Putamen: Structure, Functions And Related Disorders
The basal ganglia is a subcortical region that is involved in various physical and cognitive functions, particularly movement, both voluntary and automatic. The nuclei that make up this superstructure have been grouped in different ways, giving rise to names that overlap with 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 attention above all to the relationship of this nucleus with the rest of the regions of the basal ganglia.
The putamen is a brain structure that plays a fundamental role in the preparation and execution of limb movements 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, neuron bodies, 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 approximately circular.
The functions of the putamen depend on the neurotransmitters GABA and acetylcholine, as well as enkephalin, an opioid peptide involved in pain perception and its regulation. For its part, gamma-aminobutyric acid or GABA is the main inhibitory neurotransmitter, while acetylcholine (ACh) activates muscle movement.
The putamen, striatum, globus pallidus, caudate nucleus, nucleus accumbens, subthalamic nucleus, substantia nigra, and red substantia 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, since the basal ganglia are located in the brain.
Morphologically and functionally the putamen is intimately related to the caudate nucleus, globus pallidus and nucleus accumbens ; As a whole, these three structures are known as the striatum. Likewise, we call the junction between the putamen and the globus pallidus the “lenticular nucleus.”
The putamen is connected to the substantia nigra and the globus pallidus 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 puten to fulfill these functions.
1. Regulation of movement
The putamen and the rest of the structures that make up the striatum send afferents 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 movement selection, regulation of motor learning and 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 would be due to its connections with other structures, both cortical and subcortical.
2. Operant conditioning
Operant or instrumental conditioning is a type of learning that is based on the positive (reinforcement) or negative (punishment) consequences 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 that which occurs passively, through mere exposure to specific stimuli. Dopamine and acetylcholine are believed to explain this function of the putamen, as occurs with operant conditioning.
4. Category learning
Scientific research suggests that the putamen also influences category learning, that is, broad psychological constructs that encompass 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 with the insula; This route is known as the “hate circuit.” Furthermore, it is believed that the putamen is also part of the motor system that acts as a consequence of these emotions.
Related disorders
Injuries to the putamen cause involuntary movements such as tremors, sudden spasms or choreas (rapid shaking of the feet and hands). These types of motor symptoms are very characteristic of damage to the basal ganglia, as well as 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 that are related to the putamen are 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. By moving them, the discomfort is reduced, so people with this alteration are compelled to shake them. The symptoms appear at rest, making it difficult to fall asleep.
