This article reviews the nucleus prepositus hypoglossi (NPH) which has been proved to contribute to generation of horizontal eye movements. In general, the NPH receives inputs from oculomotor related nuclei (e.g. the bilateral NPH, the medial vestibular nucleus and ipsilateral burst neuron areas), and projects directly to the bilateral NPH, the vestibular nuclei, the ocular motor nuclei and vestibulo-cerebellar structures. According to these different neural connections, the NPH has been divided into subdivi-sions. Several types of neural activities relating to eye movements are observed in NPH neurons, most of which are increased during ipsiversive horizontal eye movements. The majority of the neurons encode both eye velocity and position signals (burst-tonic neurons). Some of the neurons project to the abducens nucleus. In addition, a class of NPH cells show a burst of activity during a variety of rapid eye movements in cats (burster-driving neurons). These neurons receive disynaptic vestibular input contralaterally and project to burst neuron areas. There are also NPH cells encoding both eye- and head-velocity signals in monkeys (eye-head-velocity neurons). Lesions of the NPH impair gaze holding, implying that the NPH functions as, at least a part of, the neural integrator. However, saccade feedback and putative smooth-pursuit integrators are not influenced after a partial lesion in the NPH. The results suggest that distinct classes of cells spread over the NPH. In summary, the NPH is involved in several aspects of horizontal eye movements and may also function as a part of the neural integrator.
