title: Refining the sensory and motor ratunculus of the rat upper extremity using fMRI and direct nerve stimulation.
abstract: It is well understood that the different regions of the body have cortical representations in proportion to the degree of innervation. Our current understanding of the rat upper extremity has been enhanced using functional MRI (fMRI), but these studies are often limited to the rat forepaw. The purpose of this study is to describe a new technique that allows us to refine the sensory and motor representations in the cerebral cortex by surgically implanting electrodes on the major nerves of the rat upper extremity and providing direct electrical nerve stimulation while acquiring fMRI images. This technique was used to stimulate the ulnar, median, radial, and musculocutaneous nerves in the rat upper extremity using four different stimulation sequences that varied in frequency (5 Hz vs. 10 Hz) and current (0.5 mA vs. 1.0 mA). A distinct pattern of cortical activation was found for each nerve. The higher stimulation current resulted in a dramatic increase in the level of cortical activation. The higher stimulation frequency resulted in both increases and attenuation of cortical activation in different regions of the brain, depending on which nerve was stimulated.
authors.affiliation: Department of Plastic Surgery, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
authors.forename: Younghoon R
authors.initials: YR
authors.lastname: Cho
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Pawela
authors.forename: Rupeng
authors.initials: R
authors.lastname: Li
authors.forename: Dennis
authors.initials: D
authors.lastname: Kao
authors.forename: Marie L
authors.initials: ML
authors.lastname: Schulte
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Runquist
authors.forename: Ji-Geng
authors.initials: JG
authors.lastname: Yan
authors.forename: Hani S
authors.initials: HS
authors.lastname: Matloub
authors.forename: Safwan S
authors.initials: SS
authors.lastname: Jaradeh
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Hudetz
authors.forename: James S
authors.initials: JS
authors.lastname: Hyde
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D004566:Electrodes; D005552:Forelimb / Q000294:innervation*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008991:Monitoring, Physiologic; D051381:Rats