ELECTROSENSORY MODULATION OF ESCAPE RESPONSES

Once initiated, rapid escape responses of teleost fishes are thought t o be completed without additional sensory modification. This suggests that the motor program for a particular response is selected for by th e constellation of sensory cues existing at the time of the releasing stimulus. This paper presents initial evidence that a highly specializ ed, phylogenetically recent electrosensory system is integrated with a primitive motor system and allows an animal to continuously monitor i ts environment for producing accurate escape behaviors. Behavioral tes ting for directed startle responses in a ''Y-maze'' demonstrates that when presented immediately before an acoustic startle stimulus, electr ic fish (Eigenmannia virescens), direct their response away from the c ue (a transient shorting of their electric field). Thus, electrosensor y cues as brief as 100 ms provide directional information to the escap e motor network. In electric fish that are curarized to facilitate int racellular recording, the normal electric organ discharge is attenuate d. When al electronically generated replacement field of the same freq uency and amplitude as the fish's normal signal is shorted, a fast-ris ing, 7 ms latency post-synaptic potential is evoked from the Mauthner cell. Similar PSPs are generated by turning the replacement stimulus o n and off. In some recordings, removing the S1 replacement field elici ts a rebound of other afferent activity to the Mauthner cell; replacin g the field suppresses this activity.