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