Dynamics of Neurons Controlling Movements of a Locust Hind Leg: Wiener
Kernel Analysis of the Responses of Proprioceptive Afferents.
Kondoh, Y., J. Okuma, and P. L. Newland.
Wako Research Center, Wako, Saitama 351_01, Japan; and Department of
Zoology, University of Cambridge, Cambridge CB2 3EJ, England.
APStracts 2:0046N, 1995.
SUMMARY AND CONCLUSIONS
1. The response properties of proprioceptive sensory neurons providing input
to the local circuits controlling leg movements of the locust have been
analysed by the Wiener kernel method. The proprioceptor, the femoral
chordotonal organ, encodes the position and movements of the tibia about the
femorotibial joint. 2. Intracellular recordings were made from sensory
neurons while the apodeme of the organ was moved with a band-limited Gaussian
white noise signal with a cutoff frequency of 27, 58, or 117 Hz. To define the
input-output characteristics of the neurons, the first- and second-order
Wiener kernels were computed by a cross-correlation between the spike response
of the afferents and the white noise stimulus. 3. White noise stimulation
elicited sustained spiking in 50 out of 54 afferents throughout the 20-s
periods of stimulation and recording. The first-order kernels, the linear
response properties, of these afferents were of six basic types that were
dependent on the cutoff frequency of the white noise stimulus. These included
1 ) flexion-sensitive afferents that were primarily position sensitive
irrespective of stimulus frequency, 2 ) flexion-sensitive afferents that were
position sensitive at low frequencies but also coded velocity at higher
frequencies, 3 ) flexion-sensitive afferents that coded velocity at all
stimulus frequencies, 4 ) flexion-sensitive afferents that coded velocity at
low stimulus frequencies but also acceleration at high frequencies, 5 )
extension-sensitive afferents that coded velocity at all stimulus frequencies,
and 6 ) extension-sensitive afferents that coded velocity at low stimulus
frequencies and acceleration at high frequencies. A seventh type contained the
four remaining afferents that adapted rapidly to the stimulus within 3_5 s.
These were all extension-acceleration_sensitive irrespective of stimulus
frequency. 4. The gain curves (produced by Fourier transform of the 1st-
order kernels) and the power spectra of the linear models (produced by
convolving the 1st-order kernels with the white noise) demonstrated that
responses in the position-sensitive afferents are representative of a constant
gain low-pass filter with a cutoff frequency of _80 Hz, whereas those in the
velocity- and acceleration-sensitive afferents are band passed, having peaks
at 80 Hz. 5. The main nonlinearity was a signal compression in which the
diagonal peak(s) of the second-order nonlinear kernels offset one or more
peaks of the first-order kernels and represents a rectification or directional
sensitivity of the afferents. 6. A summation of the first- and second-order
models produced by convolving the stimulus input with the first- and second-
order kernels could predict the occurrence of 90% of spikes at best. Thus the
two lower order kernels can characterize, in detail, the response dynamics of
the afferents.
Received 5 July 1994; accepted in final form 18 January 1995.
APS Manuscript Number J398-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 3 April 1995.