  In the presence of a quark chemical potential, a magnetic field induces an
axial current in the direction of the magnetic field. We compute this current
in the Sakai-Sugimoto model, a holographic model which, in a certain limit, is
dual to large-N_c QCD. We also compute the analogous vector current, for which
an axial chemical potential is formally introduced. This vector current can
potentially be observed via charge separation in heavy-ion collisions. After
implementing the correct axial anomaly in the Sakai-Sugimoto model we find an
axial current in accordance with previous studies and a vanishing vector
current, in apparent contrast to previous weak-coupling calculations.
