Information processing in the neuron requires spatial summation of synaptic inputs at the dendrite. In CA1 pyramidal neurons of the hippocampus, a brief period of correlated pre- and postsynaptic activity, which induces long-term potentiation (LTP) or long-term depression (LTD), results in a persistent increase or decrease in the linearity of spatial summation, respectively. Such bidirectional modification of the summation property is specific to the modified input and reflects localized dendritic changes involving I(h) channels and NMDA receptors. Thus, correlated pre- and postsynaptic activity alters not only the strength of the activated input but also its dendritic integration with other inputs.