In the imaging session, fMRI and structural data will be acquired for the steady-state resting scan run (REST), event-related block design bothersomeness and emotion stimuli model scan run (TASK 1), structural image acquisition using three-dimensional T1-weighted turbo field echo (3D-T1W), event-related block design bothersomeness and emotion stimuli model scan run (TASK 2), diffusion tensor imaging (DTI), and the steady-state LBE pain-model scan run (TASK 3)
Both TASK 1 and 2 will consist of a block design with 20 6-s bothersomeness and emotion stimulation blocks, which will be followed by 9-s inter-stimulus interval (ISI) blocks in order to prevent anticipation during the measurements. The 20 stimuli of bothersomeness and emotion will be comprised of five types of stimuli (bothersomeness only, emotion (neutral) only, emotion (negative) only, bothersomeness and emotion (neutral), bothersomeness and emotion (negative)) and arranged in pseudo-random order. Bothersome stimuli will be delivered with the Stimuplex® HNS 12 electrical stimulator onto the low back of the ipsilateral side of the sciatica using the StiMus® surface electrode (HUREV Co., Ltd., Gangwon-do, Korea). Emotions will be elicited by utilizing stimuli from the standardized International Affective Picture System (IAPS) [
39,
40], which has been frequently used in neuroimaging studies. IAPS pictures with human content will be used in the present study. Table
1 presents the reported valence and arousal of the 16 negative and 16 neutral IAPS pictures used. We selected pictures that have low differences in valence and arousal between sexes when there is often quite a difference according to gender in the IAPS pictures. The images will be projected through a goggle onto a screen in the MRI scanner. During the ISI and bothersome stimuli alone, a black screen will be displayed. The IAPS pictures will be shown for 6 s and in the combination of picture and bothersome stimuli, the bothersome stimulus will be delivered 3 s after the onset of the picture, based on studies on startle responses and physiological response times for emotional stimuli [
41,
42].
In TASK 3, the LBE model of endogenous LBP will be applied for the steady-state pain scan run. By inflating a cuff bladder made of rubber under the most painful area of the lower back, the extension angle of the lower back increases to induce pain. The cuff inflator (located in the control room) will be connected to the cuff bladder through a rubber tube so that the applied air pressure to the cuff bladder can be controlled according to patient response by manual operation outside the scanner.