The Year of the Dendrite

Octopus-like neurons, the cells of the brain, typically have many input “arms”—the dendrites, which receive signals from other neurons—and one output arm, the axon. Two new reports in this week's Science show that the dendrites process information in a manner even more complex than expected. In his Perspective, Sejnowski explains how the observations of Magee and Johnston ( p. 209 ) and Markram et al. ( p. 213 ) on backpropagating action potentials illuminate the mechanism of Hebbian learning, the synaptic strengthening that occurs when a receiving neuron is active at the same time that a signal comes in.