Brain dynamics for perception of tactile allodynia (touch-induced pain) in postherpetic neuralgia

Abstract

Postherpetic neuralgia (PHN) is a debilitating chronic pain condition often accompanied by a sensation of pain when the affected region is touched (tactile allodynia). Here we identify brain regions involved in stimulus-induced touch-evoked pain (dynamical mechanical allodynia, DMA), compare brain activity between DMA and spontaneous pain (described earlier for the same patients in [28], delineate regions that specifically code the magnitude of perceived allodynia, and show the transformation of allodynia-related information in the brain as a time-evolving network. Eleven PHN patients were studied for DMA and its modulation with Lidoderm therapy (patches of 5% lidocaine applied to the PHN affected body part). Continuous ratings of pain while the affected body part was brushed during fMRI were contrasted with non-painful touch when brushing was applied to an equivalent opposite body site, and with fluctuations of a bar observed during scanning, at three sessions relative to Lidoderm treatment. Lidoderm treatment did not decrease DMA ratings but did decrease spontaneous pain. Multiple brain areas showed preferential activity for allodynia. However, mainly responses in the bilateral putamen and left medial temporal gyrus were related to the magnitude of allodynia. Both DMA and spontaneous pain perceptions were best represented within the same sub-cortical structures but with minimal overlap, implying that PHN pain modulates behavioral learning and hedonics. These results have important clinical implications regarding adequate therapy.

Chronic pain: The role of learning and brain plasticity

“…These results, together with our fMRI studies in other chronic pain conditions (Baliki et al, 2008; Baliki et al, 2005; Farmer et al, 2011; Geha et al, 2007; Geha, Baliki, Wang, et al, 2008) and our additional brain morphometry studies (Baliki, Schnitzer, et al, 2011; Geha, Baliki, Harden, et al, 2008), have prompted the proposal of a new mechanistic model for the transition to pain chronicity. This model was proposed and expounded in three review articles (Apkarian, 2008; Apkarian et al, 2009; Apkarian et al, 2011).…”

Extended cortical activations during evaluating successive pain stimuli

“…Decision making under uncertainty has also been assigned to the inferior parietal lobule (Vickery and Jiang, 2009). With respect to pain, activation of the middle temporal gyrus was related to the amount of tactile allodynia in postherpetic neuralgia (Geha et al, 2008).…”

Neuroimaging as a Tool for Pain Diagnosis and Analgesic Development

“…The evoked pain results in similar brain activation as the acute pain in healthy controls. [43][44][45] Tonic clinical pain results in a different brain activity pattern than evoked clinical pain; for example, dynamic mechanical allodynia in patients with post-herpetic neuralgia results in different activation patterns than the ongoing pain. 43,46 Also the evoked pain differs from the ongoing, tonic pain in patients with arthritis.…”

“…[43][44][45] Tonic clinical pain results in a different brain activity pattern than evoked clinical pain; for example, dynamic mechanical allodynia in patients with post-herpetic neuralgia results in different activation patterns than the ongoing pain. 43,46 Also the evoked pain differs from the ongoing, tonic pain in patients with arthritis. 44 This observation is very important for treatment development, as it highlights the fact that the evoked pain typically used in pain studies, even though it is disease-related, is not the same as the ongoing pain the patients experience during the course of their disease, and often describe as their most problematic symptom.…”