Vertical alignment in monkeys with unilateral IV section: effects of prolonged monocular patching and trigeminal deafferentation.

We investigated monocular viewing and trigeminal (V) deafferentation on the vertical deviation (VD) in monkeys following intracranial IV section. Two monkeys wore a patch for four to six weeks, one over the paretic eye and the other over the normal eye following IV section. Two other monkeys had combined IV and V section with the paretic eye patched postlesion. In monkeys with IV section alone, the VD lessened within the first week postlesion but then increased gradually with the same eye still patched. Thus binocular viewing was unnecessary for the later VD increase. With combined IV and V section, the VD also transiently lessened postlesion. We have proposed that the decrease in VD after IV section is adaptive, driven by an error signal using ocular proprioception and efference copy. Since V section did not eliminate the early decrease in VD, we suggest some orbital afference is transmitted centrally via other cranial nerves. However, the later increase in VD suggests either that the proprioceptive effect cannot be sustained or that mechanical changes supervene to increase the VD.