Sequential pain responses in the formalin test related to needle rotation. The black bar labeled "acupuncture" indicates the 5 minute time interval during which the 3 minute treatment occurred for all mice. The needle was inserted 5 minutes after pain induction. In the rotation group, the needle was rotated two times per second in the first minute after the start of pain induction and for another two times per second in the last minute of acupuncture stimulation. The non-rotation group received acupuncture for 3 minutes without needle rotation. All data are presented as mean ± SE. *p < 0.05 and **p < 0.01 when compared to the control group.