To investigate synaptic events underlying sensory perception, we made whole-cell membrane potential recordings of barrel cortex neurons in awake mice while recording whisker-related behavior. During quiet periods, we recorded slow, large-amplitude membrane potential changes, which switched during whisking to small, fast fluctuations that were correlated with whisker position. Robust subthreshold responses were evoked by passive whisker stimulation during quiet behavior and by active whisker contact with an object.