A model is developed for self-modulated pulsations in the outer trapped electron belts. The pulsations are a consequence of growth of VLF waves and removal of trapped electrons following an electron injection event. If too many electrons are removed by wave interactions, the system restores itself by building up the flux again to values exceeding the equilibrium flux, repeated through many cycles. Pulsations are shown to be po ssible for both broadband VLF wave generation and narrowband wave generation. The resulting electron orecipitation pulses are consistent with observations of pulsating aurorae on the morningside following a substorm injection event. The conditions for pulsations are quite stringent and favor trapped particle fluxes near the stable trapping limit. Individual pulses may be in or near strong diffusion.