The basal ganglia are a collection of nuclei found on both sides of the thalamus, outside and above the limbic system, but below the cingulate gyrus and within the temporal lobes. Although glutamate is the most common neurotransmitter here as everywhere in the brain, the inhibitory neurotransmitter GABA plays the most important role in the basal ganglia. [**]
These ganglia, or clusters of nerve cells, are tightly interconnected. They also receive information from several different regions of the cerebral cortex. Once the basal ganglia have processed this information, they return it to the motor cortex via the thalamus.
One of the likely functions of this loop, which operates in conjunction with another one involving the cerebellum, is to select and trigger well co-ordinated voluntary movements.
This role of the basal ganglia in initiating and regulating motor commands becomes clearly apparent in people whose basal ganglia have been damaged, such as patients with Parkinson's disease. These patients display difficulty in starting the movements they have planned, as well as trembling and slowness once they do begin them. [**]
The basal ganglia in mammalian brains is also linked and perhaps central to recalling patterns and acting on them.