• Meng Liang, André Mouraux, and Gian Domenico Iannetti.
• Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, United Kingdom.
• J. Neurosci. 2011 Jun 15;31(24):8976-85.

AbstractSeveral studies have suggested that, in higher primates, nociceptive somatosensory information is processed in parallel in the primary (S1) and secondary (S2) somatosensory cortices, whereas non-nociceptive somatosensory input is processed serially from S1 to S2. However, evidence suggesting that both nociceptive and non-nociceptive somatosensory inputs are processed in parallel in S1 and S2 also exists. Here, we aimed to clarify whether or not the hierarchical organization of nociceptive and non-nociceptive somatosensory processing in S1 and S2 differs in humans. To address this question, we applied dynamic causal modeling and Bayesian model selection to functional magnetic resonance imaging (fMRI) data collected during the selective stimulation of nociceptive and non-nociceptive somatosensory afferents in humans. This novel approach allowed us to explore how nociceptive and non-nociceptive somatosensory information flows within the somatosensory system. We found that the neural activities elicited by both nociceptive and non-nociceptive somatosensory stimuli are best explained by models in which the fMRI responses in both S1 and S2 depend on direct thalamocortical projections. These observations indicate that, in humans, both nociceptive and non-nociceptive information are processed in parallel in S1 and S2.

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