Cover legend: Photograph of a biocytin-filled layer 5 pyramidal cell from the prefrontal cortex. Whole-cell recordings were obtained simultaneously from the cell body and axon of this cell. Injection of a current pulse initiated action potentials in the axon initial segment (yellow traces), and these backpropagated into the soma (red traces). The phase plots of dV/dt versus membrane potential (overlays) illustrate the higher variability in apparent spike threshold in the soma versus the axon initial segment. This high variability results from the properties of backpropagating action potentials. For more information, see the article by Yu et al. in this issue (pages 7260–7272).