How does the brain track time intervals? A new paper in the journal Neuron by Dean Buonomano of the UCLA Brain Research Institute proposed a theory that time is measured not like a clock, but by tracking changes in neurons as they propagate through the brain following some kind of signal or event, such as hearing a sound that could be either the word "the" or the start of "this." Imagine throwing a pebble into a pond, he says; you could calculate how much time has gone by at any moment by comparing how far the ripples have spread with a set of reference pictures for different intervals. The brain does something similar, he believes-- and within a 10 percent margin of error. Measuring small intervals could prove useful in other sensory modes, such as touch. This insight could someday be useful in treating conditions, such as dyslexia, that involve impairments to language.