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.

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“…These regions are known to be part of the nociceptive network. Motor cortex activation might originate from antidromic stimulation of the efferent motor fibers as seen in a study by Cho and colleagues [9]. These activated areas are in accordance with those reported for similar studies in rats [53].…”

Imaging brain hemodynamic changes during rat forepaw electrical stimulation using functional photoacoustic microscopy

“…In the present study, rats under a high current of stimulation may induce activations near the cortical brain regions, such as the S1Tr. Five major peripheral nerves pass through forepaws of rats, the musculocutaneous nerve, the lateral cutaneous nerve, the median nerve, the ulnar nerve, and the radial nerve (Cho et al, 2007). Cho et al found that the cortical BOLD response to direct radial nerve stimulation (1.0 mA, 10 Hz, 1 ms) activated the S1Tr and the secondary somatosensory region (S2).…”

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“…Similar pulse duration and frequency was applied during direct nerve stimulation, with no effect on the physiological parameters of the animal (Cho et al, 2007).…”