Phantom headache: pain-memory-emotion hypothesis for chronic daily headache?

The neurobiology of chronic pain, including chronic daily headache (CDH) is not completely understood. "Pain memory" hypothesis is one of the mechanisms for phantom limb pain. We reviewed the literature to delineate a relation of "pain memory" for the development of CDH. There is a direct relation of pain to memory. Patients with poor memory have less chance to develop "pain memory", hence less possibility to develop chronic pain. Progressive memory impairment may lead to decline in headache prevalence. A similar relation of pain is also noted with emotional or psychiatric symptoms. Literature review suggests that there is marked overlap in the neural network of pain to that of memory and emotions. We speculate that pain, memory, and emotions are interrelated in triangular pattern, and each of these three is related to other two in bidirectional pattern, i.e., stimulation of one of these will stimulate other symptoms/networks and vice versa (triangular theory for chronic pain). Longstanding or recurrent noxious stimuli will strengthen this interrelation, and this may be responsible for chronicity of pain. Reduction of both chronic pain and psychological symptoms by cognitive behavioral therapy or psychological interventions further suggests a bidirectional interrelation between pain and emotion. Longitudinal studies are warranted on the prevalence of headache and other painful conditions in patients with progressive memory impairment to delineate the relation of pain to memory. Interrelation of headache to emotional symptoms should also be explored.