Cover picture: Snapshots of the distribution of membrane potential in a cat cortical (layer VI) pyramidal neuron during simulated in vivo activity. The colors indicate the membrane potential (from violet, 80 mV, to yellow, 25 mV; see scale). Time runs from left to right, then top to bottom (steps of 0.5 msec, except for the first frame, which was taken 4 msec earlier). The simulation shows a dendritic action potential that propagates forward to the soma and evokes a backpropagating action potential in all other dendrites. These forward-propagating action potentials may play an important role in the integrative properties of pyramidal neurons during in vivo-like states. For details, see the article by Rudolph and Destexhe in this issue (pages 2466–2476).