Deep inside the brain lies a collection of nuclei collectively known as the basal ganglia. Most notable, the basal ganglia control a wide range of movements from the eyes to the muscles of the extremities. Basal ganglia disease can cause psychological and physical impairment.
The basal ganglia is a collection of nuclei responsible for feedback from several different sources within the brain. The basal ganglia relay information to the cortex via the thalamus. It is responsible for the control of descending motor pathways and controls excessive or exaggerated movements.
There are several life-altering conditions and diseases associated with the basal ganglia. Many of them are sudden-onset in newborn children or toddlers like PANDAS, while some are only noticeable in older patients such as Parkinson’s.
The Structure Of The Basal GangliaFunction Of The Basal GangliaClinical Significance – The Basal Ganglia And DiseaseCommon Disorders Linked To The Basal GangliaThe Basal Ganglia In VertebratesHow Are Diseases Of The Basal Ganglia Diagnosed?What Treatments Are Available For Diseases Affecting The Basal Ganglia?Conclusion
The Structure Of The Basal Ganglia
Function Of The Basal Ganglia
Clinical Significance – The Basal Ganglia And Disease
Common Disorders Linked To The Basal Ganglia
The Basal Ganglia In Vertebrates
How Are Diseases Of The Basal Ganglia Diagnosed?
What Treatments Are Available For Diseases Affecting The Basal Ganglia?
Conclusion
The basal ganglia is not a singular structure but a combination of structures deep in the basal area of the brain. It is made up of the following.
The Striatum
Thestriatumis made up of spiny neurons, and the subcortical structure of the striatum is divided into the:
The striatum contains interneurons classified into:
The dorsal striatum is involved in sensorimotor activities such as:
The caudate has three regions of connectivity, namely:
The Pallidum
The pallidum is a large structure known as the globus pallidus. With it is a ventral extension known as the ventral pallidum. Although it looks like a single object or mass, it can be divided into two distinct parts.
The medial and lateral segments both contain GABAergic neurons. The result is inhibitory on the target. Each segment participates in distinct neural circuits. The GPi segment receives direct and indirect signals from the striatum. The GPe receives largely from the striatum and relays to the subthalamic nucleus.
Pallidal neurons fire at a high but steady rate even in input absence. Signals to the pallidal neurons from the striatum can cause an increase or reduction in the firing rate.
The Substantia Nigra
The midbrain gray matter section of the basal ganglia is called the substantia nigra. It has two parts, namely:
The SNr/GPi complex works in unison and inhibits the thalamus. The SNc produces dopamine, a powerful neurotransmitter. Dopamine helps to maintain balance in the striatal pathway.
The Subthalamic Nucleus
The only section of the basal ganglia producing the excitatory neurotransmitter glutamate is the subthalamic nucleus and is the diencephalic gray matter section of the ganglia. Its part of the indirect pathway, and its role is stimulation of the SNr-GPi complex. It receives inhibitory input from the globus pallidus and forwards excitatory input to the medial segment.
The Circuit Connections
There is still much debate regarding the ganglia function and circuits and the pathways and divisions, whether they overlap and how they are regulated.
The circuitry of the basal ganglia is divided into five distinct pathways:
Some of the five pathways are explained as follows.
The limbic circuit projections follow the ACC with the hippocampus, insula, and entorhinal cortex into the ventral striatum. From there into the rostrodorsal GPi, the ventral pallidum and rostrodorsal SNr. From there, back into the cortex via the posteromedial section of the medial dorsal nucleus.
The oculomotor loop involves projections from the arcuate premotor and supplementary motor area, from the somatosensory and motor cortex into the putamen. Projecting into the caudolateral SNr and ventrolateral GPI and collectively projected into the cortex from the ventralis lateralis pars oralis and ventralis lateralis pars medialis.
