Neuronal requirements for swim initiation. A. Spontaneous hyperpolari zation of cell SIN1 and the subsequent cessation of its spiking activity does n ot initiate swimming.

A high frequency burst of action potentials in cell 204 neither inhibits cell SIN1 nor elicit swimming.

A spontaneous swim episode occurs only when spiking activity ceases in cell SIN1 and increases in cell 204. Note that changes in the activity levels of both cell SIN1 and cell 204 occur at approximately the same time and before the onset of swimming.