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  • Electrolocation  (1)
  • Hearing  (1)
  • Tonotopy  (1)
  • 1
    ISSN: 1432-1106
    Keywords: Electric fish ; Electrolocation ; Single unit recording ; Mesencephalon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Extra- and intracellular recordings from single units in the magnocellular mesencephalic nucleus (MMN) of the torus semicircularis, related to the fast electrosensory system are reported for the weakly electric fish Gymnotus carapo (Gymnotidae). 2. The non-spontaneously active units responded with single action potentials to the electric organ discharge (EOD) and to artificial electrical pulses with a very short latency of 0.8–1.5 ms. This strongly suggests, in agreement with morphological data, that transmission takes place through electrical synapses. 3. The dynamic range (probability and latency of the single action potential) of the response is extremely narrow and about the same as found in the relevant electrosensory fibres. Intracellular stimulation gives the same response characteristics and dynamic range. 4. The recovery of the response was studied in detail using different stimulus combinations of double pulses at varying delays. Under all conditions, the recovery period to evoke a test response after a conditioning stimulus and response increased in length with the strength of the conditioning stimulus. Inversely, the conditioning stimulus to prevent the unit from firing again had to be stronger as the delay between the two stimuli was increased. 5. Since there is no evidence of neural inhibition causing the long lasting and graded recovery characteristics for MMN units, an attempt was made to explain the findings by classical neurophysiological considerations adapted for electrical synaptic transmission (“current sink” theory). 6. This neural mechanism means that, if at all, the relatively weaker stimulus is not responded to, which protects the fish from being jammed by external pulses of physiological amplitude. In contrast, very strong foreign pulses can completely abolish responses to own EODs especially when timed appropriately. Both effects are discussed in view of their significance for the fish's electrosensory system and communication.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1351
    Keywords: Hearing ; Chiroptera ; Desmodus Inferior colliculus ; Tonotopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Within the tonotopic organization of the inferior colliculus two frequency ranges are well represented: a frequency range within that of the echolocation signals from 50 to 100 kHz, and a frequency band below that of the echolocation sounds, from 10 to 35 kHz. The frequency range between these two bands, from about 40 to 50 kHz is distinctly underrepresented (Fig. 3B). 2. Units with BFs in the lower frequency range (10–25 kHz) were most sensitive with thresholds of -5 to -11 dB SPL, and units with BFs within the frequency range of the echolocation signals had minimal thresholds around 0 dB SPL (Fig. 1). 3. In the medial part of the rostral inferior colliculus units were encountered which preferentially or exclusively responded to noise stimuli. — Seven neurons were found which were only excited by human breathing noises and not by pure tones, frequency modulated signals or various noise bands. These neurons were considered as a subspeciality of the larger sample of noise-sensitive neurons. — The maximal auditory sensitivity in the frequency range below that of echolocation, and the conspicuous existence of noise and breathing-noise sensitive units in the inferior colliculus are discussed in context with the foraging behavior of vampire bats.
    Type of Medium: Electronic Resource
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