Pain processing during three levels of noxious stimulation produces differential patterns of central activity

Abstract

Previous functional imaging studies have demonstrated a number of discrete brain structures that increase activity with noxious stimulation. Of the commonly identified central structures, only the anterior cingulate cortex shows a consistent response during the experience of pain. The insula and thalamus demonstrate reasonable consistency while all other regions, including the lentiform nucleus, somatosensory cortex and prefrontal cortex, are active in no more than half the current studies. The reason for such discrepancy is likely to be due in part to methodological variability and in part to individual variability. One aspect of the methodology which is likely to contribute is the stimulus intensity. Studies vary considerably regarding the intensity of the noxious and non-noxious stimuli delivered. This is likely to produce varying activation of central structures coding for the intensity, affective and cognitive components of pain. Using twelve healthy volunteers and positron emission tomography (PET), the regional cerebral blood flow (rCBF) responses to four intensities of stimulation were recorded. The stimulation was delivered by a CO2 laser and was described subjectively as either warm (not painful), pain threshold just painful), mildly painful or moderately painful. The following group subtractions were made to examine the changing cerebral responses as the stimulus intensity increased: (1) just painful - warm; (2) mild pain - warm; and (3) moderate pain - warm. In addition, rCBF changes were correlated with the subjective stimulus ratings. The results for comparison '1' indicated activity in the contralateral prefrontal (area 10/46/44), bilateral inferior parietal (area 40) and ipsilateral premotor cortices (area 6), possibly reflecting initial orientation and plans for movement. The latter comparisons and correlation analysis indicated a wide range of active regions including bilateral prefrontal, inferior parietal and premotor cortices and thalamic responses, contralateral hippocampus, insula and primary somatosensory cortex and ipsilateral perigenual cingulate cortex (area 24) and medial frontal cortex (area 32). Decreased rCBF was observed in the amygdala region. These responses were interpreted with respect to their contribution to the multidimensional aspects of pain including fear avoidance, affect, sensation and motivation or motor initiation. It is suggested that future studies examine the precise roles of each particular region during the central processing of pain.

An fMRI study of acupuncture using independent component analysis

“…The rostal part of the ACC, which is connected to the amygdala and the periaqueductal gray matter (PAG), modulates the internal emotional response to pain [9]. The frontal gyri are consistent with activations identified in previous human experimental neuroimaging studies of pain [10]. The different functional networks indicated that the baseline changed after the needle manipulation.…”

“…The putamen is known to be crucial for motor activity [24]. The thalamus was identified in pain studies [10]. The postcentral is the SII area as well as the PHIPP, tonsil, and culmen in the cerebellum, which are involved in processing incoming sensory stimulation and high pain sensation of the subjects [10].…”

“…The thalamus was identified in pain studies [10]. The postcentral is the SII area as well as the PHIPP, tonsil, and culmen in the cerebellum, which are involved in processing incoming sensory stimulation and high pain sensation of the subjects [10]. These different activation areas of the networks were critical in the analysis regarding the 'on-state' and 'off-state.…”

Pharmacological FMRI in the development of new analgesic compounds

“…Interestingly, gabapentin also affected stimulus-induced deactivations, which suggests that the drug has substantial effects on attentional and arousal networks in the brain, in line with its sedative side effects. With respect to clinical pain, we recently confirmed the relationship between the subjective perception of pain intensity and the haemodynamic response, previously only described in healthy volunteers (53)(54)(55)(56)(57)(58). Out of several brain regions in which the magnitude of the FMRI signal encoded the perceived intensity of brush-evoked allodynic pain in neuropathic pain patients, the caudal anterior insula reflected the subjective allodynic pain ratings best (59) (Fig.…”

Effect of patellar taping on vasti onset timing, knee kinematics, and kinetics in asymptomatic individuals with a delayed onset of vastus medialis oblique

“…However, it is known that pain affects motor output in a variety of ways, ranging from changes in reflex activation to central inhibition to drive the muscle maximally. [35][36][37] We have also shown that experimentally induced knee pain via injection of hypertonic saline into the infrapatellar fat pad in healthy individuals can lead to alterations in vasti control during stair stepping, which are reversed when pain subsides (unpublished data). Thus, pain is a potent driver of changes in neuromotor control.…”