Enduring representational plasticity after somatosensory stimulation.
Wu CW, van Gelderen P, Hanakawa T, Yaseen Z, Cohen LG.
Laboratory of Functional and Molecular Imaging, Human Cortical Physiology Section, NINDS, NIH, Bethesda, MD 20892, USA. wuwh@ninds.nih.gov
Somatosensory stimulation (SS), leading to increases in motor cortical excitability,
influences motor performance in patients with brain lesions like stroke. The
mechanisms by which SS modulates motor function are incompletely understood.
Here, we used functional magnetic resonance imaging
(fMRI, blood-oxygenation-level-dependent (BOLD), and perfusion imagings
simultaneously acquired in a 3 T magnet) to assess the effects of SS on
thumb-movement-related activation in three regions of interest (ROI) in
the motor network: primary motor cortex (M1), primary somatosensory
cortex (S1), and dorsal premotor cortex (PMd) in healthy volunteers.
Scans were obtained in different sessions before and after 2-h electrical
stimulation applied to the median nerve at the wrist (MNS), to the skin
overlying the shoulder deltoid muscle (DMS), and in the absence of
stimulation (NOSTIM) in a counterbalanced design. We found that baseline
perfusion intensity was comparable within and across sessions. MNS but
not DMS nor NOSTIM led to an increase in signal intensity and number of
voxels activated by performance of median nerve-innervated thumb movements
in M1, S1, and PMd for up to 60 min. Task-related fMRI activation changes
were most prominent in M1 followed by S1 and to a lesser extent in PMd.
MNS elicited a displacement of the center of gravity for the thumb movement
representation towards the other finger representations within S1. These
results indicate that MNS leads to an expansion of the thumb representation
towards other finger representations within S1, a form of plasticity that
may underlie the influence of SS on motor cortical function, possibly
supporting beneficial effects on motor control.
Publication Types:
PMID: 16084740 [PubMed - indexed for MEDLINE]