The threshold for detecting temperature changes in a spider thermoreceptor. Ehn, Rudolf and Harald Tichy. Institut f[umlaut]ur Zoologie, Universit[umlaut]at Wien, Biologiezentrum, Althanstrasse 14, A-1090 Wien, Austria.
APStracts 3:0094N, 1996.
SUMMARY AND CONCLUSIONS
1. The threshold for detecting a change in temperature of a warm receptor in the wandering spider Cupiennius salei was determined by means of its frequency-dependent noise. To accomplish this, the warm receptor was regarded as a linear system consisting of two components, an amplifier (gain of the frequency response) and noise at its input added to the temperature stimulus (input noise density). 2. The frequency response was investigated with sinusoidal temperature modulations at frequencies between 0.05 ? Hz and 12.8 ? Hz. The gain increased by 3.5 ? dB/octave in the frequency range between 0.05 ? Hz and 6.4 ? Hz, from 0.19 degrees C-1 to 3.1 degrees C-1. However, at the highest frequency, 12.8 ? Hz, the gain was reduced. 3. The noise density of the warm receptor was measured by the RMS noise amplitude of the gain. The output noise density of the warm receptor, which describes the noise density of the gain, was constant at 0.2 ? Hz-0.5 in the 0.05 ? Hz to 6.4 ? Hz range, and increased at higher frequencies. The input noise density, given by the ratio of output noise density to gain, decreased by -2.7 ? dB/octave between 0.05 ? Hz and 6.4 ? Hz, from 1.1 degrees C*Hz-0.5 to 0.12 degrees C*Hz-0.5. 4. To define the threshold for detection of temperature changes from the input noise density, the energy of the threshold was equated to the energy of the noise. Assuming a signal-to-noise ratio of 1 and an upper limiting frequency of 10 ? Hz, the threshold estimated for the wandering spider Cupiennius ranges from 0.6 degrees C to 0.08 degrees C, depending on whether the input from only one or all 70 warm receptors of the ten tarsal organs are combined.

Received 12 June 1995; accepted in final form 14 May 1996.
APS Manuscript Number J377-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 June 96