Directional responses of basal optic neurons are modulated by the nucleus lentiformis mesencephali in pigeons

The nucleus lentiformis mesencephali (nLM) and the nucleus of the basal opt ic root (nBOR) in pigeons are both involved in optokinetic nystagmus. They are reciprocally connected and thus may interact with each other. The prese nt study injected lidocaine into nLM and then examined the effects of nLM b lockade on visual responses of nBOR neurons to target motion. The results i ndicate that nLM could modulate nBOR activity in two ways. First, nLM enhan ces visual responses of 70% of nBOR cells to motion in the preferred direct ions, sharpening their directional tuning. Second, nLM reduces visual respo nses of 13% of nBOR cells to motion in the preferred directions, broadening their directional tuning. The remaining 17% of nBOR cells are not affected by drug application. Taken together with the previous results that nBOR co uld modulate nLM activity (Gu et al., Neuroscience, 104 (2001) 153), it sug gests that both nuclei can mutually modulate each other in generating optok inetic nystagmus. (C) 2001 Elsevier Science Ireland Ltd. All rights reserve d.