Anatomical structure alone cannot predict function BEHAVIORAL AND BRAIN SCIENCES

The central hypothesis of the target article that tidal waves of parallel fiber excitation precisely activate Purkinje cell spiking is hard to reconcile with recent neurophysiological and modeling data. The assumed pattern of mossy fiber input seems unrealistic, inhibition is likely to interfere with the proposed excitatory responses, and moreover, computer simulations show that the Purkinjecell is a poor coincidence detector. While providing an interesting framework for understanding cerebellar function, the theory proposed by Braitenberg and colleaguesis limited mostly to neuroanatomical speculation. In this comment we will show that recent physiological and modeling data cast doubt on three essential components of the theory: the pattern of mossy fiber input, the purely lateral inhibition and the sensitivity of Purkinje cells to waves of parallel fiber input. Unless major enhancements to the theory are made, and direct experimental evidence in vivo is found, we find it unlikely that the cerebellum is operatin