Paradoxical behavioral facilitation in response to Zolpidem in severely brain-injured subjects with disorders of consciousness is well documented, but relatively rare. Researchers in the following study have demonstrated the same low frequency waves in the EEG readings of 3 subjects, who had suffered brain damage in different ways. The investigators hypothesize that Zolpidem briefly triggers a fast wave of excitation in the brain before causing sleep - a phenomenon called Paradoxical excitation. The drug turns on a circuit-mesocircuit-which links cortical areas of the brain to the central thalamus and striatum. The thalamus is the key to consiosness and this could explain why Zolpidem briefly wakes up brain injured patients from a minimally consious state.