Human cardiovascular and gustatory brainstem sites observed by functional magnetic resonance imaging

The reflex control and relay to higher brain sites of visceral sensory information within the central nervous system is mediated via discrete sites in the brainstem. Anatomical characterization of these sites in humans has been limited due to the invasive nature of such research. The present study employed 4 Tesla functional magnetic resonance imaging (fMRI) to characterize brainstem sites involved in autonomic control in the human. Eight subjects performed tasks that activate the general visceral (the isometric hand-grip, maximal inspiration, Valsalva maneuver) or special visceral sensory systems (sucrose administration to the tongue). Activation of the nucleus of the solitary tract and parabrachial nucleus was consistently observed with all general visceral tasks. Periaqueductal gray area activation was observed during the maximal inspiration and Valsalva maneuver conditions and raphe activation was present in response to isometric hand-grip and maximal inspiration tasks. The activation in the nucleus of the solitary tract was consistently more rostral in the medulla during sucrose administration than during performance of the other experimental tasks. This finding is consistent with what has been previously demonstrated in animals. This is the first study to image the human brainstem with respect to visceral control and demonstrates the feasibility of using high-resolution fMRI to study the functional organization of the human brainstem.