<b>Change of prefrontal cortex blood flow </b><b>during pain stimulation </b>

Abstract

The prefrontal cortex (PFC) is widely associated with cognitive and emotional functions,including attention, decision making, goal-directed behavior, and working memory. In a previous study, neural activity and morphological alterations in PFC were detected in patients with chronic pain. In addition, these patients had impaired performance on emotional decision-making tests and increased incidence of depressive and anxiety disorders. However, little is known about the time course of PFC blood flow during pain stimulation. Therefore, we examined the time course of PFC blood flow and the relationship between PFC activation and the subjective pain score during thermal stimuli. Fifteen healthy right-handed subjects participated in this study. Thermal stimuli were delivered to right dorsal forearm for 30 sec by a 5 × 5-mm peltier device (Unique Medical, Japan; UDH-300). Pain intensity was assessed using a visual analog scale (VAS) after the stimuli were delivered, and PFC blood flow data were obtained using near-infrared spectroscopy. The oxyhemoglobin (oxyHb) waveform was divided into four segments: the “baseline" segment for 10 s before the task period, the “first" segment for 10 s from the task period, the “middle"segment for 10 s from the end of the first segment, and the “last" segment of 10 s from the end of the middle segment. OxyHb data were averaged across the four segments and analyzed using Tukey's post hoc test. We calculated Spearman's correlation coefficient between the pain VAS score and oxyHb in each segment (first, middle, and last) during thermal stimuli.In addition, high-sensitivity (5 subjects) and low-sensitivity (5 subjects) groups were divided using the VAS score, and the differences in average oxyHb in each segment (first, middle, and last) between the high- and low-sensitivity groups were assessed using the Mann-Whitney U test.Statistically significant differences were expressed as p values less than 0.05. Furthermore, oxyHb of the last segment in the left dorsolateral PFC significantly decreased compared with those of the baseline and first segments. OxyHb of the first segment in the left side PFC decreased significantly in the high-sensitivity groups (mean VAS rating = 72.2 ± 5.6) compared with the low-sensitivity groups (mean VAS rating = 25.8 ± 8). Decrease in PFC blood flow during pain stimulation may induce atrophy and change in neural activation in PFCs of patients with chronic pain.