Hierarchical organization of the forebrain cholinergic system in rats

The basal forebrain (BF) cholinergic system (BFCS) participates in functions that are global across the brain, such as sleep-wake cycles, but also participates in capacities that are more behaviorally and anatomically specific, including sensory perception. However, how it orchestrates all the diverse local and global functions remains to be understood. To uncover the underlying organization principles, we combined data from rat brains by tracing projections from the BF to cortical areas and analyzed spatial-numerical relations of neurons to their cortical targets. The combined dataset revealed algorithmically identified and hierarchically organized three principal networks: somatosensory-motor, auditory, and visual, as defined by the sensory modality most predominant within them. These clusters of cholinergic neurons could enable the BFCS to coordinate spatially selective signaling, including parallel modulation of multiple functionally interconnected yet diverse groups of cortical areas. This previously unseen blueprint of the hierarchy of cholinergic clusters is ready for functional testing. The data file (cellpopulations.json) contains cell positions of cholinergic neurons in the Basal Forebrain projecting to different cortical areas. Each cell record is labeled by the name of the cortical area where it projects and by the brain identifier of the individual experiment. The record also contains the image identifier image position and image scale of the section where the neuron in question belongs.