Connections from the Basal Ganglia to the Thalamus

Abstract

Many data suggest that the basal ganglia 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 demonstrate 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.

Bilateral Improvement in Voluntary Movement after Unilateral Diencephalic Lesions for Parkinsonism

“…Moreover, for the drawing test, the lesion's initial effect (during pre5/ postl) was to improve the contralateral arm more than the ipsilateral one, whereas, for the pegboard test, the contralateral arm tended to be worse directly after surgery while the ipsilateral arm was unchanged. This initial deterioration in timed performance of the contralateral arm was associat ed with a transient dysmetria clinically apparent in some patients while using the limb for the pegboard test on postl, and presumably reflecting a disturbance of pathways that carry proprioceptive and visual feedback to the thalamus and motor cortex [3,7,19,22]. Such a disturbance of coor dination would affect performance with the pegboard rather than the bal listic movement involved in the drawing test.…”

Thalamic afferents to prefrontal cortices from ventral motor nuclei in decision‐making

“…This large array of striatal inputs hints to its diverse and integrative functions related to movement (Feger et al, 1976;Lee, 1984). The description of the innervation from the whole prefrontal cortex into segregated striatal areas, led to the exploration of basal ganglia functions associated with prefrontal cortical functions in monkeys (Graybiel, 1991;Romo et al, 1992;Joel & Weiner, 1994;Jaeger et al, 1995;Afifi, 2003).…”

Basal ganglia: structure and computations

“…A given striopallidal axon can terminate more than once on a given pallidal cell dendrite. Some axons have short collaterals that run in parallel with the parent axon and seem to contact a single dendrite repetitively [72] though numerous afferent fibres may converge on a given dendrite [66]. This suggests limited divergence, each striatal neurone contacting relatively few pallidal cells, but significant convergence, with many striatal neurones contacting each pallidal cell.…”

“…Is there some kind of compression of information into fewer and fewer channels? What should we make of the inhibitory projections between nuclei, with three such connections in apparent series [56,66]? Are these simply devices to invert the sign of outputs, so that inhibitory interactions can occur among output neurones and then be converted back to effectively excitatory outputs?…”