Biology subjects

Chapman, I. F.

Publications and source records attributed to Chapman, I. F..

3 recordsLinked to original sources

bioRxiv2026

Aging reshapes odor-evoked dynamics in central olfactory circuits

Olfactory decline is among the earliest signs of aging and predicts later cognitive decline and neurodegenerative disease. Age-related impairments in odor identification and discrimination implicate central olfactory brain regions in both mice and humans, but it remains unclear where in the processing hierarchy aging alters neural function relating to these cognitive and perceptual deficits. To resolve this, we acquired simultaneous Neuropixels recordings from olfactory bulb (OB) and piriform cortex (PCx) in young and old mice during awake, head-fixed odor presentation, allowing us to probe multiple levels of odor response features within each animal. Our recordings revealed a shift toward greater excitation in both regions and reduced inhibitory neuron activity in PCx. Aging also restructured odor-evoked local field potential (LFP) oscillations within and across regions, with strongly elevated beta power and coherence. Population odor representations were less discriminable in OB, but not in PCx. Thus, our results point to reduced discriminability of OB population odor representations as the clearest neural analog of previously reported discrimination deficits. Single-unit, LFP, and population measures did not collapse onto a single axis using dimensionality reduction, indicating that several partly independent processes reshape the dynamics of odor responses in central olfactory circuits with aging. Together, these findings identify central circuit excitation/inhibition (E/I) and oscillatory imbalances that parallel age-related olfactory dysfunction despite largely preserved odor responsivity.

neuroscience↗

bioRxiv2024

Neural coding in gustatory cortex reflects consumption decisions: Evidence from conditioned taste aversion

Taste-responsive neurons in the gustatory cortex (GC) have been shown to encode multiple properties of stimuli, including whether they are palatable or not. Previous studies have suggested that a form of taste-involved learning, conditioned taste aversion (CTA), may alter the cortical representation of taste stimuli in a number of ways. We used miniscopes to image taste responses from a large population of neurons in the gustatory cortex of mice before and after CTA to NaCl, comparing taste responses in control and conditioned mice. Following conditioning, no significant effects on the number of responsive cells, or the magnitude of response to either NaCl or other taste stimuli were found. However, population-level analyses showed that in mice receiving a CTA, the representation of NaCl diverged from other appetitive stimuli in neural space and moved closer to that of aversive quinine. We also tracked extinction of the CTA in a subset of animals and showed that as NaCl became less aversive, the neural pattern reverted to match the behavior. These data suggest that the predominant function of the taste representation in GC is palatability; the neuronal response pattern to stimuli at the population level reflects the decision of the animal to consume or not consume the stimulus, regardless of quality or chemical identity.

neuroscience↗

bioRxiv2024

Experience and behavior modulate piriform cortex odor representation in freely moving mice

In rodents, activity in the piriform cortex (PC) has been shown to reliably encode the identity of olfactory information within single sessions of odor delivery. However, recent evidence from chronic PC recordings found significant unreliability in this ensemble code over longer periods. The causes of this phenomenon, termed representational drift, are still being investigated across multiple sensory systems, but prior work has suggested a role for animal behavior in this observed unreliability of coding. To explore this possibility in PC, we recorded from the same populations of neurons in freely-moving, awake mice using micro-endoscopic calcium imaging as they gained passive experience with a panel of odorants over 5 consecutive days. As in prior studies, PC odor responses within a single session could be used to accurately decode odor identity. However, responses became less consistent across days of experience as odor-evoked response properties of the neurons shifted with experience. During these recordings, within and across sessions, decreases in olfactory investigative behavior correlated with decreased odor-evoked response from PC neurons. Similarly, decreases in odor investigation correlated with a decrease in representational consistency, and trials with greater odor investigation could be used to decode odor identity from PC neurons more accurately over time. Overall, this data supports recent evidence of long-term shifts in the ensembles of PC neurons encoding odor-identity (drift) but supports a role for behavioral modulation of overall PC activity and ensemble response consistency.

neuroscience↗