Connections from the basal ganglia to the thalamus

Many data suggest that the basal gnaglia exerts an indirect influence onto the motor cortex through the thalamus which receives pallidal and nigral efferences. According to the anatomical data, the internal segment of globus pallidus projects to the VL-VA and CM of thalamus and the substantia nigra sends axons ending in the VL and VA with an intranuclear organization which did not overlap the pallidal terminations. The electrophysiological records in the VL-VA nucleus demonstrates that pallidal stimulation induces an inhibitory response, mainly on thalamic neurons, which does not receive cerebellar input. If spreading of excitation is avoided, nigral stimulation also induces an inhibition at the thalamic level. This inhibitory effect can be recorded on relay cells with cerebellar input and cortical output as well as on nonrelay cells. The electrophysiological results in the case of the striatopallidal and striatonigral projections are also briefly reported.