TRAUMATIC NOCICEPTIVE PAIN ACTIVATES THE HYPOTHALAMUS AND THE PERIAQUEDUCTAL GRAY - A POSITRON EMISSION TOMOGRAPHY STUDY

The study was conducted to investigate which areas of the brain respon d to a painful encounter of minor dermal injury (a model of clinical p ain) elicited by intracutaneous injection of a minute amount of ethano l. Four healthy volunteers (27-46 years) were subjected to positron em ission tomographic (PET) investigation of regional cerebral blood flow (rCBF), using [O-15]butanol as tracer. The ethanol (20 mu l, 70%) and saline (20 mu l, 0.9%) were injected intracutaneously 3 times in a si ngle-blinded, semi-randomised manner for the pain experiment. All the injections were performed, adjacent to each other, at the lateral aspe ct of the right upper arm. Subjective sensory intensity of pain, unple asantness and anxiety were rated with separate 100-mm visual analogue scales together with the Spielberger's State Anxiety Inventory (Spielb erger et al. 1970) and heart rate. Paired-subtraction (pixel-by-pixel) between ethanol and saline was performed. Traumatic pain significantl y caused higher ratings of intensity and affect scales, i.e., pain int ensity, unpleasantness and increased sympathetic activity (evidenced b y tachycardia). In contrast the anxiety rating remained unchanged. Acu te traumatic nociceptive pain prominently activated the hypothalamus a nd periaqueductal gray (FAG). In addition, activations of the prefront al cortex (PFC), insular, anterior cingulate cortex (ACC); posterior p arietal cortex (PPC), primary motor/somatosensory areas (MI/SI: face, upper arm), supplementary motor area (SMA), and cerebellum were also d emonstrated, The central processing of the pain-relevant/anticipatory arousal also engaged the FAG. This study demonstrates the involvement of the human cerebral cortex in perception, arousal, cognitive evaluat ive processes, and, hence, affective reactions (somatic/autonomic outf low) associated with pain. The pain stimulus of traumatic character ma y, by its very nature, evoke the central processing to involve both th e hypothalamus and the FAG.