title: Stimulus-rate sensitivity discerns area 3b of the human primary somatosensory cortex.
abstract: Previous studies have shown that the hemodynamic response of the primary somatosensory cortex (SI) to electrical median nerve stimulation doubles in strength when the stimulus rate (SR) increases from 1 to 5 Hz. Here we investigated whether such sensitivity to SR is homogenous within the functionally different subareas of the SI cortex, and whether SR sensitivity would help discern area 3b among the other SI subareas. We acquired 3-tesla functional magnetic resonance imaging (fMRI) data from nine healthy adults who received pneumotactile stimuli in 25-s blocks to three right-hand fingers, either at 1, 4, or 10 Hz. The main contrast (all stimulations pooled vs. baseline), applied to the whole brain, first limited the search to the whole SI cortex. The conjunction of SR-sensitive contrasts [4 Hz - 1 Hz] > 0 and [10 Hz - 1 Hz] > 0 ([4 Hz - 1 Hz] + [10 Hz - 1 Hz] > 0), applied to the SI cluster, then revealed an anterior-ventral subcluster that reacted more strongly to both 10-Hz and 4-Hz stimuli than to the 1-Hz stimuli. No other SR-sensitive clusters were found at the group-level in the whole-brain analysis. The site of the SR-sensitive SI subcluster corresponds to the canonical position of area 3b; such differentiation was also possible at the individual level in 5 out of 9 subjects. Thus the SR sensitivity of the BOLD response appears to discern area 3b among other subareas of the human SI cortex.
authors.affiliation: Brain Research Unit, Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, 00076 AALTO, Espoo, Finland; Advanced Magnetic Imaging Centre, Aalto NeuroImaging, Aalto University School of Science, 00076 AALTO, Espoo, Finland.
authors.forename: Yevhen
authors.initials: Y
authors.lastname: Hlushchuk
authors.affiliation: Brain Research Unit, Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, 00076 AALTO, Espoo, Finland.
authors.forename: Cristina
authors.initials: C
authors.lastname: Simões-Franklin
authors.affiliation: Brain Research Unit, Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, 00076 AALTO, Espoo, Finland; Advanced Magnetic Imaging Centre, Aalto NeuroImaging, Aalto University School of Science, 00076 AALTO, Espoo, Finland.
authors.forename: Cathy
authors.initials: C
authors.lastname: Nangini
authors.affiliation: Brain Research Unit, Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, 00076 AALTO, Espoo, Finland; Advanced Magnetic Imaging Centre, Aalto NeuroImaging, Aalto University School of Science, 00076 AALTO, Espoo, Finland.
authors.forename: Riitta
authors.initials: R
authors.lastname: Hari
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011859:Radiography; D013003:Somatosensory Cortex / Q000000981:diagnostic imaging* / Q000502:physiology*; D055698:Touch Perception / Q000502:physiology*