Different scientists give different definitions of “time.” Neuroscientists measure brain activity using an abscissa of time (action potentials per unit of time), with the implicit understanding that the brain can make computations based on a perfect clock. But what clock does the brain use to measure its own activity? To make matters more complex, all perceptual phenomena are accompanied by a feeling of the passage of time. Our ongoing studies show that the brain creates a sense of the duration of an experience using, as a clock, the very same neuronal activity evoked by that experience. Thus, for instance, the firing of neurons in somatosensory cortex creates a tactile percept but, if rats are trained to judge the duration of a tactile stimulus, manipulating sensory cortical firing creates a distortion of the sense of time. I will explore this and other perceptual distortions that to arise from the complex meaning of time in brain computations.