Jr. Mckibben et al., DIRECTIONAL SENSITIVITY OF TUBEROUS ELECTRORECEPTORS - POLARITY PREFERENCES AND FREQUENCY TUNING, Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 173(4), 1993, pp. 415-424
This paper examines the directionality of tuberous electroreceptor res
ponses and relates them to a polarity bias seen for passive electroloc
ation by electric fish (Hypopomus). We recorded from Burst Duration Co
ders (BDCs) while stimulating with 1 kHz single period sine waves with
electric fields oriented horizontally in different directions. Electr
oreceptors have figure-8 directional sensitivity profiles with two, us
ually unequal lobes of sensitivity separated by 180-degrees. For most
units the larger lobe points inward, while for a few, the lobes are sy
mmetrical or the larger lobe points outward. The differences correlate
with differences in frequency tuning of the receptors. We can alter,
and even reverse, the directional asymmetry of a single unit by changi
ng the frequency of the stimulus. Two general response profiles result
, with two corresponding classes of tuning curves. The degree of asymm
etry varies with position on the, body surface. The asymmetries and th
e effects of stimulus frequency and of tuning can be modeled with a li
near/non-linear/linear cascade filter. The behavioral preference for a
pproaching the head end (+) of an electrode is difficult to understand
in light of the asymmetry of responses we report for amplitude-coding
BDCs but can be understood by reference to the time-coding Pulse Mark
er (PM) receptors.