  Weakly electric fish are unique models in Neuroscience allowing
experimentalists to access, with non invasive techniques,a central nervous
system generated spatio-temporal electric pattern of pulses with roles in at
least two complex and not yet completely understood
abilities:electrocommunication and electrolocation. We developed an apparatus
to allow realistic stimulation and simultaneous recording of electric pulses in
freely moving Gymnotus carapo for very long periods-several days. Voltage time
series from a 3dimensional array of sensitive dipoles that detects electric
field in several positions underwater were digitized and home made real-time
software allowed reliable recording of pulse timestamps,independently of the
fish's position,and also to infer fish movement. A stimulus fish was mimicked
by a dipole electrode that reproduced the voltage time series of real
conspecific pulses,but according to timestamp sequences previously recorded
that could be chosen by the experimenter. Two independent variables were used
to analyze fish behavior:the entropy of the recorded timestamp sequences and
the movement of the fish inferred from pulse amplitude variability at each
detection dipole. All fish presented very long transient exploratory behavior
(about 8hours) when exposed to a new environment in the absence of stimuli.
After the transient there were several intervals(5min-2hours),in which entropy
vanished and no movement was observed, that could be associated with behavioral
sleeping. Our experiments also revealed that fish are able to discriminate
between real and random stimuli distributions by changing the timing
probability of the next discharge. Moreover,most fish presented behavioral
sleep periods when the artificial fish timestamp sequence was random,but no
fish showed any behavioral sleep period when the artificial fish fired
according to a real fish timestamp series.
