  We searched for quasi-periodicities on year-like timescales in the light
curves of 6 blazars in the optical - near infrared bands and we made a
comparison with the high energy emission. We obtained optical/NIR light curves
from REM photometry plus archival SMARTS data and we accessed the Fermi light
curves for the $\gamma$-ray data. The periodograms often show strong peaks in
the optical and gamma-ray bands, which in some cases may be inter-related. The
significance of the revealed peaks is then discussed, taking into account that
the noise is frequency dependent. Quasi-periodicities on a year-like timescale
appear to occur often in blazars. No straightforward model describing these
possible periodicities is yet available, but some plausible interpretations for
the physical mechanisms causing periodic variabilities of these sources are
examined.
