Table 2.

Definitions of OA and BOLD signal parameters.

Parameters	Definition
VASMax T2	Maximum VAS value during T2 of OA blocks
VASMin T3	Minimum VAS value during the first 10 s of T3 of OA blocks
ΔOA	VASMax T2 − VASMin T3, magnitude of OA in VAS
%ΔOA	(ΔOA/VASMax T2) × 100%, standardized value of ΔOA
BOLDOA	An average BOLD signal during the middle 10 s of T3 of OA block
BOLDCon	An average BOLD signal during the Constant block corresponding to BOLDOA
ΔBOLD	BOLDOA − BOLDCon

OA: offset analgesia; BOLD: blood oxygenation level-dependent; VAS: visual analog scale; T2: a 5-s 47°C stimulus during an OA block; T3: a 20-s 46°C stimulus during an OA block; Con: a Constant block.