Influences of Anxiety and Fear on Conditioned Pain Modulationin Healthy Individuals and Pain Patients

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The term Conditioned Pain Modulation (CPM) describes the 'pain inhibits pain' phenomenon, which represents a supra-spinal loop effect, with upper centres in the brain stem. It is part of the descending inhibitory control system, which has first been described at a pure physiological level as Diffuse Noxious Inhibitory Controls (DNIC). CPM testing has become very popular because changes in CPM have promised to underlie sex and age differences in pain processing and, even more importantly, seem to belong to the factors contributing to the development of chronic pain as well as to the factors predicting treatment efficacy. Thus, CPM has become a marker for the inhibitory pain processing capacity. With very few exceptions the functional relation of this emerging marker of pain inhibition with higher-order subcortical and cortical networks and psychological influences on CPM effects have yet been neglected although higher-order influences on descending pain inhibitory systems in general have been acknowledged for a long time. To change this situation and start with psychologically critical variables for pain processing, the influences of anxiety (anticipation of threat) and fear (confrontation with threat) as well as of internal (associated with noxious stimulation) and external threat (independent of noxious stimulation) will be investigated. The choice of these factors has been driven by definite knowledge of their efficiency in acting on pain processing in general. The research question here is whether these factors exert their influence on pain via modulation of CPM. Besides healthy control subjects, patients with chronic musculoskeletal pain will be investigated because in these patients the affective influences on CPM are assumed to be more pronounced and potentially of pathogenetic relevance. Due to presumed similarities in pathophysiology (central sensitization) but difference in pain severity (intensity and spread) and psychological accompaniments, patients with fibromyalgia and chronic tension-type headache (CTTH) will be studied as clinical models.