  We report the phenomenon of frequency clustering in a network of
Hodgkin-Huxley neurons with spike timing-dependent plasticity. The clustering
leads to a splitting of a neural population into a few groups synchronized at
different frequencies. In this regime, the amplitude of the mean field
undergoes low-frequency modulations, which may contribute to the mechanism of
the emergence of slow oscillations of neural activity observed in spectral
power of local field potentials or electroencephalographic signals at high
frequencies. In addition to numerical simulations of such multi-clusters, we
investigate the mechanisms of the observed phenomena using the simplest case of
two clusters. In particular, we propose a phenomenological model which
describes the dynamics of two clusters taking into account the adaptation of
coupling weights. We also determine the set of plasticity functions (update
rules), which lead to multi-clustering.
