Real-time imaging of the medullary circuitry involved in the generation of spontaneous muscle sympathetic nerve activity in awake human subjects

In order to understand the central neural processes involved in blood pressure regulation we recorded muscle sympathetic nerve activity (MSNA) via a tungsten microelectrode in the common peroneal nerve while performing functional Magnetic Resonance Imaging (fMRI) of the brainstem at 3T. Blood Oxygen Level Dependent (BOLD) changes in signal intensity were measured over 4 s every 8 s (200) volumes. Using the MSNA as the input model, we found that increases in sympathetic outflow were associated with robust increases in signal intensity in the region of the rostal ventrolateral medulla (RVLM). Reciprocal decreases in signal intensity occurred in the regions of the nucleus tractus solitarius (NTS) and caudal ventrolateral medulla (CVLM). We show for the first time that this combined approach of recording sympathetic neural activity and fMRI can provide "real-time" imaging of the neural processes responsible for the generation of sympathetic nerve activity in awake human subjects