The striatum, striatal compartments and functional subdivisions

Detected by anatomists who dissected the cerebral hemispheres, the main structure of the basal ganglia was defined as corpus striatum by Thomas Willis in the 17th century (Willis, 1664) because of the mixture of gray matter and fiber tracts. Such mixture was 

In primates and in many nonprimate mammals, the striatum is divided by the internal capsule into the caudate nucleus, located dorsomedially, and the putamen, located ventrolaterally. In other mammalian species, including the rat and the mouse, the bundles of the internal capsule traverse the striatum in the form of a brush rather than a plate (Nauta, 1989), and the striatum cannot, therefore, be subdivided in two entities, so that it is often referred to as caudoputamen or caudate-putamen (CPu). 

As mentioned earlier, the striatum is classically divided into (i) dorsal striatum or neostriatum, which includes most of the caudate and putamen, and (ii) ventral striatum, which includes the NAc, the ventromedial parts of the caudate and putamen, and the striatal portion of the olfactory tubercle. 

1990 Gerfen, 2004). The patch compartments of the striatum are characterized by low levels of acetylcholine and high levels of various opiates and substance P. The matrix compartment is characterized by cholinergic and somatostatin-containing neurons. Anatomically, corticostriatal and thalamostriatal projections are closely associated with the striatal matrix, while projections from limbic structures, such as the hippocampus and the amygdala, primarily innervate striatal patches. 

In addition, and superimposed to the compartmental patch/matrix organization, corticostriatal projections determine a tripartite anatomical and functional subdivision of the striatum into motor, associative and limbic territories, which have been the subject of detailed investigations in both the monkey and the rat (reviewed by Joel and Weiner, 2000). 

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