Haemodynamic brain responses to acute pain in humans

Abstract

Turning attention towards or away from a painful heat stimulus is known to modify both the subjective intensity of pain and the cortical evoked potentials to noxious stimuli. Using PET, we investigated in 12 volunteers whether pain-related regional cerebral blood flow (rCBF) changes were also modulated by attention. High (mean 46.6 degrees C) or low (mean 39 degrees C) intensity thermal stimuli were applied to the hand under three attentional conditions: (i) attention directed towards the stimuli, (ii) attention diverted from the stimuli, and (iii) no task. Only the insular/second somatosensory cortices were found to respond whatever the attentional context and might, therefore, subserve the sensory-discriminative dimension of pain (intensity coding). In parallel, other rCBF changes previously described as 'pain-related' appeared to depend essentially on the attentional context. Attention to the thermal stimulus involved a large network which was primarily right-sided, including prefrontal, posterior parietal, anterior cingulate cortices and thalamus. Anterior cingulate activity was not found to pertain to the intensity coding network but rather to the attentional neural activity triggered by pain. The attentional network disclosed in this study could be further subdivided into a non-specific arousal component, involving thalamic and upper brainstem regions, and a selective attention and orientating component including prefrontal, posterior parietal and cingulate cortices. A further effect observed in response to high intensity stimuli was a rCBF decrease within the somatosensory cortex ipsilateral to stimulation, which was considered to reflect contrast enhancing and/or anticipation processes. Attentional processes could possibly explain part of the variability observed in previous PET reports and should therefore be considered in further studies on pain in both normal subjects and patients with chronic pain.

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.…”

Using fMRI to Quantify the Time Dependence of Remifentanil Analgesia in the Human Brain

“…Furthermore, the posterior insula has recently been implicated as a thermosensory cortex (Craig et al, 2000). Peyron et al (1999) suggested the role of insula in the sensory discriminative dimension of pain intensity encoding. PET ligand binding studies have shown the insula to posses a high concentration of m-opioid receptors (Jones et al, 1991b, c), suggesting the insula as a potential site of analgesic action for remifentanil, a m-opioid agonist.…”

Anxiety in healthy humans is associated with orbital frontal chemistry

“…It is also possible that the cingulate is not a specific area for anxiety since multiple cognitive tasks activate this region, including tasks targeting attention, affect and pain. [30][31][32][33] The cingulate cortex may be involved in more general non-specific attentional states, including a readiness to escape from a threatening situation. The role of OFC may be more specifically linked to anxiety since this area of the brain is involved in decision-making behavior, including ambiguous situations of personal threat.…”