Auditory corticofugal neurons transmit non-auditory signals to support discriminative learning

Abstract

AbstractLayer 5 pyramidal neurons of sensory cortices project “corticofugal” axons to myriad of sub-cortical targets, thereby broadcasting high-level signals important for perception and learning. Recent studies suggest dendritic Ca2+spikes as key biophysical mechanisms supporting corticofugal neuron function: These long-lasting events drive burst firing, thereby initiating uniquely powerful signals to modulate sub-cortical representations and trigger learning-related plasticity. However, the behavioral relevance of corticofugal dendritic spikes is poorly understood. We shed light on this issue using 2-photon Ca2+ imaging of auditory corticofugal dendrites as mice engage in a sound-discrimination task. Unexpectedly, only a minority of dendritic spikes were triggered by sound. Rather, task-related dendritic activity mostly occurred following sound termination and reflected mice’s instrumental actions, irrespective of reward consumption. Temporally selective silencing of this motor-related activity impaired auditory discrimination learning. Thus, corticofugal systems’ contribution to learning and plasticity may be largely motor, rather than sensory in nature.