Cerebellar connections of the ventral lateral geniculate nucleus in the rat.

The connections between the deep cerebellar nuclei and the ventral lateral geniculate nucleus (LGv) were investigated in rats using orthograde and retrograde transport of horseradish peroxidase. Following injections into the deep cerebellar nuclei there was orthograde transport to the contralateral medial LGv and adjacent zona incerta. Injections restricted to LGv consistently labelled a small cluster of cells in the contralateral posterior interposed nucleus. Injections into regions surrounding LGv produced distinctively different patterns of orthograde and retrograde labelling.

Spatial contrast sensitivity changes after subcortical visual system lesions in the rat.

Spatial contrast sensitivity functions were determined in hooded rats after lesions involving the pretectum (PRT), rostral pretectum and adjacent medial thalamus (PRT +), posterior thalamus (PT), or ventral lateral geniculate nucleus (LGv). PRT and PRT + lesions depressed sensitivity at both high and low spatial frequencies but the high frequency loss was much greater in the latter group. PT lesions depressed sensitivity to frequencies of 0.45 cycles/deg. and above but had no detectable effect upon low frequencies while LGv lesions depressed sensitivity to both high and low frequencies. The discussion relates these results to previous reports of discrimination learning impairments after comparable lesions.

Visual discrimination impairments after lesions in zona incerta or lateral terminal nucleus of accessory optic tract.

Possible visual functions of zona incerta (ZI) and lateral terminal nucleus of the accessory optic tract (LTN) in rats were investigated by comparing the effects of localized lesions on a series of discrimination learning tasks. In Experiment 1 animals with ZI lesions were impaired on a simultaneous black versus white (BW) discrimination but not on a simultaneous horizontal versus vertical (HV) task. Animals with LTN lesions were impaired on HV but not on BW. Rats with ZI lesions were impaired on a successive bright versus dim but not a successive HV discrimination when subsequently tested in Experiment 2. Animals with LTN lesions were impaired on both tasks. The results are related to the possibility that visual intensity information gains access to the motor system through a pathway running from the ventral lateral geniculate nucleus to the basal ganglia via ZI. Since LTN lesions impaired acquisition of a HV discrimination, a task highly susceptible to the effects of geniculostriate ablation, it is suggested that such lesions impair the use of visual information without distroying the sensory channels mediating the discrimination.

The role of the ventral lateral geniculate nucleus and posterior thalamus in intensity discrimination in rats.

The role of several subcortical structures in intensity discrimination was studies by examining the effects of localized lesions on intensity and orientation discrimination. In experiment 1 rats with lesions confined to the ventral lateral geniculate nucleus (LGNv) or posterior thalamus were specifically impaired on postoperative acquisition of the intensity discrimination compared with sham operated controls or rats with destruction of the superior colliculi. The lesions had no effect on the orientation discrimination unless the primary visual pathways were also damaged. The effects of LGNv damage on intensity discrimination were confirmed with much smaller lesions in experiment 2. In experiment 3 it was shown that postoperative retention of the intensity discrimination is also specifically impaired by destruction of LGNv. The results are related to the possiblility that information about intensity and pattern is coded in separate visual pathways.