Fig. 5.

Absence of change in sliding estimate ofp during homosynaptic depression. Plots inA and B are from one experiment and illustrate how the slopes of sliding m andp were derived and normalized. Sliding p(calculated from Eq. 1, with W = 0.65) andm were determined for groups of five responses, moving one response at a time. In A, the approximately linear decline in sliding m was fit by linear regression, as was the corresponding portion of the plot of sliding p.B illustrates normalization of the slopes of slidingm and p to permit direct comparison of the slopes; the slopes were normalized by setting the respectivey-intercepts equal to 1. C is a plot of the normalized slope of sliding p against the normalized slope of sliding m in nine experiments on cultures in normal ASW medium. The two filled circles represent experiments in which the average p was ∼0.3;p in all of the other experiments was >0.6. Theline represents a slope of zero for slidingp. D, For experiments without an independent estimate of the quantal amplitude and variance, the variance (V) and mean (M) of the EPSP amplitude were used to test for changes in p; no change in the ratioV/M implies no change in p(see Results). The line represents a slope of zero for sliding V/M.