Cortical brain mapping of the rat forelimb using fMRI by direct nerve stimulation

This study aims to refine our current knowledge of the cortical motor and sensory representation of four major nerves of the upper extremity: musculocutaneous, ulnar, median and radial nerves. This is achieved by direct electrical nerve stimulation during fMRI acquisition using a 9.4T Bruker scanner. Two distinct current levels (0.5 mA and 1.0 mA) and frequencies (5 Hz and 10 Hz) were used while keeping the duration constant. 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 is being stimulated.