Rapid rebalancing of co-tuned ensemble activity in the auditory cortex

Sensory information is represented by small varying neuronal ensembles in sensory cortices. In the auditory cortex (AC), repeated presentations of the same sound activate differing ensembles, indicating high trial-by-trial variability in activity even though the sounds activate the same percept. Efficient processing of complex acoustic signals requires that these sparsely distributed neuronal ensembles actively interact in order to provide a constant percept. Thus, the differing ensembles might interact to process the incoming sound inputs. Here, we probe interactions within and across ensembles by combining in vivo two-photon Ca²⁺ imaging and holographic optogenetic stimulation in awake mice to study how increased activity of single cells affects the cortical network. We stimulated a small number of neurons sharing the same frequency preference alongside the presentation of a target pure tone, further increasing their tone-evoked activity. We found that other non-stimulated co-tuned neurons decreased their tone-evoked activity when the frequency of the presented pure tone matched their tuning property, while non-co-tuned neurons were unaffected. Activity decrease was greater for non-stimulated co-tuned neurons with higher frequency selectivity. Co-tuned and non-co-tuned neurons were spatially intermingled. Our results show that co-tuned ensembles communicated and balanced their total activity across the larger network. The rebalanced network activity due to external stimulation remained constant. These effects suggest that co-tuned ensembles in AC interact and rapidly rebalance their activity to maintain encoding network dynamics, and that the rebalanced network is persistent.