Visuomotor relearning after brain damage crucially depends on the integrity of the ventrolateral thalamic nucleus

The role of the ventrolateral thalamic nucleus (VL) has been analyzed in the phase of motor recovery that takes place when the execution of a previously learned movement has been perturbed by damage to another brain area. Cats were trained to perform a reaching movement toward a moving target-spot; they underwent bilateral brain lesions after performance had stabilized. A VL lesion induced a very transient increase of reaction time. The lesion of the main thalamic relay of the visual extrageniculate pathway (LP) severely disrupted accuracy and reaction time but was followed by full recovery. When both lesions were performed together, the deficits were similar to those induced by LP lesion alone, although they were more pronounced. However, the functional compensation was incomplete, and furthermore, the recovery of accuracy crucially depended on regular testing. These results support the involvement of VL in motor learning or relearning.