  The effect of a high-frequency signal on the FitzHugh-Nagumo excitable model
is analyzed. We show that the firing rate is diminished as the ratio of the
high-frequency amplitude to its frequency is increased. Moreover, it is
demonstrated that the excitable character of the system, and consequently the
firing activity, is suppressed for ratios above a given threshold value. In
addition, we show that the vibrational resonance phenomenon turns up for
sufficiently large noise strength values.
