Striatum: structure, functions and disorders

The basal ganglia They are fundamental structures for the regulation of movement and reward-motivated learning, among other functions. This part of the brain is made up of various nuclei, among which what we know as the "striated body" stand out..

In this article we will describe the structure and functions of the striatum. We will also explain its relationship with other brain regions and with certain physical and psychological disorders that occur as a result of alterations in the striatum.

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The striatum and basal ganglia

The striatum it is also known as "striated nucleus" and "neostriatum". It is a set of structures located at the subcortical level that in turn is part of the basal ganglia, involved in the regulation of intentional and automatic movements, as well as procedural learning, reinforcement, and planning.

The basal ganglia are located in the prosencephalon (or anterior brain), below the lateral ventricles. They are made up of the caudate nucleus, the putamen, the nucleus accumbens, the olfactory tubercle, the globe pallidus, the substantia nigra, and part of the subthalamus.

Technically the term "striatum" encompasses most of the basal ganglia, with the exception of the substance negra and the subthalamic nucleus, since in the past these structures were conceived as a functionally related; however, thanks to recent research we have more information about the differences between these areas.

Today we call the set "striated" composed of the caudate nucleus, the putamen and the nucleus accumbens, which connects the two previous structures. For its part, the concept "striatum" is used above all to designate the combination of the striatum and the globe pallidus.

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Structure and connections

The striatum is made up of two main sections: the dorsal and ventral striatum. The former includes the putamen, globe pallidus, and the caudate and lenticular nuclei, while the ventral striatum is formed by the nucleus accumbens and the olfactory bulb.

Most of the neurons that make up the striatum are medium spiny neurons, named after the shape of their dendrites. We can also find Deiter neurons, which have long dendrites with few branches, and interneurons, especially cholinergic and catecholaminergic.

The caudate and putamen, which together form the neostriatum, receive input from the cerebral cortex, constituting the most important route by which information reaches the basal ganglia.

In contrast, the basal ganglia efferences start mainly from the globe pallidus, which, as we have said, forms part of the striatum according to the classical definition, but not the striatum as such. GABAergic efferences are sent from the pale globe (and therefore inhibitory) indirectly to the premotor cortex, responsible for voluntary movement.

Functions of the striatum

Together, the basal ganglia carry out a wide variety of functions, mainly related to motor skills. These cores contribute to the correct functioning of the following processes:

• Motor learning.
• Procedural memory processing.
• Beginning of voluntary movements.
• Regulation of voluntary movements: direction, intensity, amplitude ...
• Execution of automatic movements.
• Beginning of eye movements.
• Regulation of working (or operational) memory.
• Focus of attention.
• Regulation of motivated behavior (based on dopamine).
• Selection of actions based on the expected reward.

The striatum is related to most of these functions, constituting the most important part of the basal ganglia. Specifically, the ventral striatum average learning and motivated behavior through the secretion of dopamine, while the dorsal section is involved in movement control and executive functions.

Related disorders

Most disorders and diseases related to the striatum affect movements, both voluntary and automatic. The disease of Parkinson's and Huntington's are two basic examples of basal ganglia dysfunction.

However, certain psychological alterations seem to be influenced by the functioning of this structure, mainly in relation to its role in the brain's reward system.

1. Parkinson's disease

Parkinson's disease causes lesions in the brain, mainly in the basal ganglia. The death of dopaminergic neurons in the substantia nigra it interferes with the release of dopamine in the striatum, causing motor symptoms such as slowness, rigidity, tremors and postural instability. There are also symptoms of a depressive type.

2. Huntington's disease

During its initial phase, Huntington's disease mainly affects the striatum; This explains why early symptoms are related to motor control, emotions and executive functions. In this case the basal ganglia are unable to inhibit unnecessary movements, so hyperkinesia occurs.

3. Bipolar disorder

Research suggests that in some cases of bipolar disorder there are alterations in the genes that regulate the function of the striatum. Evidence in this regard has been found for both type I and type II bipolar disorder.

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4. Obsessive-compulsive disorder and depression

The obsessive compulsive disorder and depression, which have a similar biological basis, have been associated with dysfunctions in the striatum. This would explain the decrease in mood that occurs in both disorders; Difficulty inhibiting movements is also relevant in OCD.

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5. Addictions

Dopamine is a neurotransmitter involved in the brain's reward system; the pleasant sensations we feel when dopamine is released in the basal ganglia explain our motivation to return to seek experiences that we know to be pleasant. This explains addictions from a physiological point of view.