Glomerulus-specific inhomogeneity of the basal activity map in the olfactory bulb supports olfactory-driven behavior

Glomeruli are signal-processing units of the olfactory bulb (OB), playing a key role in many OB computations, including contrast enhancement, gain control, and odorant-selective habituation. In awake mice, we uncover an extremely stable inhomogeneous map of basal glomerulus-specific activity as a background against which olfactory signal processing is performed. This activity is strongly driven by (i) centrifugal cholinergic projections, (ii) endogenous, and (iii) airflow-evoked spiking of olfactory sensory neurons and, to a small extent, (iv) by the odor environment. Importantly, early olfactory impairment in a mouse model of Alzheimer’s disease is parallelled by the loss of glomerular map inhomogeneity and diminished cholinergic innervation. These results reveal an important layer in the signal-processing network of the OB, likely acting by increasing the variance in and dynamic range of the system via glomerulus-specific functional inhomogeneity.