Brain activity and connectivity attributable to nociceptive signal block

Abstract

Converging lines of evidence indicate that the pain experience emerges from distributed cortical nodes that share nociceptive information. While the theory of a single pain center is still not falsifiable by current neuroimaging technology, the validation of distinct brain mechanisms for acute pain and its relief is ongoing and strongly dependent on the employed experimental design. In the current study including a total of 28 subjects, a recently presented, innovative experimental approach was adopted that is able to clearly differentiate painful from non-pain perceptions without changing stimulus strength and while recording brain activity using functional magnetic resonance imaging (fMRI). Namely, we applied a repetitive and purely nociceptive stimulus to the tooth pulp with subsequent suppression of the nociceptive barrage via a regional nerve block. The study aims were 1) to replicate previous findings of acute pain demonstrating a fundamental role of the operculo-insular region and 2) to explore its functional connectivity during pain and subsequent relief. The brain activity reduction in the posterior insula (pINS) due to pain extinction was confirmed. In addition, the posterior S2 region (OP1) showed a similar activity pattern, thus confirming the relevance of the operculo-insular cortex in acute pain processing. Furthermore, the functional connectivity analysis yielded an enhanced positive coupling of the pINS with the cerebellar culmen during pain relief, whereas the OP1 demonstrated a positive coupling with the posterior midcingulate cortex during pain. The current results support the conceptual synthesis of localized specialization of pain processing with interactions across distributed neural targets.