SACCADIC PREMOTOR NEURONS IN THE BRAIN-STEM - FUNCTIONAL NEUROANATOMYAND CLINICAL IMPLICATIONS

Saccadic eye movements are generated by immediate premotor excitatory (EBN) and inhibitory (IBN) medium-lead burst neurons, long-lead burst neurons (LBN), and omnipause neurons (OPN) in the brainstem. The histo logical identification of the functional neuron populations is essenti al for performing any neuropathological analysis of clinical cases wit h saccadic disorders. This paper describes the localization of some pr emotor saccadic neurons in human brain and their neurochemistry, based on monkey data. In humans, the EBNs for horizontal saccades (EBN(H)) lie in the paramedian pontine reticular formation in the nucleus retic ularis pontis caudalis (nrpc) and form a compact group of medium-sized neurons. The medium-sized IBNs lie caudal to the nucleus abducens in the nucleus paragigantocellularis dorsalis (pgd). The EBNs for vertica l saccades (EBN(V)) are medium-sized neurons in the rostral interstiti al nucleus of the medial longitudinal fasciculus (riMLF) in the rostra l mesencephalon. The OPNs are located at the midline of the pontine re ticular formation, in the nucleus raphe interpositus, bordered by the EBN area rostrally and the IBN area caudally. The OPNs use glycine as an inhibitory transmitter. These cell groups (EBN(H), EBN(V), IBN, and OPN) were first identified experimentally in monkeys, and all were sh own to express parvalbumin immunoreactivity. The parvalbumin immunorea ctivity was then used as a marker to help identify the homologous neur ons in man.