Westeinde, E. A. | Search bioRxiv

bioRxiv2021

Parallel pathways for rapid odor processing in lateral entorhinal cortex: Rate and temporal coding by layer 2 subcircuits

Olfactory information is encoded in lateral entorhinal cortex (LEC) by two classes of layer 2 (L2) principal neurons: fan and pyramidal cells. However, the functional properties of L2 neurons are unclear. Here, we show in awake mice that L2 cells respond rapidly to odors during single sniffs and that LEC is essential for discrimination of odor identity and intensity. Population analyses of L2 ensembles reveals that while rate coding distinguishes odor identity, firing rates are weakly concentration-dependent and changes in spike timing represent odor intensity. L2 principal cells differ in afferent olfactory input and connectivity with local inhibitory circuits and the relative timing of pyramidal and fan cell spikes underlies odor intensity coding. Downstream, intensity is encoded purely by spike timing in hippocampal CA1. Together, these results reveal the unique processing of odor information by parallel LEC subcircuits and highlight the importance of temporal coding in higher olfactory areas.

neuroscience↗

bioRxiv2020

Transforming representations of movement from body- to world-centric space

When an animal moves through the world, its brain receives a stream of information about the bodys translational movement. These incoming movement signals, relayed from sensory organs or as copies of motor commands, are referenced relative to the body. Ultimately, such body-centric movement signals must be transformed into world-centric coordinates for navigation1. Here we show that this computation occurs in the fan-shaped body in the Drosophila brain. We identify two cell types in the fan-shaped body, PFNd and PFNv2,3, that conjunctively encode translational velocity signals and heading signals in walking flies. Specifically, PFNd and PFNv neurons form a Cartesian representation of body-centric translational velocity - acquired from premotor brain regions4,5 - that is layered onto a world-centric heading representation inherited from upstream compass neurons6-8. Then, we demonstrate that the next network layer, comprising h{Delta}B neurons, is wired so as to transform the representation of translational velocity from body-centric to world-centric coordinates. We show that this transformation is predicted by a computational model derived directly from electron microscopy connectomic data9. The model illustrates the key role of a specific network motif, whereby the PFN neurons that synapse onto the same h{Delta}B neuron have heading-tuning differences that offset the differences in their preferred body-centric directions of movement. By integrating a world-centric representation of travel velocity over time, it should be possible for the brain to form a working memory of the path traveled through the environment10-12.

neuroscience↗