title: Effects of age on negative BOLD signal changes in the primary somatosensory cortex.
abstract: In addition to a contralateral activation of the primary and secondary somatosensory cortices, peripheral sensory stimulation has been shown to elicit responses in the ipsilateral primary somatosensory cortex (SI). In particular, evidence is accumulating that processes of interhemispheric inhibition as depicted by negative blood oxygenation level dependent (BOLD) signal changes are part of somatosensory processes. The aim of the study was to analyze age-related differences in patterns of cerebral activation in the somatosensory system in general and processes of interhemispheric inhibition in particular. For this, a functional magnetic resonance imaging (fMRI) study was performed including 14 younger (mean age 23.3±0.9years) and 13 healthy older participants (mean age 73.2±8.3years). All subjects were scanned during peripheral electrical median nerve stimulation (40Hz) to obtain BOLD responses in the somatosensory system. Moreover, the individual current perception threshold (CPT) as a quantitative measure of sensory function was determined in a separate psychophysical testing. Significant increases in BOLD signal across the entire group could be measured within the contralateral SI, in the bilateral secondary somatosensory cortex (SII), the contralateral supplementary motor area and the insula. Negative BOLD signal changes were delineated in ipsilateral SI/MI as well as in the ipsilateral thalamus and basal ganglia. After comparing the two groups, only the cortical deactivation in ipsilateral SI in the early stimulation phase as well as the activation in contralateral SI and SII in the late stimulation block remained as statistically significant differences between the two groups. The psychophysical experiments yielded a significant age-dependent effect of CPT change with less difference in the older group which is in line with the significantly smaller alterations in maximal BOLD signal change in the contra- and ipsilateral SI found between the two groups. Healthy aging seems to be associated with a decrease in intracerebral inhibition as reflected by smaller negative BOLD signal changes during fMRI tasks. This finding could constitute an important link between age-related neurophysiological changes and behavioral alterations in humans.
authors.affiliation: Department of Neurology, University of Göttingen, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Gröschel
authors.forename: Jan Martin
authors.initials: JM
authors.lastname: Sohns
authors.forename: Carsten
authors.initials: C
authors.lastname: Schmidt-Samoa
authors.forename: Jürgen
authors.initials: J
authors.lastname: Baudewig
authors.forename: Lars
authors.initials: L
authors.lastname: Becker
authors.forename: Peter
authors.initials: P
authors.lastname: Dechent
authors.forename: Andreas
authors.initials: A
authors.lastname: Kastrup
mesh_terms: D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D001931:Brain Mapping; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D013003:Somatosensory Cortex / Q000502:physiology*; D055815:Young Adult