|Ph.D Student||Nir Rony-Reuven|
|Subject||Psychophysics and Neurophysiology of Human Pain|
Modulation: From the Physical to the Cognitive
|Department||Department of Medicine||Supervisors||Professor David Yarnitsky|
|Dr. Michal Granot|
|Full Thesis text|
The complex and multifaceted experience of pain is not the direct product of the intensity of the noxious (injurious or potentially injurious) stimulation alone. Rather, it is influenced by a number of modulatory processes expressed at the spatiotemporal and frequency domains, affected by both physical and cognitive factors. The current dissertation presents the results of two lines of investigation; the first focused on cerebral analytic processes induced by ascending nociceptive neural barrages. This was explored through objective quantitative measures of brain loci activation magnitudes as well as their activation temporal profiles and frequency content. The second line of investigation concentrated on the emanating modulation processes activated in response to ascending pain. This was investigated by subjective assessment of endogenous analgesia (EA) magnitudes in response to manipulating relevant physical and cognitive factors. The findings of the first constituent of this work suggest that greater individual intensity coding is associated with (i) augmented activation magnitudes of the primary somatosensory cortex (SI) on the spatiotemporal domain; and (ii) increased peak alpha frequencies as well as decreased alpha-1 power on the frequency domain. Importantly, frequency domain measures analyzed during resting-state were also associated with pain scores reported during the noxious condition. These psychophysical-neurophysiological relations attest to the novel properties of cortical objective measures of subjective pain perception. Furthermore, resting-state parameters might hold inherent pain modulation attributes, possibly enabling the prediction of individual responsiveness to experimental pain. The results of the second constituent address EA expression measured via the conditioning pain modulation (CPM) paradigm, focusing on the effects of physical and cognitive interventions on the conditioning stimulation, and, in turn, on CPM responses. Exploring the physical factors revealed that once a CPM response is evoked by a required conditioning pain experience, its magnitude is not further affected by increasing conditioning pain. This may suggest that CPM responses represent a saturable phenomenon. A consequent experiment, in which the perceived conditioning pain was cognitively manipulated while its intensity was kept constant, revealed that CPM-derived pain inhibition depended on the perceived pain of the conditioning stimulation rather than its physical intensity. Moreover, cognitively decreasing the perceived conditioning pain attenuated CPM magnitudes, although a ceiling effect may limit CPM enhancement following a cognitively increased conditioning pain.