A parallel channel of state-dependent sensory signaling from the cholinergic basal forebrain to the auditory cortex
Cholinergic basal forebrain (CBF) signaling exhibits multiple timescales of activity with classic, slow signals related to brain and behavioral states and faster, phasic signals reflecting behavioral events, including movement and reinforcement. Recent evidence suggests that the CBF may also exhibit fast, sensory-evoked responses. It remains unknown, however, whether such sensory signals target the sensory cortex and how they relate to local functional topography. Moreover, the extent to which fast and slow CBF activity interact has been largely unexplored. Here, we used simultaneous two-channel, two-photon imaging of CBF axons and auditory cortical (AC) neurons to reveal that CBF axons project a robust, non-habituating, and stimulus-specific sensory signal to the AC. Individual axon segments exhibited heterogeneous but stable tuning to auditory stimuli allowing stimulus identity to be decoded from the population. However, CBF axons displayed no tonotopy and their frequency tuning was uncoupled from that of nearby cortical neurons. Chemogenetic suppression revealed the auditory thalamus as a principal source of auditory information to the CBF. Finally, slow fluctuations in cholinergic activity modulated the fast, sensory-evoked signals in the same axons, suggesting that a multiplexed combination of fast and slow signals is projected from the CBF to the AC. Taken together, our work demonstrates a novel, non-canonical function of the CBF as a parallel channel of state-dependent sensory signaling to the sensory cortex that provides repeated representations of a broad range of sound stimuli at all points on the tonotopic map.