Gj. Rose et al., RESPONSES OF ELECTROSENSORY NEURONS IN THE TORUS SEMICIRCULARIS OF EIGENMANNIA TO COMPLEX BEAT STIMULI - TESTING HYPOTHESES OF TEMPORAL FILTERING, Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 175(4), 1994, pp. 467-474
The weakly electric fish, Eigenmannia, changes its frequency of electr
ic organ discharges (EODs) to increase the frequency difference betwee
n its EODs and those of a jamming neighbor. This jamming avoidance res
ponse is greatest for frequency differences (i.e., beat rates) of appr
oximately 4 Hz and barely detectable at beat rates of 20 Hz. A neural
correlate of this behavior is found in the torus semicircularis, where
most neurons act as low-pass or band-pass filters over this range of
beat rates. This study examines two mechanisms that could possibly und
erlie low-pass temporal filtering: 1) Inhibition by a 'high-pass' inte
rneuron. 2) Voltage and time-dependent conductances associated with li
gand-gated channels. These mechanisms were tested by recording intrace
llularly while employing stimuli consisting of simultaneous low and hi
gh beat rates. A neuron's response to the low beat rate was not dimini
shed by the addition of the higher frequency jamming signal (thereby s
uperimposing a high rate of amplitude and phase modulation onto the lo
wer rate), and the 'inhibitory interneuron' hypothesis is, therefore,
not supported. Also, the responses to the high beat rate were not faci
litated during maintained depolarization in response to the low beat r
ate. In some cases, particularly band-pass neurons, accommodation proc
esses appeared to contribute to the decline in the amplitude of psps a
t high beat rates.