Tension type headache more than 5 days per month during the last year.

Tension type headache on the experimental day.

Any other primary headache disorder

Migraine 48 hour before and after the experimental day (only episodic migraine patients)

Use of antimigraine medication or pain-killer on the experimental day before PET

Pregnant or breastfeeding women.

Contraindications against MRI.

History or clinical sign of cardio- or cerebrovascular disease.

Untreated severe mental disorder or drug abuse.

Other diseases or disorders interpreted, by the examining doctor, to interfere with participation in the study.

Not accepting information about potential accidental findings during the experiment.

Investigation of Serotonin Receptor Binding in the Migraine Brain Using Positron Emission Tomography