  The origin of differences in the magnetic responses of
Pr$_{1-x}$LaCe$_x$CuO$_4$ with $x=0.11-0.12$ and moderately doped $p$-type
cuprates is investigated using the t-J model, the Mori projection operator
technique and dispersions of charge carriers derived from photoemission
experiments. These differences are related to the proximity of the former
crystal to the boundary of the antiferromagnetic phase and to the remoteness of
$p$-type compounds from it. This leads to different nesting vectors of the
low-frequency equi-energy contours of carrier dispersions in these crystals.
The strong nesting with the antiferromagnetic momentum as the nesting vector
produces the commensurate low-frequency response and the coexistence of two
spin-excitation branches in Pr$_{1-x}$LaCe$_x$CuO$_4$, while incommensurate
nesting vectors in $p$-type crystals lead to the incommensurate low-frequency
response and the hourglass dispersion of susceptibility maxima.
