  We investigate theoretically and experimentally the optical beam propagation
in the nematic liquid crystal with negative dielectric anisotropy, which is
aligned homeotropically in a $80\mu m$-thickness planar cell in the presence of
an externally voltage. It is predicted that the nonlocal nonlinearity of liquid
crystal undergo an oscillatory response function with a negative nonlinear
refractive index coefficient. We found that the oscillatory nonlocal
nonlinearity can support stable bright solitons, which are observed in
experiment. We also found that abnormal modulation instability occurs with
infinity gain coefficient at a fixed spatial frequency, which is no depend on
the beam intensity. We observed the modulation instability in the liquid
crystal at a very low intensity ($0.26W/cm^2$), and the maximum gain frequency
were found kept unchange when beam power changes over 2-3 orders of magnitude.
