Fig. 4-5. NOTE: In all diagrams you are looking out through the subject's eyes. Pathways for conjugate horizontal gaze with schematic representation of eye-movement abnormalities occuring with lesions (shaded areas) in various parts of this system. 1, Occipital cortical lesion associated with depression of contralateral visual pursuit gaze (this may be variable, with some test parameters indicating difficulty with gaze toward the side of the lesion). 2, Premotor frontal lobe lesion encompassing area 8 of the premotor cortex, associated with depression of contralateral voluntary nontracking gaze. 3, Basis pontis or cerebral peduncle lesion associated with depression of contralateral pursuit and voluntary gaze. 4a, Paramedian pontine reticular (pontine gaze center) lesion associated with loss of ipsilateral gaze. 4b, Lesion also encompasses medial longitudinal fasciculus (MLF), causing loss of contralateral adduction. This combination of ipsilateral horizontal gaze deficiency with MLF involvement is aptly called the one-and-a-half synrdrome. 5, Lesions in medial MLF between abducens and oculomotor nuclei are associated with loss of adduction of ipsilateral eye on contralateral horizontal gaze. However, convergence is intact because it is controlled through the upper pons and pretectal region of the midbrain using the intact oculomotor nucleus and nerve. The name for this isolated medial rectus weakness is internuclear ophthalmoplegia (INO).