for helpful discussions, and M. Teruel for setting up the electroporation apparatus and the rapid image capturing system. Synthesis of caged InsP 3 was performed in the laboratory of J. Most natural actions are accomplished with a seamless combination of individual movements. Such coordination poses a problem: How does the motor system orchestrate multiple movements to produce a single goal-directed action? The results from current experiments suggest one possible solution. Oculomotor neurons

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... the superior colliculus of a primate responded to mismatches between eye and target positions, even when the animal made two different types of eye movements. This neuronal activity therefore does not appear to convey a command for a specific type of eye movement but instead encodes an error signal that could be used by multiple movements. The use of shared inputs is one possible strategy for ensuring that different movements share a common goal.