Neural correlates of a nonjammable electrolocation system.

The detection of objects by the electrosensory system of weakly electric fish is subject to electrical interference such as that produced by the electric organ discharges emitted by neighboring electric fish. Most electric fish species have a behavioral reflex, the jamming avoidance response, which protects their electrolocation system against jamming. Sternopygus is unique in that it has no jamming avoidance response, yet can electrolocate even in the presence of jamming. It appears that Sternopygus protects electrolocation not by a behavioral strategy but by first-order central processing mechanisms that can distinguish between localized changes in the amplitudes of electric organ discharges caused by objects and large-field amplitude modulations caused by jamming. This mechanism acts as a local contrast detector and is functionally similar to the one used by retinal cells to respond to local contrast in light but not to overall changes in illumination.