Functional magnetic resonance imaging studies of pain: an investigation of signal decay during and across sessions.

BACKGROUND: Several investigations into brain activation caused by pain have suggested that the multiple painful stimulations used in typical block designs may cause attenuation over time of the signal within activated areas. The effect this may have on pain investigations using multiple tasks has not been investigated. The signal decay across a task of four repeating pain stimulations and between two serial pain tasks separated by a 4-min interval was examined to determine whether signal attenuation may significantly confound pain investigations.
METHODS: The characteristics of the brain activation of six subjects were determined using whole brain blood oxygenation level-dependent functional magnetic resonance imaging on a 1.5-T scanner. Tasks included both tingling and pain induced by transcutaneous electrical stimulation of the median nerve. The average group maps were analyzed by general linear modeling with corrected cluster P values of less than 0.05. The time courses of individual voxels were further investigated by analysis of variance with P values of less than 0.05.
RESULTS: Significant differences between pain and tingling were found in the ipsilateral cerebellum, contralateral thalamus, secondary somatosensory cortex, primary somatosensory cortex, and anterior cingulate cortex. Highly significant signal decay was found to exist across each single pain task, but the signal was found to be restored after a 4-min rest period.
CONCLUSIONS: This work shows that serial pain tasks can be used for functional magnetic resonance imaging studies using electrical nerve stimulation as a stimulus, as long as sufficient time is allowed between the two tasks.