Local current spread in electrically compact neurons of the fly

Analyses of active and passive membrane properties predict an asymmetry in the spread of electrical current through a neuron. Simulated current inject ion into a large-diameter compartment of a biophysically realistic model ne uron causes a local potential shift that can spread throughout the cell. In contrast, causing the same local potential shift in the dendritic tip of t he same neuron results in only minimal changes in electrical potential in t he rest of the cell. Using calcium as a reporter of electrical activity in neurons in the fly's lobula plate we find that current injected into the th ick axon caused depolarization throughout the cell, whereas activation of a dendritic region remained local. These results have important implications for the ability of integrating neurons to perform local computations of sy naptic input without additional hardware. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.