Caudate nucleus

The caudate nucleus is one of the structures that make up the corpus striatum, which is part of the basal ganglia in the human brain. Although the caudate nucleus has long been associated with motor processes because of its relation to Parkinson's disease and Huntington's disease, it also plays important roles in nonmotor functions, such as procedural learning, associative learning, and inhibitory control of action. The caudate is also one of the brain structures that compose the reward system, and it functions as part of the cortico-basal ganglia-thalamo-cortical loop.

Along with the putamen, the caudate forms the dorsal striatum, which is considered a single functional structure; anatomically, it is separated by a large white-matter tract, the internal capsule, so it is sometimes also described as two structures—the medial dorsal striatum (the caudate) and the lateral dorsal striatum (the putamen). In this vein, the two are functionally distinct not because of structural differences, but merely because of the topographical distribution of function.

The caudate nuclei are near the center of the brain, sitting astride the thalamus. There is a caudate nucleus in each hemisphere of the brain. Each nucleus is C-shaped, with a wider "head" (caput in Latin) at the front, tapering to a "body" (corpus) and a "tail" (cauda). Sometimes a part of the caudate nucleus is called the "knee" (genu). The caudate head receives its blood supply from the lenticulostriate artery; the tail of the caudate receives its blood supply from the anterior choroidal artery.

The head and body of the caudate nucleus form part of the floor of the anterior horn of the lateral ventricle. The body travels briefly towards the back of the head; the tail then curves back toward the anterior, forming the roof of the inferior horn of the lateral ventricle. This means that a coronal section (on a plane parallel to the face) that cuts through the tail will also cross the body and head of the caudate nucleus.

The caudate is highly innervated by dopaminergic neurons that originate from the substantia nigra pars compacta (SNc). The SNc is in the midbrain and contains cell projections to the caudate and putamen, using the neurotransmitter dopamine. There are also inputs from various association cortices.

The caudate nucleus integrates spatial information with motor behavior formulation. Selective impairment of spatial working memory in subjects with Parkinson's disease and the knowledge of the disease's impact on the amount of dopamine supplied to the striatum have linked the caudate nucleus to spatial and nonspatial mnemonic processing. Spatially dependent motor preparation has been linked to the caudate nucleus through event-related fMRI analysis techniques. Activity in the caudate nucleus was demonstrated to be greater during tasks featuring spatial and motoric memory demands than those that involved nonspatial tasks. Specifically, spatial working memory activity has been observed, via fMRI studies of delayed recognition, to be greater in the caudate nucleus when the activity immediately preceded a motor response. These results indicate that the caudate nucleus could be involved in coding a motor response. With this in mind, the caudate nucleus could be involved in the recruitment of the motor system to support working memory performance by the mediation of sensory-motor transformations.

The caudate nucleus contributes importantly to body and limbs posture and the speed and accuracy of directed movements. Deficits in posture and accuracy during paw-usage tasks were observed after the removal of caudate nuclei in cats. A delay in initiating performance and the need to shift body position constantly were both observed in cats after partial removal of the nuclei.

In monkeys, after the application of cocaine to the caudate nucleus and the resulting lesions produced, there was a "leaping or forward movement". Because of its association with damage to the caudate, this movement demonstrates the inhibitory nature of the caudate nucleus. The "motor release" caused by this procedure indicates that the caudate nucleus inhibits the tendency for an animal to move forward without resistance.