Basal Ganglia


The basal ganglia are a collection of nuclei deep to the white matter of cerebral cortex. The name includes: caudate, putamen, nucleus accumbens, globus pallidus, substantia nigra, subthalamic nucleus, and historically the claustrum and the amygdala. However, the claustrum and the amygdala do not really deal with movement, nor are they interconnected with the rest of the basal ganglia, so they have been dropped from this section. Other groupings you may hear are the striatum (caudate + putamen + nucleus accumbens), the corpus striatum (striatum + globus pallidus), or the lenticular nucleus (putamen + globus pallidus),


Basal Ganglia functions and connections :


The relationships between the nuclei of the basal ganglia are by no means completely understood. When dealing with the brain, you may sometimes be tempted to think that everything is connected to everything else. Take heart, some fairly simple generalizations and schematics can be drawn.


The caudate and putamen receive most of the input from cerebral cortex; in this sense they are the doorway into the basal ganglia. There are some regional differences: for example, medial caudate and nucleus accumbens receive their input from frontal cortex and limbic areas, and are implicated more in thinking and schizophrenia than in moving and motion disorders. The caudate and putamen are reciprocally interconnected with the substantia nigra, but send most of their output to the globus pallidus


The substantia nigra can be divided into two parts: the substantia nigra pars compacta (SNpc) and the substantia nigra pars reticulata (SNpr). The SNpc receives input from the caudate and putamen, and sends information right back. The SNpr also receives input from the caudate and putamen, but sends it outside the basal ganglia to control head and eye movements. The SNpc is the more famous of the two, as it produces dopamine, which is critical for normal movement. The SNpc degenerates in Parkinson disease, but the condition can be treated by giving oral dopamine precursors.


The globus pallidus can also be divided into two parts: the globus pallidus externa (GPe) and the globus pallidus interna (GPi). Both receive input from the caudate and putamen, and both are in communication with the subthalamic nucleus. It is the GPi, however, that sends the major inhibitory output from the basal ganglia back to thalamus. The GPi also sends a few projections to an area of midbrain (the PPPA), presumably to assist in postural control.