The study of the interaction between psychological state and gastrointestinal function is complex. It is known that anxiety is one of the factors affecting visceral sensitivity in humans. The investigators speculate that visceral hypersensitivity plays an important role in symptom perception in refractory GERD. This is suggested by the reflux parameters that are usual within the physiological range during PPI therapy. The investigators previously demonstrated that refractory GERD patients have increased visceral sensitivity for thermal, chemical and mechanical esophageal stimulation compared to healthy subjects.