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. 2018 Mar 28;14:1744806918767512. doi: 10.1177/1744806918767512

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© The Author(s) 2018

Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage).

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Figure 1. — Offset analgesia paradigm during fMRI. Three kinds of noxious thermal pain stimulus blocks were designed with the baseline fixed at 32°C, each kind of stimuli given three times in a pseudorandom order. The starting time of each block was precisely controlled by TTL (transistor-transistor logic) output for triggering thermal stimulator synchronized with fMRI scanner. The ramp rates of stimulation temperature were +26°C/s (increase) and −6°C/s (decrease). (1) Offset analgesia (OA): a total of 30-s stimuli consisted of a series of 5-s 46°C, 5-s 47°C, and 20-s 46°C stimuli; (2) Constant: a total of 30-s 46°C stimulus; (3) Short: a total of 10-s stimuli consisted of 5-s 46°C, 5-s 47°C stimuli only. One additional Constant block (shown in dotted line) was given at the beginning of the stimulation session.

fMRI: functional magnetic resonance imaging.