Middle and Long Latency Auditory Evoked Potentials and Their Usage in Fibromyalgia and Schizophrenia

1.1 Middle and long latency auditory evoked potentials and their usage in fibromyalgia FM is a chronic syndrome that occurs predominantly in women and is marked by generalized pain, multiple defined tender points, fatigue, disturbed sleep, cognitive difficulty, and numerous other somatic complaints. The etiology and pathophysiology of FM remain unclear. Despite extensive research, no structural pathology has been identified in muscles or other tissues. The general and widespread nature of pain in FM strongly suggests the involvement of central mechanisms (Williams et al., 2006). Although psychological factors associated with chronic distress appear to be important for the development of FM in many patients, abundant evidence now indicates that pain in FM reflects abnormal pain processing in the central nervous system (ie. central sensitivity) (Herrero JF et al., 2000, Staud R. et al, 2001). Recent research suggested that FM patients might have deficiencies in central inhibitory mechanisms, such as diffuse noxious inhibitory control or the endogenous pain inhibitory system. Nevertheless, little is yet known about the brain mechanisms involved in the processing of nonpainful somatosensory information in FM (Monyoto P et al., 2006, Julien N. Et al., 2005). Central mechanisms related to pathophysiology and hypervigilance have long been discussed for fibromyalgia. Nevertheless, research into this issue has been inconclusive so far. Our aim to design this study (Turker et al., 2008) was to determine whether central mechanisms played an important role in fibromyalgia via examining brain activity elicited by auditory evoked potentials in patients with FM and to assess relationship with clinical variables. Middle latency evoked potentials (Middle Latency Auditory Evoked Potentials) are composed of several components that can be recorded from 10 to 50 msec after stimulus onset. The most stable components are Na and Pa, with latencies between 16-30 msec and 30-45 msec, respectively. Most of the MLAEP complex is thought to originate near the auditory cortex, although No, Po and Na may be generated by subcortical structures.