ELECTRICALLY-EVOKED BEHAVIORS - AXONS AND SYNAPSES MAPPED WITH COLLISION TESTS

The properties of many axon bundles mediating electrically evoked resp onses have been described using double-pulse methods in behaving anima ls. The directly stimulated axons whose activation leads to the behavi or are defined by their refractory periods, conduction velocities and trajectories in those studies. In this review, new collision effects ( asymmetric collision) are described that locate synapses mediating tur ning and startle responses. The direction, time and reliability of tra nsmission are determined by the direction, time and strength of the as ymmetry. In systems mediating turning, five axon bundles have been loc alized with symmetric collision effects and evidence for two synapses has been provided with asymmetric collision effects. In systems mediat ing startle responses, three fast, reliable synapses have been located with asymmetric collision. Asymmetric collision effects between a lou d acoustic stimulus and a single electrical pulse in hindbrain sites d efine the timing and location of the acoustic volley that produces aco ustic startle. Therefore, when synapses are strong, circuit diagrams c an be constructed by use of collision tests in behaving animals.