THE INFLUENCE OF NOISE ON QUANTAL EPSP SIZE OBTAINED BY DECONVOLUTION IN SPINAL MOTONEURONS IN THE CAT

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 < 100 mu-V 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 mu-V-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 < 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 < 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 < 100 mu-V and that deconvolution procedures are not capable of detecting such small components.