The evaluation of electroreceptive feedback in a gymnotoid fish with pulse-type electric organ discharges

Abstract

How does a gymnotoid electric fish with pulse-type electric organ discharges (EODs) detect specific novelties in electroreceptive feedback from its own EODs if it is contaminated by EODs of a neighbor? To answer this question, experiments were performed on intact as well as on curarized animals. Specimens were curarized and their silenced EODs replaced by artificial pulses, S1, in order to dissociate electroreceptive afferences 1 from the activity of the electric organ pacemaker. The animal's ability to detect small, local distortions in its own EOD field as well as in a substituted S1-field was tested while various patterns of pulses, S2, mimicking EODs of a neighbor, were presented (Fig. 1). The following results were obtained: 1. The animal evaluates electroreceptive afferences without reference to the pacemaker which normally drives its EODs, the main source of electroreceptive afferences. 2. Signals interfering with the animal's EOD, or S1, will impair the detection of specific novelties to the extent that they cause transient alterations in electroreceptive afferences over the course of several successive EODs. Foreign pulses which coincide with or narrowly precede several successive EODs are more detrimental than noncoincident pulses (Figs. 2–5, 9). 3. The animal adapts to maintained alterations of its electroreceptive afferences in the course of seconds and thereby regains its ability to detect novelties in a maintained jamming regime which allows electroreceptive afferences to stabilize to a new state (Fig. 4). 4. Detection of novelties in curarized fish improves to the extent that the EOD substitute, S1, is presented at a high and regular rate (Figs. 6. 7). High and regular EOD rates, which are commonly observed in novel situations, should therefore enhance the animal's ability to detect the appearance of objects in its environment. 5. The Jamming Avoidance Response (JAR) prevents successive EODs from coinciding with foreign pulses of a similar repetition rate. Such coincidences disturb electroreceptive afferences most severely. By avoiding coincidences, the JAR stabilizes these afferences and thereby enhances the detection of specific novelties in the presence of conspecifics (Fig. 10).