Biology subjects

Harris, J. J.

Publications and source records attributed to Harris, J. J..

4 recordsLinked to original sources

bioRxiv2026

Decomposing representational drift across wake and sleep

Neural representations evolve over time, yet the relative contributions of online experience and offline states such as sleep remain unclear. Here, we recorded single-unit activity in the olfactory cortex of mice across cycles of awake odour exposure and sleep, and developed a low-rank decoder to track representational drift. We identified four orthogonal drift modes operating on distinct timescales, revealing that sleep and wake drive qualitatively different transformations, which indicates that offline reorganisation is not a simple continuation of online learning. Rather, sleep initiates an about-turn in the overall drift trajectory, which is uniquely characterised by a combination of decorrelation and rotation of odour representations. We also provide the first evidence for olfactory replay, occurring at ~2.5x temporal compression and associated with locally generated piriform cortex sharp waves. Together, these findings demonstrate that representational drift comprises state-dependent components, and reveal distinct contributions of wake and sleep to sensory representational change.

neuroscience↗

bioRxiv2025

Mice discriminate odour source distance via sub-sniff temporal features of odour plumes

Rodents rely on olfaction to navigate complex environments, particularly where visual cues are limited. Yet how they estimate the distance to an odour source remains unclear. The spatiotemporal dynamics of natural odour plumes, shaped by airflow turbulence, offer valuable cues for locating odour sources. Here, we show that mice can discriminate odour sources placed at different distances by extracting information from the sub-sniff temporal structure of naturalistic odour plumes. Using a wind tunnel and an olfactory virtual reality system, we generated dynamic plumes and demonstrated, through high-throughput automated behaviour, that mice distinguish near from far sources based on odour fluctuations operating faster than their respiratory cycle. Two-photon calcium imaging of olfactory bulb projection neurons revealed that distance-dependent responses are present in a small subset of mitral and tufted cells, and that population activity encodes source distance. Critically, neural responses correlated more strongly with high-frequency plume features than with mean odour concentration. Our results identify a neural basis for distance estimation from odour dynamics and highlight the importance of rapid temporal processing in mammalian olfaction.

neuroscience↗

bioRxiv2023

Wireless monitoring of respiration with EEG reveals relationships between respiration, behaviour and brain activity in freely moving mice

Active sampling in the olfactory domain is an important aspect of mouse behaviour. Numerous methods are being used to measure active sampling behaviour, yet reliable observation of respiration in untethered, freely moving animals is challenging. So far, methods for measuring this have largely been restricted to head-fixed sniff monitoring, which makes it difficult to understand how sniff changes are related to natural mouse behaviour. Here, we implant a telemetry-based pressure sensor into the right jugular vein, which allows respiration to be measured via wireless thoracic pressure sensing in awake and freely moving, untethered mice. After verifying this technique against standard head-fixed respiration measurements, we investigated respiration patterns across a range of experiments in freely moving animals. Respiration frequency increased as mice voluntarily explored novel environmental cues. Combining wireless respiration measurements with EEG/EMG recording, we then used an evolving partial coherence analysis to uncover the direct relationships between respiration and brain activity in different frequency bands over the same exploration period. Finally, we examined respiration patterns across different vigilance states, revealing changes in passive respiration frequency across wakefulness, deep (NREM) sleep and dreaming (REM) sleep, and odour-triggered respiration increases in the absence of brain activity changes during NREM sleep. As it can be combined with behavioural assays and brain recordings, we anticipate that wireless respiration monitoring will be a valuable tool to increase our understanding of how mice use olfaction to process and interact with the environment around them.

neuroscience↗

bioRxiv2022

A role for MCH neuron firing in hippocampal plasticity and learning

It has been revealed that melanin-concentrating hormone (MCH) neurons in the hypothalamus can influence learning (Liu et al., 2022) and memory formation (Kosse & Burdakov, 2019), but the cellular mechanisms by which they perform this function are not understood. Here, we examine the role of MCH neural input to the hippocampus, and show in vitro that optogenetically increasing MCH axon activity facilitates hippocampal plasticity by lowering the threshold for synaptic potentiation. In vivo, we find that MCH neurons are naturally active in response to reinforcing cues during a spatial learning task, and that this activity is correlated with the speed of learning. Together, our results align with increasing evidence that MCH neurons play an on-line regulatory role in learning, and reveal that this could be achieved through modulation of synaptic plasticity in the hippocampus.

neuroscience↗