Months-long tracking of neuronal ensembles spanning multiple brain areas with Ultra-Flexible Tentacle Electrodes

We introduce Ultra-Flexible Tentacle Electrodes (UFTEs), which pack many independent fibers with a cellular-scale footprint and no limitation in recording depth by combining mechanical and chemical tethering for insertion. We demonstrate simultaneous implantation of UFTEs into many brain areas at arbitrary locations and angles, and a 512-channel wireless logger. Immunostaining reveals no detectable chronic tissue damage after several months. Mean spike signal-to-noise ratios (SNRs) are 1.5× higher than state-of-the-art, with maximum mean single-unit SNRs up to 89, and average cortical unit yields of 1.75 per channel. UFTEs track the same neurons across sessions for at least 10 months (longest tested). We simultaneously tracked inter- and intra-areal neuronal ensembles (neurons co-activated within 25 ms) from hippocampus, retrosplenial cortex, and medial prefrontal cortex in freely moving rodents. Ensemble lifetimes were shorter than neuron trackability durations. Two ensemble classes emerged: SWR-tuned ensembles (mostly hippocampal) had the shortest lifetimes, whereas inter-areal hippocampal-cortical ensembles were weakly SWR-tuned and could persist for months, sometimes remaining inactive for weeks before re-emerging.