The vasoconstrictor supplies to different tissues show distinct patterns of 
ongoing and reflex activity, indicating that they are driven by distinct central 
pathways. Vasomotor tone depends heavily on connections from the brainstem, so 
class-specific vasomotor drives have been sought amongst the sympathetic 
premotor neurons which provide those connections. Premotor neurons of the 
rostral ventrolateral medulla (subretrofacial nucleus) provide most descending 
vasomotor drive. Together, they drive the sympathetic supplies to heart, blood 
vessels and adrenal, but not 'non-cardiovascular' sympathetic responses 
(sweating, pupil dilatation, piloerection, etc.). Individually, they provide 
preferential or selective drives to particular classes of 'cardiovascular' 
sympathetic outflow. Subretrofacial neurons are arranged topographically, 
forming a neural map of the functional class (target tissue), not the body 
region, of the driven outflows. It is still unknown whether other premotor cell 
groups are organised this way. Nor are the premotor pathways to 
'non-cardiovascular' sympathetic nerves yet well-defined.