  Using the two-particle self-consistent approach and cluster perturbation
theory for the two-dimensional t-t'-t''-U Hubbard model, we discuss weak- and
strong-coupling mechanisms for the pseudogap observed in recent angle resolved
photoemission spectroscopy on electron-doped cuprates. In the case of the
strong-coupling mechanism, which is more relevant near half-filling, the
pseudogap can be mainly driven by short range correlations near the Mott
insulator. In the vicinity of optimal doping, where weak-coupling physics is
more relevant, large antiferromagnetic correlation lengths, seen in neutron
measurements, are the origin of the pseudogap. The t-J model is not applicable
in the latter case.
