The basal ganglia are part of the most primitive structures of the human brain.

These groups of nerve cells are responsible for carrying out processes related to implicit learning, the incentive system and the performance of movements, although, as with all parts of the brain, they work in coordination with the rest of the nervous system.

In this article we will see what the basal ganglia are, the functions they carry out, their anatomical and functional characteristics, and some of the main neurological diseases that affect them, summarizing and explaining it in a simple way so that it is easy to understand.

What are basal ganglia?

The cerebral cortex is the most visible part of the human brain, as well as the best known. Its division into two hemispheres as well as four lobes (frontal, parietal, temporal and occipital) has been known and studied since ancient times.

However, the human brain is a complex organ, possessing within it different structures and substructures that are fundamental for the functioning and maintenance of body and cognitive functions, participating in a large number of areas. Examples of these parts of the brain are the hippocampus, the limbic system or the set of nuclei that this article deals with, the basal ganglia .

We call basal ganglia a set of interconnected subcortical nuclei located around the limbic system and the third ventricle. They are located on both sides of the thalamus, at the level of the temporal lobe. These are clusters of grey matter (i.e. areas where the parts of the neurons that are not myelinated are concentrated) that have a large number of connections with other areas of the brain, such as the cortex or thalamus, both at the afferent and efferent levels (they receive information from other brain areas).

The basal ganglia are distributed among areas near the center of the brain, under the cerebral cortex and around the diencephalon, and because of their location they play a role in actions that are between the automatic and the voluntary.

The main neurotransmitters that act in these brain areas are dopamine as an exciter and GABA as an inhibitor component, having different effects depending on the nucleus and the nerve circuits in which they act.

Main components of basal ganglia

Despite being considered as a set of cores given their interconnection, the basal ganglia consists of several differentiated substructures and, in fact, it is physically easy to repair the spaces between them. Below you can find the main structures of this set of brain structures:

1. Grooved body

The groove is considered the main information reception area of the basal ganglia . That is, it is a zone that receives numerous projections from various brain areas, integrating the information and acting with it. It is composed of the neostriated nucleus (composed of caudate nucleus and putamen), which is fundamentally responsible for receiving afferences from the nigrostriatal tract, and the lenticular nucleus (composed of putamen and globus pallidus), which is more focused on sending messages to other cerebral nuclei.

2. Caudate nucleus

Located below the frontal lobe and in connection with the occipital , this structure is linked to the feeling of alarm, warning that something is not working properly, as well as to motivation. This is due to its connections with the frontal lobe, especially with the orbitofrontal cortex.

3. Putamen

Fundamental element in the control of automated movements. Located under the caudate nucleus and connected by the previous zone. It is linked to the movement of the face and extremities .

Globus pallidus

Derived from the diencephalon, it is located between the putamen and the internal capsule . In this case it has myelinated neurons that are used to transmit information to the thalamus and the substantia nigra.

5. Black substance

Located under the thalamus, in the brain stem, this structure is known to be one of the main sources of dopamine in the brain. It actively participates in the brain’s reward system. In its connection with the striatum (part of the nigrostriatal tract) it is also of great importance in the control of fine movement, both of the extremities and the eyes.

6. Nucleus accumbens

Located under the globus pallidus, it receives signals from the ventral tegmental area and sends signals to the globus pallidus . This nucleus participates in the maintenance of behaviour reinforced by drugs and habituation, possessing connections with the limbic system.

7. Subthalamic nucleus

Located at the junction between the midbrain and the thalamus , the main function of the subthalamic nucleus is to regulate motor functions.

8. Red substance

This structure maintains important connections with the cerebellum and spinal cord l , being especially linked to motor coordination. Specifically, it is particularly relevant in the control of arms and shoulder.

Basal ganglia functions

As has been observed in the explanation of its components, the functions of the basal ganglia are varied, participating in numerous and important aspects of our life . Making a general review of the aspects in which they participate, we can say that some of their main functions are the following

1. Planning, integration and control of the voluntary movement

One of the functions for which the basal ganglia are best known is the regulation and management of voluntary motor actions. Acting through the corticostriatal circuit, they act specifically as an unconscious filter that inhibits or selects the movements to be performed , specifically helping to control body posture and to coordinate the fine/precise movement of the extremities.

