with four-way and five-way microfluidic interconnections
Microfluidic and culturing methods were previously described in more detail in Vakilna et al. (2021) and Chen et al. (2023). In short, we employed a novel four-chamber device containing microfluidic tunnels for axonal communication between chambers. Each chamber contained dissociated neurons from micro dissections of the entorhinal cortex (EC), dentate gyrus and hilus (DG), CA3, and CA1 including the subiculum from postnatal day 4 Sprague Dawley rat pups under anesthesia as approved by the UC Irvine Institutional Animal Care and Use Committee (IACUC). Brain cells were dissociated and plated at 1,000 cells/mm2 for DG, 330 for CA3, 410 for CA1 (including subiculum), and 330 for EC, in order to reflect in vivo neural densities: EC-DG 1:3, DG-CA3 3:1, CA3-CA1 1:1.25, and CA1-EC 1.25:1 (Braitenberg, 1981). Cells were in 10 μL of NbActiv4 medium (Transnetyx BrainBits..., , # Impact of the entorhinal feed-forward connection to the CA3 on hippocampal coding

[https://doi.org/10.5061/dryad.x0k6djhwb](https://doi.org/10.5061/dryad.x0k6djhwb)

## Description of the data and file structure

The data are stored in MATLAB R2024b (.mat) files within the .zip files. Each zip file contains the data collected for either the four-tunnel MEA architecture experiments or the five-tunnel MEA architecture. The axon and well data are recorded from self-wiring model of the trisynaptic loop and contain subregions from the Entorhinal Cortex (EC), Dentate Gyrus (DG), Cornu Ammonis 3 (CA3), and Cornu Ammonis 1 (CA1) and provided via binary spike trains. The four-tunnel architecture excludes the EC-CA3 connection which is compared to the dynamics of the five-tunnel architecture that does include the EC-CA3 connection. Within either experiment, there are two sub directories for either axon data or well data. The axonal data has been preprocessed so that directions are known from n...,