The caudate nucleus is formed by a collection of nerve nuclei. It is formed in pairs and is located on the lower side of each cerebral hemisphere, each lateral to the thalamus. The caudate nucleus is classified as part of the basal ganglia and is thus part of important control circuits within the extrapyramidal motor system. It is also strongly interconnected with the prefrontal cortex, the seat of multisensory motion and episodic memory and the control and review of emotional processes.
What is the caudate nucleus?
The paired caudate nucleus, also known simply as the caudate, which is separate for each hemisphere of the brain, is formed by a collection of nerve nuclei and is part of the so-called basal ganglia. Basal ganglia perform important regulatory functions in the extrapyramidal motor system. The caudate is surrounded by nerve fibers that are recognizable as stripes of white matter. The collection of nerve nuclei, together with the putamen and the nucleus accumbens, forms the striatum, or striate body. It is a type of functional unit that receives information from the cortex that is processed, filtered, and edited by the basal ganglia. Feedback of the filtered and processed signals to the cortex is provided by the thalamus. The caudate occupies a certain special role within the basal ganglia because it is strongly interconnected with the prefrontal cortex via nerve cords. As part of the frontal lobe of the cerebrum, the prefrontal cortex is the seat of multisensory motion and episodic memory, so that the caudate is involved in the regulatory circuit of emotional actions and action planning as well as in cognitive processes.
Anatomy and structure
The name caudate nucleus (curved nucleus) is derived from its shape, which is reminiscent of a C or kidney, with a broad “head,” a body, and a tapering of the lower end into an elongated, tail-shaped structure. The two nuclei caudati lie respectively against the lateral ventricles of the right and left cerebral hemispheres and are separated from the laterally adjacent putamen by strips of white matter composed of nerve fibers. The caudate, white matter (nerve fibers), and putamen together form the striatum (striate body), which is a functional unit that is the gateway for the control circuits of the basal ganglia and receives input signals from specific areas of the cortex via glutamatergic nerve fibers. The subject of research is the interconnections of the caudate with the limbic system, where emotions and drive behavior are processed. The limbic system also plays a major role in the body’s “doping system” via the release of opioid endorphins to overcome pain and exhaustion.
Function and tasks
In its capacity as part of the extrapyramidal motor system, the caudate nucleus performs central tasks in the “assembly” and control of voluntary complex movements. Procedural motor memory plays a major role in this process. The learning and training of complex natural movement sequences such as walking, jumping, running is closely linked to the reward system controlled via dopamine as a neurotransmitter. The same applies to learning and training complex movement sequences that were not originally intended for humans, such as riding a two-wheeler or even a unicycle, piloting a car or an airplane. The reward system kicks in when a particular movement or sequence of movements brings us closer to the goal of achieving a particular skill. This process of learning with outcome feedback is not limited to motor performance, but can be applied to complex learning processes in general. Within these processes, the caudate assumes important tasks via its neural circuitry with the prefrontal cortex. In the emotional domain, it assumes control and planning functions. Action checks for appropriateness make it a kind of supervisor, so to speak. In Anglo-Saxon usage, the caudate nucleus is therefore assigned to the Supervisory Attentional System (SAS). Beyond planning and action control, the caudate also controls the activity of the cortex by setting certain threshold potentials, which means that it decides on the importance of sensory messages or other mental cognitions and whether the cortex should react to them.Findings about the functions and tasks of the caudate nucleus have changed and expanded enormously in recent years. For example, the caudate has also been found to play a role in the control of emotional processes such as love, maternal love, and pain memory.
Diseases
Some well-known neuronal diseases, such as Parkinson’s disease, athetoses, and dystonias, as well as PANDAS, tic disorders, and ADHD, are associated with acquired or genetic disorders in the regulatory circuits of the basal ganglia. The diseases and disorders often do not relate to a specific basal ganglion, but to a specific functional unit such as the substantia nigra or the corpus striatum with nucleus caudatum and putamen. Some of the disorders described are caused by genetic defects, i.e., they are inherited. One of the most important disorders associated with caudate dysfunction is the so-called tic disorders, which include Tourette syndrome. Tic disorders manifest themselves in involuntary – not voluntarily controllable – movements of certain limbs or even complex movement patterns. Tic disorders are classified as extrapyramidal hyperkinesias and are likely caused by a genetic defect that leads to caudate dysfunction. Since ADHD is often accompanied by tic symptoms, it is reasonable to assume that both disorders are caused by similar defects. In recent years, caudatus has also been associated with pathological addictive behavior. In people suffering from hyperthymestic syndrome, the opposite problem exists. The episodic memory of those affected is so pronounced that they remember practically everything they have experienced, with all the associated parameters such as dates, weather, moods and the like. The hyperthymestic syndrome is always coupled to an enlarged caudate nucleus.