The basal ganglia allows you to mark the end of a movement, plan sequences and correct them if necessary.

2. Procedural learning

Another aspect in which the basal ganglia have a predominant performance is in procedural learning and in the automation of behavior . This type of learning is that which allows one to become accustomed to carrying out sequences of actions such as those necessary for driving, playing an instrument, shaving or sewing, allowing the management of attention resources so that they can be directed towards other tasks.

3. Executive functions

The basal ganglia also actively participate in the executive functions . In particular, they contribute to maintaining processing speed, planning at the cognitive level and developing strategies for solving problems. Similarly, the connections of the basal ganglia with the orbitofrontal cortex cause them to be involved in behavioural inhibition capacity.

4. Participation in emotional and motivational behavior

As mentioned above, some basal ganglia such as the nucleus accumbens have connections with the limbic system and the brain reward system , given their importance in dopamine management. Thus, the basal ganglia can be considered to be involved in emotional behaviour and drug or stimulation reinforcement.

For example, basal ganglia play a very important role in both classical and operant conditioning.

Disorders linked to basal ganglia problems

As can be seen, all these elements and functions make the basal ganglia fundamental elements for the correct functioning of the organism.

But…, what happens when an injury or an event causes these nuclei not to coordinate or to act as they should? In this case we may find some of the following problems and disorders, generally treating problems of a hypo or hyperkinetic type, that is, linked to movement.

1. Parkinson’s

The most common and best known disorder resulting from a malfunctioning of the basal ganglia is Parkinson’s disease. The most recognizable symptoms of this disorder are the parkinsonian or resting tremors. Muscle rigidity and loss of spontaneous movement also occur, along with marked bradykinesia or loss of motor speed and gait disturbances.

This disorder occurs especially with the degeneration and death of the nigrostriatal dopamine cells , which causes the transmission of dopamine to be largely lost, with no information reaching the motor cortex.

  • Related article: “Parkinson’s: causes, symptoms, treatment and prevention”

2. Huntington’s Korea

This is a genetic neurodegenerative disorder caused by an alteration of a dominant gene on chromosome number four , with complete penetrance. It produces hyperkinetic symptoms: the disease causes uncontrolled dance-like movements (hence the name chorea), and significant loss of executive functions and memory. Deficits are produced mainly by the death of neurons of the caudate nucleus, especially gabaergic and cholinergic neurons.

3. Loss of psychic self-activation syndrome

As mentioned above, basal ganglia is related to personal motivation. An injury to these areas may therefore have serious implications in this respect , as is the case with the syndrome of loss of psychic self-activation or PAP.

This disorder, also known as pure psychic akinesia or loss of initiation or maintenance of action, produces extreme passivity in those who suffer from it, losing the capacity to be interested, spontaneity and motivation. Those who suffer it are able to recognize their deficits, so that they do not present anosognosia, but they present a great indifference to them.

4. Tic disorders and Tourette’s syndrome

In these disorders, such as Tourette’s syndrome, which is characterized by the presentation of movements, vocalizations, gestures or very stereotyped behaviors that are performed unconsciously , there is severe involvement of the basal ganglia. More specifically, it is believed that these disorders may be related to problems in the putamen.

5. Other related disorders

Apart from these disorders, basal ganglia alterations usually occur in a large number of psychological problems. For example, in obsessive-compulsive disorder or ADHD, alterations of these brain systems can and do appear to occur.

Bibliographic references:

  • Alexander, G.E.; DeLong, M.R. & Strick, P.L. (1986). Organización paralela de circuitos funcionalmente segregados que unen los ganglios basales y la corteza. Annu Rev Neurosci.; 9:357 – 381.
  • Kandel, E. R. (2001). Principios de Neurociencia. 1º edición. McGraw-Hill.
  • Melnick, M.E. (2013). Trastornos de los ganglios basales. In: Umphred DA, Burton GU, Lazaro RT, Roller ML, eds. Umphred’s Neurological Rehabilitation. 6ª edición. Filadelfia, PA: Elsevier Mosby; capítulo 20.
  • Morris, M.E.; Iansek, R., Matyas, T.A. & Summers, J.J. (1996). Stride length regulation in Parkinson’s disease. Estrategias de normalización y mecanismos subyacentes. El cerebro. 119:551 – 68.