Journal of Neurophysiology, Vol 65, Issue 1 67-75, Copyright © 1991 by APS
The influence of noise on quantal EPSP size obtained by deconvolution in spinal motoneurons in the cat
H. P. Clamann, M. S. Rioult-Pedotti and H. R. Luscher
Department of Physiology, University of Bern, Switzerland.
1. The amplitudes of quantal components that make up single-fiber
excitatory postsynaptic potentials (EPSPS) were determined by a
deconvolution technique and by simulation studies and were compared with
the background noise. 2. A strong correlation was found between the sizes
of EPSP quantal components and the standard deviation of the noise from
which the data were extracted by deconvolution. A similar correlation was
then shown in published data from several other laboratories. 3. EPSPS
having amplitudes less than 100 microV were recorded that had little or no
variance in their amplitudes. Most of these EPSPS showed a much smaller
peak variance than would be expected if they fluctuated among amplitudes in
steps of approximately 100 microV--the proposed mean value for the
amplitude of the quantal EPSP. 4. Deconvolution of simulated data with the
maximum likelihood algorithm resulted in the suppression of components less
than 1.5 SD of the background noise. The remaining components were
approximately equally spaced. No way was found to detect this error, and
rejection of deconvolved data with components less than 1.5 noise SD did
not eliminate it. The resulting erroneous data showed a strong correlation
between the amplitudes of the components obtained and the noise standard
deviation. 5. It is concluded that at least some EPSPS generated by single
Ia-afferents on motoneurons are composed of quantal components
significantly less than 100 microV and that deconvolution procedures are
not capable of detecting such small components.
