Hippocampal ensembles represent sequential relationships among an extended sequence of nonspatial events

The hippocampus is critical to the temporal organization of our experiences. Although this fundamental capacity is conserved across modalities and species, its underlying neuronal mechanisms remain unclear. Here we recorded hippocampal activity as rats remembered an extended sequence of nonspatial events and, using novel statistical methods, uncovered new forms of sequential organization in ensemble activity important for order memory judgments. Specifically, we discovered that hippocampal ensembles provide significant temporal coding throughout nonspatial event sequences, differentiate distinct types of task-critical information sequentially within events, exhibit theta-associated replay of the sequential relationships among events, and can represent past, present and future events within individual theta cycles. These findings suggest a fundamental function of the hippocampal network is to encode, preserve, and predict the sequential order of experiences., Recording device and surgery
Each chronically implanted custom microdrive contained 20 independently drivable tetrodes. Each tetrode consisted of four twisted nichrome wire (13 µm in diameter; California Fine Wire) and gold-plated to achieve final tip impedance of ~250 kΩ (measured at 1 kHz). Voltage signals recorded from the tetrode tips were referenced to a ground screw positioned over the cerebellum, and filtered for single-unit activity (154 Hz to 8.8 kHz). The neural signals were then amplified (10,000–32,000X), digitized (40 kHz) and recorded to disk with the data acquisition system (MAP, Plexon). The microdrive was implanted over the left hippocampus, centered on coordinates: -4.0 mm AP, 3.5 mm ML. 
Unit preprocessing and spike sorting
Action potentials from individual neurons were manually isolated offline using a combination of standard waveform features across the four channels of each tetrode (Offline Sorter, Plexon). Proper isolation was verified using interspike interval di..., Please see the included README file., # Hippocampal ensembles represent sequential relationships among an extended sequence of nonspatial events

Shahbaba et al., 2021 Data repository

Readme drafted on October XX, 2021

## Contents

Project summary
Contact information
Dataset Citation
References using this data
Data collection methods and behavior
Description of files
Associated code
Directory Manifest

## 1. Project summary

The hippocampus is critical to the temporal organization of our experiences. Although this fundamental capacity is conserved across modalities and species, its underlying neuronal mechanisms remain unclear. Our work and others suggest a fundamental function of the hippocampal network is to encode, preserve, and predict the sequential order of experiences.

Here, this dataset contains tetrode extracellular recordings from hippocampus (local field potentials and sorted unit spikes) from five male Long–Evans rats. These recordings were performed using a custom electrode microdrive array, positioned alo...