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.