title: Functional deactivations: multiple ipsilateral brain areas engaged in the processing of somatosensory information.
abstract: Somatosensory signals modulate activity throughout a widespread network in both of the brain hemispheres: the contralateral as well as the ipsilateral side of the brain relative to the stimulated limb. To analyze the ipsilateral somatosensory brain areas that are engaged during limb stimulation, we performed functional magnetic resonance imaging (fMRI) in 12 healthy subjects during electrical median nerve stimulation using both a block- and an event-related fMRI design. Data were analyzed through the use of model-dependent (SPM) and model-independent (ICA) approaches. Beyond the well-known positive blood oxygenation level-dependent (BOLD) responses, negative deflections of the BOLD response were found consistently in several ipsilateral brain areas, including the primary somatosensory cortex, the supplementary motor area, the insula, the dorsal part of the posterior cingulate cortex, and the contralateral cerebellum. Compared to their positive counterparts, the negative hemodynamic responses showed a different time course, with an onset time delay of 2.4 s and a peak delay of 0.7 s. This characteristic delay was observed in all investigated areas and verified by a second (purely tactile) event-related paradigm, suggesting a systematic difference for brain areas involved in the processing of somatosensory information. These findings may indicate that the physiological basis of these deactivations differs from that of the positive BOLD responses. Therefore, an altered model for the negative BOLD response may be beneficial to further model-dependent fMRI analyses.
authors.affiliation: Department of Neurology, University of Jena, Germany. carsten.klingner@med.uni-jena.de
authors.forename: Carsten M
authors.initials: CM
authors.lastname: Klingner
authors.forename: Ralph
authors.initials: R
authors.lastname: Huonker
authors.forename: Sandra
authors.initials: S
authors.lastname: Flemming
authors.forename: Caroline
authors.initials: C
authors.lastname: Hasler
authors.forename: Stefan
authors.initials: S
authors.lastname: Brodoehl
authors.forename: Christoph
authors.initials: C
authors.lastname: Preul
authors.forename: Hartmut
authors.initials: H
authors.lastname: Burmeister
authors.forename: Andreas
authors.initials: A
authors.lastname: Kastrup
authors.forename: Otto W
authors.initials: OW
authors.lastname: Witte
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002531:Cerebellum / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008475:Median Nerve / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology*; D055698:Touch Perception / Q000502:physiology*