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Neighboring neurons in motor cortex exhibit diverse selectivity during sensation, movement preparation, and movement execution. Neuronal selectivity could emerge from diverse mechanisms, including selective connectivity and nonlinear interactions of synaptic inputs in dendrites. We studied dendritic integration in the anterior motor cortex of mice performing a tactile discrimination task with a delayed response (Guo and Li et al., 2014). We constructed a two-photon microscope that allows rapid (~15 Hz) imaging of up to 300 µm of contiguous dendrite while resolving calcium transients in individual dendritic spines. Two galvanometers and a remote focusing mirror (Botcherby et al., 2008) steer 16 kHz lines (24 µm extent) produced by a resonant mirror arbitrarily in three dimensions. Pyramidal neurons were labeled sparsely with GCaMP6f in transgenic mice. We imaged spine and dendritic calcium transients, as well as somatic calcium transients associated with action potentials. We developed methods to computationally remove the influence of backpropagating action potentials (bAPs), which allowed us to quantify the selectivity of spines and dendritic segments during sensation, movement preparation, and movement execution. Nearby spines and dendritic segments share similar selectivity (length constant of signal correlation, ~30 µm). This clustering was more often seen in distal than in proximal dendrites. Using a measure of local autocorrelation, we also found that this reflects distinct “hotspot” locations on the dendrite where nearby dendrite and spines are co-active in time. Hotspot selectivity was correlated with the behavioral selectivity of somatic spikes, suggesting that these locations may have privileged influence over the output of the cell.