Fifty years of a command neuron: the neurobiology of escape behavior in the crayfish

Fifty years ago C.A.G. Wiersma established that the giant axons of the cray fish nerve cord drive tail-flip escape responses. The circuitry that includ es these giant neurons has now become one of the best-understood neural cir cuits in the animal kingdom. Although it controls a specialized behavior of a relatively simple animal, this circuitry has provided insights that are of general neurobiological interest concerning matters as diverse as the id entity of the neural substrates involved in making behavioral decisions, th e cellular bases of learning, subcellular neuronal computation, voltage-gat ed electrical synaptic transmission and modification of neuromodulator acti ons that result from social experience. This work illustrates the value of studying a circuit of moderate, but tractable, complexity and known behavio ral function.