  We estimate the nuclear medium modifications of the quark contribution to the
bound nucleon spin sum rule, J^{q*}, as well as the separate helicity, \Delta
\Sigma*, and the angular momentum, L^{q*}, contributions to J^{q*}. For the
calculation of the bound nucleon generalized parton distributions (GPDs), we
use as input the bound nucleon elastic form factors predicted in the
quark-meson coupling model. Our model for the bound nucleon GPDs is relevant
for incoherent deeply virtual Compton scattering (DVCS) with nuclear targets.
We find that the m5Aedium modifications increase J^{q*} and L^{q*} and decrease
\Delta \Sigma* compared to the free nucleon case. The effect is large and
increases with increasing nuclear density \rho. For instance, at
\rho=\rho_0=0.15 fm^{-3}, J^{q*} increases by 7%, L^{q*} increases by 20%, and
\Delta \Sigma* decreases by 17%. These in-medium modifications of the bound
nucleon spin properties may be understood qualitatively in terms of the
enhancement of the lower component of the quark Dirac spinor in the nuclear
medium.
