Quantitative Sensory Testing and Occipital Nerve Stimulator

Inclusion criteria Subject satisfies standard criteria in the study centre for ONS implantation and the NICE 452 criteria for intractable chronic migraine or cluster headache. Patients who have given their written informed consent. Patient is able and willing to comply with study procedures and follow up schedule. Participants will need a good understanding of the English Language and hence. This is a requirement not just for this research but also for the success of the interventions and the full understanding of QST. Patients undergoing surgery (non-painful complaint) 'dilatation and curettage' (D\&C). Exclusion criteria * Any inclusion criteria not met * Female patients of childbearing age who is or plans on becoming pregnant during the course of the study * Patients with diabetes * Patients known to have a condition that in the investigator's judgment precludes participation in the study. * Patients who have received an investigational drug or have used an investigational device in the 30 days preceding to study entry