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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 178 (1996), S. 453-462 
    ISSN: 1432-1351
    Keywords: Electric fish ; Gymnotiform fish ; Pulse-type electric fish ; Jamming avoidance response ; Temporal pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The sensory cues for a less known form of frequency shifting behavior, gradual frequency falls, of electric organ discharges (EODs) in a pulse-type gymnotiform electric fish, Rhamphichthys rostratus, were identified. We found that the gradual frequency fall occurs independently of more commonly observed momentary phase shifting behavior, and is due to perturbation of sensory feedback of the fish's own EODs by EODs of neighboring fish. The following components were identified as essential features in the signal mixture of the fish's own and the neighbor's EOD pulses: (1) the neighbor's pulses must be placed within a few millisecond of the fish's own pulses, (2) the neighbor's pulses, presented singly at low frequencies (0.2–4 Hz), were sufficient, (3) the frequency of individual pulse presentation must be below 4 Hz, (4) amplitude modulation of the sensory feedback of the fish's own pulses induced by such insertions of the neighbor's pulses must contain a high frequency component: sinusoidal amplitude modulation of the fish's own EOD feedback at these low frequencies does not induce gradual frequency falls. Differential stimulation across body surfaces, which is required for the jamming avoidance response (JAR) of wave-type gymnotiform electric fish, was not necessary for this behavior. We propose a cascade of high-pass and low-pass frequency filters within the amplitude processing pathway in the central nervous system as the mechanism of the gradual frequency fall response.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 174 (1994), S. 133-144 
    ISSN: 1432-1351
    Keywords: Corollary discharge ; Electric fish ; Gymnarchus ; Pacemaker ; Jamming avoidance response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Gymnarchus niloticus, a wave-type African electric fish, performs its jamming avoidance response by relying solely upon afferent signals and does not use corollary discharges from the pacemaker nucleus in the medulla which generates the rhythmicity of electric organ discharges. This is in sharp contrast to the mode of sensory processing found in closely related African pulse-type electric fishes where afferent signals are gated by corollary discharges from the pacemaker for the distinction of exafferent and reafferent stimuli. Does Gymnarchus still possess a corollary discharge mechanism for other behavioral tasks but does not use it for the jamming avoidance response? In this study, I recorded from and labeled medullary neuronal structures that either generate or convey the pacemaker signal for electric organ discharges to examine whether this information is also sent directly to any sensory areas. The pacemaker nucleus was identified as the site of generation of the pacemaking signal. The pacemaker neurons project exclusively to the lateral relay nucleus which, in turn projects exclusively to the medial relay nucleus. Neurons in the medial relay nucleus send unbranched axons to the spinal electromotoneurons. These neurons are entirely devoted to drive the electric organ discharges, and no axon collaterals from these neurons were found to project to any sensory areas. This indicates that Gymnarchus does not possess the neuronal hardware for a corollary discharge mechanism.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1351
    Keywords: Convergent evolution ; Neuronal computation ; Jamming avoidance response ; Phase comparison ; Electric fish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract An African electric fish, Gymnarchus, and a South American electric fish, Eigenmannia, are believed to have evolved their electrosensory systems independently. Both fishes, nevertheless, gradually shift the frequency of electric organ discharge away when they encounter a neighbor of a similar discharge frequency. Computational algorithms employed by Gymnarchus for this jamming avoidance response have been identified in this study for comparison with those of extensively studied Eigenmannia. 1. Gymnarchus determines whether it should raise or lower its discharge frequency based solely upon the signal mixture of its own reafferent and the exafferent signal from a neighbor, and does not internally refer to the pacemaker command signal which drives its own discharge. 2. The signal mixture is analyzed in terms of the time courses of amplitude modulation and phase modulation at each area of the body surface. 3. Phase of the signal mixture at each area is compared with that of another area for the detection of phase modulation. 4. Unambiguous information necessary for the jamming avoidance response is extracted by integrating information from all body areas each of which yields ambiguous information. 5. These computational features are identical to those of Eigenmannia, suggesting that the neural circuit for jamming avoidance responses may have evolved from preexisting mechanisms for electrolocation in both fishes.
    Type of Medium: Electronic Resource
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