Functional topography of the secondary somatosensory cortex for nonpainful and painful stimuli: an fMRI study.
The regional activity of the contralateral primary (SI) and the bilateral secondary (SII) somatosensory areas during median nerve stimulations at five intensity levels (ranging from nonpainful motor threshold to moderate pain) was studied by means of functional magnetic resonance imaging (fMRI). The aim was to characterize the functional topography of SII compared to SI as a function of the stimulus intensity. Results showed that the galvanic stimulation of the median nerve activated the contralateral SI at all stimulus intensities. When considered as a single region, SII was more strongly activated in the contralateral than in the ipsilateral hemisphere. When a finer spatial analysis of the SII responses was performed, the activity for the painful stimulation was localized more posteriorly compared to that for the nonpainful stimulation. This is the first report on such a SII segregation for transient galvanic stimulations. The activity (relative signal intensity) of this posterior area increased with the increase of the stimulus intensity. These results suggest a spatial segregation of the neural populations that process signals conveyed by dorsal column-medial lemniscus (nonpainful signals) and neospinothalamic (painful signals) pathways. Further fMRI experiments should evaluate the functional properties of these two SII subregions during tasks involving sensorimotor integration, learning, and memory demands.
Ferretti
Antonio
A
Department of Clinical Sciences and Bio-imaging, University of Chieti, Italy. aferretti@itab.unich.it
Babiloni
Claudio
C
Gratta
Cosimo Del
CD
Caulo
Massimo
M
Tartaro
Armando
A
Bonomo
Lorenzo
L
Rossini
Paolo Maria
PM
Romani
Gian Luca
GL
D000328:Adult; D001931:Brain Mapping; D004558:Electric Stimulation; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008475:Median Nerve / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010146:Pain / Q000503:physiopathology*; D013003:Somatosensory Cortex / Q000503:physiopathology*
D010100:Oxygen