Psychophysical methods for improved observation of nociceptive processing

Abstract

The malfunctioning of the nociceptive system may contribute to post-surgical chronic pain development. Psychophysical methods are used to observe nociceptive stimulus processing and sensory function by the estimation of a pain threshold. With these methods, it is possible to identify nociceptive disease. It remains, however, difficult to obtain information about individual contributions of underlying mechanisms to stimulus processing. Furthermore, a single thresholds estimate cannot be used to observe changes in the threshold as a result of changes in the nociceptive system. By presenting stimuli with various temporal stimulus properties (e.g., pulse-width, number of pulses, or inter-pulse interval) and estimating corresponding thresholds, the individual contributions of peripheral and central nociceptive processes to stimulus processing might be distinguished. Moreover, tracking these thresholds over time might help observing changes in the nociceptive system. Combined, this could contribute to an improved observation of nociceptive processing. The primary objective of the work presented in this thesis is to develop a tool allowing the simultaneous observation of individual contributions of nociceptive mechanisms to sensory processing. Two goals are identified in order to achieve the primary objective: 1) develop experimental techniques allowing the simultaneous observation of multiple non-stationary psychophysical thresholds, and 2) characterize the contributions of nociceptive mechanisms to sensory processing. The research presented in this thesis provides psychophysical methods for improved observation of nociceptive processing. With the developed methods, it is possible to simultaneously observe the contributions of various nociceptive processes. Based on the results described in this thesis, several recommendations are provided for setting up and performing relatively short psychophysical experiments. An experiment lasting for about 30 minutes can contribute to observation of peripheral and central processes, as well as the effect of a conditioning stimulus on these processes. The duration can be shortened to about 10 minutes when the effect of a conditioning stimulus is irrelevant.