This structure is part of the basal ganglia, one of the most important areas of the brain.
The basal ganglia are a subcortical region that is involved in various physical and cognitive functions, particularly in movement, both voluntary and automatic. The nuclei that make up this superstructure have been grouped in different ways, giving rise to names that overlap each other.
The putamen is one of the sections of the basal ganglia. In this article we will describe the structure, functions, and disorders associated with lesions in the putamen, paying particular attention to the relationship of this nucleus with the rest of the regions of the basal ganglia.
What is the putamen?
The putamen is a brain structure that plays a fundamental role in the preparation and execution of the movements of the limbs. It is part of the anatomical-functional region known as the “basal ganglia”, which regulates voluntary motor skills, automatic habits and procedural learning.
It is made up of gray matter, that is, bodies of neurons, unmyelinated dendrites and glial cells. It is located below the cerebral hemispheres, at the base of the telencephalon and in the central part of the brain. Its shape is roughly circular.
The functions of the putamen depend on the neurotransmitters GABA and acetylcholine, as well as on enkephalin, an opioid peptide involved in the perception of pain and its regulation. For its part, gamma-aminobutyric acid or GABA is the main inhibitory neurotransmitter, while acetylcholine (ACh) activates the movement of muscles.
Structure and anatomy
The putamen, corpus striatum , globe pallidus, caudate nucleus, nucleus accumbens, subthalamic nucleus, substantia nigra, and substance red form the basal ganglia. The putamen is the outermost of these nuclei.
The word “ganglion” is normally used to designate groupings of neuronal bodies that are located in the peripheral nervous system, so the nomenclature is paradoxical in this case, as the basal ganglia are located in the brain.
Morphologically and functionally, the putamen is closely related to the caudate nucleus, the globus pallidus, and the nucleus accumbens ; as a whole, these three structures are known as the striatum. Likewise, we call the “lenticular nucleus” the junction between the putamen and the globe pallidus.
The putamen is connected to the substantia nigra and the globe pallus by different nerve pathways. This allows the exchange of information between the basal ganglia and the cerebral cortex, with the thalamus fulfilling its usual role as a relay nucleus.
Functions of the putamen
The two main functions of the putamen are the regulation of movement and the facilitation of different types of learning. It is also involved in disgust and the feeling of hatred.
Let’s see what are the pathways and mechanisms that allow the putamen to fulfill these functions.
1. Regulation of movement
The putamen and the other structures that make up the striatum send afferences to the brain stem, to the regions of the thalamus involved in movement, and to the motor cortex. These signals ensure that locomotion occurs properly.
Other motor activities related to the putamen are the selection of movements, the regulation of motor learning and the planning of motor sequences. This structure is considered to be important especially for the control of the arms and legs.
However, a motor function is not attributed to the putamen specifically, but this role is due to its connections with other structures, both cortical and subcortical.
2. Operant conditioning
The operant conditioning is a type of learning that is based on the positive consequences (reinforcement) or negative (punishment) of behavior. Dopaminergic and cholinergic neurons that are abundant in the basal ganglia play a key role in this regard.
3. Implicit learning
Implicit learning is one that occurs passively, through mere exposure to certain stimuli. Dopamine and acetylcholine are believed to account for this function of the putamen, as is the case with operant conditioning.
4. Learning categories
Scientific research suggests that the putamen also influences the learning of categories, that is, broad psychological constructs that encompass other more specific ones. For example, the category “animal” encompasses the concepts “elephant”, “fish” and “fox”.
5. Disgust, contempt and hatred
The putamen has been theorized to be involved in feelings of disgust and contempt due to its connections to the insula ; this route is known as the “hate circuit”. In addition, it is believed that the putamen is also part of the motor system that acts as a consequence of these emotions.
Injuries to the putamen cause involuntary movements such as tremors, sudden spasms, or choreas (rapid jerking of the feet and hands). These types of motor symptoms are very characteristic of damage in the basal ganglia, as well as in the cerebellum, which is functionally related to these nuclei.
Various neurodegenerative diseases cause motor symptoms of this type because they destroy tissues of the putamen and other basal ganglia. In particular, Parkinson’s disease, Huntington’s disease and Lewy body dementia stand out.
Other psychological and neurological disorders associated with the putamen include attention deficit hyperactivity disorder, Tourette syndrome, schizophrenia, obsessive-compulsive disorder, and some types of depression.
Likewise, damage to this structure can cause restless legs syndrome, a disorder characterized by a feeling of discomfort in the lower extremities. When moving them, the discomfort is reduced, so that people with this alteration are compelled to shake them. The symptoms appear in a state of rest, making it difficult to fall asleep.