The Journal of Neuroscience, July 22, 2009, 29(29):9314-9320; doi:10.1523/JNEUROSCI.0400-09.2009
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Behavioral/Systems/Cognitive
Somatotopic Organization of Gentle Touch Processing in the Posterior Insular Cortex
Malin Björnsdotter,
Line Löken,
Håkan Olausson,
Åke Vallbo, and
Johan Wessberg
Institute of Neuroscience and Physiology, University of Gothenburg, 413 90 Göteborg, Sweden
Correspondence should be addressed to Malin Björnsdotter, Medicinaregatan 11, 413 90 Göteborg, Sweden. Email: malin.bjornsdotter{at}neuro.gu.se
A network of thin (C and A
) afferents relays various signals related to the physiological condition of the body, including sensations of gentle touch, pain, and temperature changes. Such afferents project to the insular cortex, where a somatotopic organization of responses to noxious and cooling stimuli was recently observed. To explore the possibility of a corresponding body-map topography in relation to gentle touch mediated through C tactile (CT) fibers, we applied soft brush stimuli to the right forearm and thigh of a patient (GL) lacking Aβ afferents, and six healthy subjects during functional magnetic resonance imaging (fMRI). For improved fMRI analysis, we used a highly sensitive multivariate voxel clustering approach. A somatotopic organization of the left (contralateral) posterior insular cortex was consistently demonstrated in all subjects, including GL, with forearm projecting anterior to thigh stimulation. Also, despite denying any sense of touch in daily life, GL correctly localized 97% of the stimuli to the forearm or thigh in a forced-choice paradigm. The consistency in activation patterns across GL and the healthy subjects suggests that the identified organization reflects the central projection of CT fibers. Moreover, substantial similarities of the presently observed insular activation with that described for noxious and cooling stimuli solidify the hypothesized sensory-affective role of the CT system in the maintenance of physical well-being as part of a thin-afferent homeostatic network.
Received Jan. 22, 2009;
revised May 18, 2009;
accepted June 20, 2009.
Correspondence should be addressed to Malin Björnsdotter, Medicinaregatan 11, 413 90 Göteborg, Sweden. Email: malin.bjornsdotter{at}neuro.gu.se
