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.