Pyramidal neurons have prominent apical dendrites that are hypothesised to modulatesomatic output. In the visual cortex, apical dendrites may receive contextual signals via top-down inputs and local inhibition. It is not known, however, what causal effects they play indriving or suppressing somatic activity, and how they shape a neuron’s visual tuning.We recorded activity of pyramidal neurons sparsely expressing GCaMP7s in layer 5 of visualcortex in awake mice before and after pruning their apical dendrites with two-photondendrotomy. Together with the neuron’s receptive field and orientation/direction selectivity,we measured properties that depend on sensory and behavioural context: size tuning andcorrelation with facial movements. Then we repeated these measurements after pruning theapical dendrite of 51% neurons (n=118, N = 6), sparing the others as controls.Pruning the apical dendrite significantly reduced all visual response by a factor of 0.65 (p<0.001) compared to controls, but did not affect orientation/direction selectivity, nor change theneurons’ correlation with facial movements. It did not decrease surround suppression:neurons preferring small stimuli did not change their tuning. However, it reduced responsesto large stimuli in neurons that preferred those stimuli.In conclusion, the apical dendrite appears to deliver visual drive from distant parts of visualspace to the neurons that prefer large stimuli. Additionally, it amplifies responses to stimuliwithin the receptive field. Finally, the apical dendrite does not seem to carry behaviouralsignals, which may instead arise from inputs to the basal dendrites.