Nonsensory variables strongly influence neuronal activity in the adult mouse primary visual cortex. Neuronal responses to visual stimuli are modulated by behavioural state, such as arousal and motor activity, and are shaped by experience. This dynamic process leads to neural representations in the visual cortex that reflect stimulus familiarity, expectations of reward and object location, and mismatch between self-motion and visual-flow. The recent development of genetic tools and recording techniques in awake behaving mice has enabled the investigation of the circuit mechanisms underlying state-dependent and experience-dependent neuronal representations in primary visual cortex. These neuronal circuits involve neuromodulatory, top-down cortico-cortical and thalamocortical pathways. The functions of nonsensory signals at this early stage of visual information processing are now beginning to be unravelled.

Active dendrites impact sensory processing and behaviour. However, it remains unclear how active dendritic integration relates to somatic output in vivo. We imaged semi-simultaneously GCaMP6s signals in the soma, trunk and distal tuft dendrites of layer 5 pyramidal neurons in the awake mouse primary visual cortex. We found that apical tuft signals were dominated by widespread, highly correlated calcium transients throughout the tuft. While these signals were highly coupled to trunk and somatic transients, the frequency of calcium transients was found to decrease in a distance-dependent manner from soma to tuft. Ex vivo recordings suggest that low-frequency back-propagating action potentials underlie the distance-dependent loss of signals, while coupled somato-dendritic signals can be triggered by high-frequency somatic bursts or strong apical tuft depolarization. Visual stimulation and locomotion increased neuronal activity without affecting somato-dendritic coupling. High, asymmetric somato-dendritic coupling is therefore a widespread feature of layer 5 neurons activity in vivo.

No abstract

17Active dendrites impact sensory processing and behaviour. However, it remains unclear how 18 active dendritic integration relates to somatic output in vivo. We imaged semi-simultaneously 19 GCaMP6s signals in the soma, trunk and distal tuft dendrites of layer 5 pyramidal neurons in 20 the awake mouse primary visual cortex. We found that apical tuft signals were dominated by 21 widespread, highly correlated calcium transients throughout the tuft. While these signals 22 were highly coupled to trunk and somatic transients, the frequency of calcium transients was 23 found to decrease in a distance-dependent manner from soma to tuft. Ex vivo recordings 24 suggest that low-frequency back-propagating action potentials underlie the distance-25 dependent loss of signals, while coupled somato-dendritic signals can be triggered by high-26 frequency somatic bursts or strong apical tuft depolarization. Visual stimulation and 27 locomotion increased neuronal activity without affecting somato-dendritic coupling. High, 28 asymmetric somato-dendritic coupling is therefore a widespread feature of layer 5 neurons 29 activity in vivo. 30 2 31 698We thank the GENIE Program and the Janelia Research Campus, specifically V. Jayaraman, R.