Report of interval timing or action?

Xu et al. (1) argue that the medial prefrontal cortex (mPFC) is involved in interval timing. However, we believe that their data can be explained by the hypothesis that the mPFC simply responds to port exit: the action indicating the expiry of timed intervals. To illustrate our argument, imagine the following addition to the experiment: a flash of light is presented to animals when they exit the waiting port. Say that neurons in the primary visual cortex (V1) respond to the light, as expected. If one were to plot a peri-event time histogram (PETH) of these responses aligned to the sound onset (as in figure 3 of ref. 1), neurons …