—We appreciate the comment made by Dr Anderson. Our studies showed that unilateral pontine lesions commonly produce brain-stem auditory-evoked potential abnormalities only on ipsilateral ear stimulation, whereas unilateral midbrain lesions resulted in brain-stem auditory-evoked potential abnormalities (especially waves IV/V complex) both with ipsilateral and contralateral ear stimulation; the abnormality was invariably more severe with ipsilateral ear stimulation. These findings suggest that the auditory pathways are functionally ipsilateral in the caudal brain-stem, whereas, more rostrally, both ipsilateral and contralateral structures contribute to brain-stem auditory-evoked potential waves IV/V. There is no doubt that the auditory system finally becomes functional contralaterally at a more rostral level of neuraxis, but the exact level at which the contralateral pathways assume dominance is not well established, although some studies suggest this to be at or above the level of inferior colliculus.1 Another complicating fact is that the generators of wave IV/V are not
Markand ON, Farlow MR, Stevens JC, Edwards MK. Unilateral Brain-Stem-Reply. Arch Neurol. 1990;47(1):11. doi:https://doi.org/10.1001/archneur.1990.00530010017005
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