Interactions between subregions of somatosensory cortex during nociceptive stimulation are accompanied by clinically relevant alterations of cortical responses to myelinated and unmyelinated nociceptors.
The intensity and submodality of pain are widely attributed to stimulus encoding by peripheral and subcortical spinal/trigeminal portions of the somatosensory nervous system. Consistent with this interpretation are studies of surgically anesthetized animals, demonstrating that relationships between nociceptive stimulation and activation of neurons are similar at subcortical levels of somatosensory projection and within the primary somatosensory cortex (in cytoarchitectural areas 3b and 1 of somatosensory cortex, SI). Such findings have led to characterizations of SI as a network that preserves, rather than transforms, the excitatory drive it receives from subcortical levels. Inconsistent with this perspective are images and neurophysiological recordings of SI neurons in lightly anesthetized primates. These studies demonstrate that an extreme anterior position within SI (area 3a) receives input originating predominantly from unmyelinated nociceptors, distinguishing it from posterior SI (areas 3b and 1), long recognized as receiving input predominantly from myelinated afferents, including nociceptors. Of particular importance, interactions between these subregions during maintained nociceptive stimulation are accompanied by an altered SI response to myelinated and unmyelinated nociceptors. A revised view of pain coding within SI cortex is discussed, and potentially significant clinical implications are emphasized.
aDepartment of Neuroscience, University of Florida College of Medicine, Gainesville, FL 32610-0244, USA
bDepartment of Physiology, University of North Carolina School of Medicine, Chapel Hill, NC, USA
cDepartment of Computer Sciences, University of North Carolina School of Medicine, Chapel Hill, NC, USA
dSenior School, Shadyside Academy, Pittsburgh, PA, USA
*Corresponding author. Tel.: +1 352 275 4123; fax: +1 352 371 2378.
Submitted November 17, 2011; revised September 15, 2012; accepted October 29, 2012.