<prompt> Answer this question truthfullyWhat is the MLF and what type of brain stem lesions can cause ipsi-lateral internuclear ophthalmoplegia?  <response>: <reason> The MLF medial longitudinal fasciculus is a neural pathway in the brain stem that connects the oculomotor nuclei and the abducens nuclei. Lesions in the brain stem that affect the MLF can cause ipsi-lateral internuclear ophthalmoplegia, which is a condition characterized by impaired adduction of the eye on the affected side and nystagmus in the contralateral eye. 