Abstract: An apparatus for determining in vivo hyperalgesia to thermal stimulation in an unrestrained subject within a predetermined space permitting the selective application of radiant heat to a site of the subject comprises a timer, a movable light source, a light detector and a stopper for the timer, the light source and the detector, the stopper being electrically connected thereto and automatically activated by the light detector upon site withdrawal, and a starter for the timer and the light source and for activating the light detector that is electrically connected thereto. When the light source is aimed at the site and positioned at a distance effective to locally provide radiant heat thereto and the starter is activated, after a latency time period the light beam elicits a spontaneous withdrawal response from the subject that is detected by the detector.

Abstract: A method for discerning a peripherally-mediated response to thermal simulation caused by a drug in an unrestrained subject is disclosed whereby it can be determined if the drug acts substantially like the placebo. Also disclosed is a method of determining the response to thermal stimulation caused by a drug in an unrestrained subject by determining the difference between the drug withdrawal latency time period and the placebo withdrawal latency time period. Also disclosed is a method of discerning a peripheral response to thermal stimulation in an unrestrained subject by comparing the withdrawal latency time period of one site with that of a second site.