title: Intra- and inter-hemispheric effective connectivity in the human somatosensory cortex during pressure stimulation.
abstract: BACKGROUND
  Slow-adapting type I (SA-I) afferents deliver sensory signals to the somatosensory cortex during low-frequency (or static) mechanical stimulation. It has been reported that the somatosensory projection from SA-I afferents is effective and reliable for object grasping and manipulation. Despite a large number of neuroimaging studies on cortical activation responding to tactile stimuli mediated by SA-I afferents, how sensory information of such tactile stimuli flows over the somatosensory cortex remains poorly understood. In this study, we investigated tactile information processing of pressure stimuli between the primary (SI) and secondary (SII) somatosensory cortices by measuring effective connectivity using dynamic causal modeling (DCM). We applied pressure stimuli for 3 s to the right index fingertip of healthy participants and acquired functional magnetic resonance imaging (fMRI) data using a 3T MRI system.
  
  
  RESULTS
  DCM analysis revealed intra-hemispheric effective connectivity between the contralateral SI (cSI) and SII (cSII) characterized by both parallel (signal inputs to both cSI and cSII) and serial (signal transmission from cSI to cSII) pathways during pressure stimulation. DCM analysis also revealed inter-hemispheric effective connectivity among cSI, cSII, and the ipsilateral SII (iSII) characterized by serial (from cSI to cSII) and SII-level (from cSII to iSII) pathways during pressure stimulation.
  
  
  CONCLUSIONS
  Our results support a hierarchical somatosensory network that underlies processing of low-frequency tactile information. The network consists of parallel inputs to both cSI and cSII (intra-hemispheric), followed by serial pathways from cSI to cSII (intra-hemispheric) and from cSII to iSII (inter-hemispheric). Importantly, our results suggest that both serial and parallel processing take place in tactile information processing of static mechanical stimuli as well as highlighting the contribution of callosal transfer to bilateral neuronal interactions in SII.
authors.forename: Yoon Gi
authors.initials: YG
authors.lastname: Chung
authors.forename: Sang Woo
authors.initials: SW
authors.lastname: Han
authors.forename: Hyung-Sik
authors.initials: HS
authors.lastname: Kim
authors.forename: Soon-Cheol
authors.initials: SC
authors.lastname: Chung
authors.forename: Jang-Yeon
authors.initials: JY
authors.lastname: Park
authors.affiliation: Department of Brain and Cognitive Engineering, Korea University, Seoul, Republic of Korea. wallraven@korea.ac.kr.
authors.forename: Christian
authors.initials: C
authors.lastname: Wallraven
authors.forename: Sung-Phil
authors.initials: SP
authors.lastname: Kim
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D063132:Connectome / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D010812:Physical Stimulation / Q000379:methods*; D011312:Pressure; D013003:Somatosensory Cortex / Q000502:physiology*; D014110:Touch / Q000502:physiology*