The crayfish lateral giants as command neurons for escape behavior.

The lateral giants (LGs) of the crayfish have often been described as command neurons. Recently, questions have arisen as to the definition of command neurons and as to whether the LGs are necessary for tailflips. We find that in an isolated abdomen preparation the LGs are necessary; temporarily blocking the LGs by hyperpolarization eliminates the tailflip flexor muscle output normally elicited by stimulation of the sensory afferents. However this demonstration of the LGs' necessity does not establish the LGs as the decision point of the behavior, for the LGs might be driven by a large input from a preceding decision neuron. We have checked for such an input by plotting the size of the EPSP produced in the hyperpolarized LG by various stimulus levels near spike threshold. We find no evidence for a large driving input near spike threshold. We conclude that the LGs have most of the features of command neurons.