Coding of amplitude information by the time-locked electrosensory system of Brachyhypopomus
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1
University of Virginia, Department of Biology, United States
A pulse-type gymnotiform electric fish, Brachyhypopomus gauderio, emits short electrical pulses from its electric organ in the tail and senses the feedback signals with the tuberous electroreceptors in the skin for electrolocation and electrocommunication. The feedback signals are captured and processed by two distinct pathways, the amplitude and time-locked electrosensory systems. While the amplitude system is driven by the electroreceptors, the burst duration coders, which generate action potentials at variable rates according to the amplitude of the electrosensory signals, the time-locked system is driven by the pulse markers, which generate a single action potential in response to a feedback pulse regardless of its amplitude. The response latency of the action potentials of pulse markers and their ascending higher order time-locked neurons in the midbrain, however, may depend on the amplitude of stimulus pulses. In this study, (1) we measured the amplitude of the self stimulation by fish's own electric organ discharges in an in vivo preparation, (2) recorded the latencies and accuracy (jitter) of time-locked neurons in the midbrain in response to artificial electric organ discharges with various waveforms and amplitudes, and (3) compared the slope of the amplitude-latency function with the sensitivity of a behavioral response to time differences between feedback pulses. The time-locked neurons in the midbrain fired their action potentials with short latency (~0.9 msec) and with accurate timing (a few microseconds). The natural waveform, polarity (outward monophasic waveform), and higher repetition rates of the stimulus pulses produced smaller jitter. The slope of the amplitude-latency function indicated that amplitude modulation of sensory signals at 20% shifted the latency of the midbrain time locked neurons by ~40 microseconds on average, which was large enough to cause novelty responses. Novelty responses were recorded when stimulus pulses with equal amplitudes were delivered with microsecond time differences. We propose that the timing system of Brachyhypoopomus encodes and utilizes time information in the microsecond range which are resulted not only from capacitance of electrolocation objects but also from the changes in amplitude of feedback signals caused by resistive components of electrolocation objects, surrounding environment, and relative geometrical positions of the electric organ of itself or neighboring fish.
Keywords:
Electric Fish,
electrosensory system,
Neural coding,
phase locked neurons,
time locked neurons
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensory: Electrosensory
Citation:
Kawasaki
M
(2012). Coding of amplitude information by the time-locked electrosensory system of Brachyhypopomus.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00209
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Received:
29 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Prof. Masashi Kawasaki, University of Virginia, Department of Biology, Charlottesville, VA, 22904, United States, mk3u@virginia.edu