  The collective dynamics of excitatory pulse coupled neurons with spike timing
dependent plasticity (STDP) is studied. The introduction of STDP induces
persistent irregular oscillations between strongly and weakly synchronized
states, reminiscent of brain activity during slow-wave sleep. We explain the
oscillations by a mechanism, the Sisyphus Effect, caused by a continuous
feedback between the synaptic adjustments and the coherence in the neural
firing. Due to this effect, the synaptic weights have oscillating equilibrium
values, and this prevents the system from relaxing into a stationary
macroscopic state.
