High somato-dendritic coupling of V1 layer 5 neurons independent of behavioural state and visual stimulation

Abstract Active dendritic conductances impact the integration of synaptic inputs. However, the extent to which dendrites act as independent computational subunits in vivo, remains unclear. We imaged calcium signals in the soma, trunk and distal tuft dendrites of individual layer 5 pyramidal neurons in the primary visual cortex of awake mice, both in darkness and during visual stimulation, while the animal was either running or stationary. We found highly correlated calcium transients in all imaged apical tuft branches and throughout all neuronal compartments (soma, trunk, tuft). However, the frequency of calcium transients was found to decrease in a distance- and amplitude-dependent manner from soma to apical tuft. Visual stimulation and locomotion increased global apical tuft activity but did not alter the coupling between soma and apical tuft. In the apical tuft, branch-specific activity was rare, limited to the smallest calcium transients and independent of visual stimulation and locomotion.