  Recent Raman experiments [F. Venturini et al., Phys. Rev. Lett. {\bf 89},
107003-1,(2002)] done in $Bi_2 Sr_2 Ca Cu_2 O_4$ have found that antinodal
quasiparticles become insulating when the doping is varied from overdoped to
optimally doped while nodal quasiparticles remain metallic. We propose a simple
explanation based on the incoherence of the spectral function in the antinodal
direction due to the strong scattering suffered by the quasiparticles in the
proximity of the Van Hove singularity.
