  Using the Hellmann--Feynman theorem we analyze the contribution of the
different terms of the nucleon-nucleon interaction to the spin symmetry energy
of neutron matter. The analysis is performed within the microscopic
Brueckner--Hartree--Fock approach using the Argonne V18 realistic potential
plus the Urbana IX three-body force. The main contribution to the spin-symmetry
energy of neutron matter comes from the S=0 channel, acting only in the
non-polarized neutron matter, in particular the $^1S_0$ and the $^1D_2$ partial
waves. The importance of correlations in spin-polarized neutron matter is
estimated by evaluating the kinetic energy difference between the correlated
system and the underlying Fermi sea.