The second oculomotor loop involves projections from the dorsolateral prefrontal cortex, the frontal eye fields, and posterior parietal cortex into the caudate and caudal dorsomedial GPi and ventrolateral SNr. It circles back to the cortex through the lateral ventralis anterior pars magnocellularis.
Neurotransmitters
There are several afferent glutamatergic inputs contained in the basal ganglia. There are many neuropeptides found in the basal ganglia, including:
There are more neuromodulators found in the basal ganglia, such as:
Apart from the chemical interactions, the basal ganglia have a wide-ranging function in the body. Some of the most notable functions are.
The superior colliculus’s layered structure can form 2-dimensional retinotopic visual space maps. When there is a change in a visual point in space, that surge of neural activity in the layers of the superior colliculus directs eye movement to that point.
The basal ganglia send strong inhibitory projection to the superior colliculus, which originates in the SNr or substantia nigra pars reticulata. While the SNr neurons fire at a very high, continuous rate, it pauses at the onset of eye movement. This releases the substantia nigra pars reticulata from inhibition.
Any eye movement is associated with the SNr pause, but only some neurons are more dominant where eye movement is concerned. For example, the caudate nucleus contains some neurons that show activity when there is any eye movement.
Caudate nucleus cells typically fire at a low rate, so the increase in activity is very noticeable when there is eye movement. Activation in the caudate nucleus means there is eye movement. This will inhibit the substantia nigra pars reticulata through direct GABAergic projections. The superior colliculus becomes disinhibited in this process.
Role In Motivation
The role of extracellular dopamine in the body is linked to various motivation levels. The three notable levels are:
The ventral striatum and prefrontal cortex become activated when the thalamus is disinhibited. This increase in D1 leads to reward. The evidence in primate studies shows that the subthalamic nucleus and the globus pallidus are also involved in processing rewards.
Decision Making
There are two parts involved in the decision-making aspect of the basal ganglia. The one generates actions, and the other carries them out.
It is assumed that actions are generated in the cortex, and depending on the context, the basal ganglia will select which action to act on. The cortex can learn an action regardless of the outcome. However, the basal ganglia select actions based on the outcome or greater reward or error.
Working Memory
The basal ganglia can be akin to a gatekeeper where memory is concerned. It decides what may or may not enter working memory. It is believed that the excitatory pathway allows information into the prefrontal cortex.
For the information to stay in the prefrontal cortex, it must continue reverberating. The direct and indirect pathways are mechanisms regulating working memory focus.
There is a group of movement diseases that stem from the basal ganglia. They result in two distinct outcomes.
Hyperkinetic disorders result from a low output from the basal ganglia to the thalamus. This results in the thalamus not having sufficient inhibition of the cortex and thalamic projections. This creates involuntary or uncontrolled movements.
Hypokinetic disorders result from an excess of output from the basal ganglia. This inhibits output from the thalamus to the cortex, and voluntary movement becomes limited.
As is known, the basal ganglia are made up of a single structure, although there are distinctive components such as the putamen and caudate nucleus that have special functions, such as the globus pallidus, which function independently.
The basal ganglia are located in the forebrain’s basal part, the origin of the term basal. The ganglia part of the name is a contradiction in this case. Modern medicine uses the term ganglia to refer to nuclei – the neural clusters of the peripheral nervous system.
The basal ganglia are also commonly referred to as the basal nuclei or the international standard for naming the anatomy – nuclei basales.
Because the basal ganglia are responsible for a network of functions that control movement, several disorders and diseases are linked to affected basal ganglia. The list of diseases or disorders commonly associated are:
All vertebrates have basal ganglia that form a part of the forebrain. Even though it is considered to be the most primitive of vertebrates, the lamprey fish also has anatomically visible elements of pallidal, striatal, and nigral basal ganglia.
Different species of vertebrates have different names for the basal ganglia. The different names in some species are as follows:
One controversy in the comparative anatomy regarding the basal ganglia as a convergent is its development through phylogenesis. The debate is surrounding the degree to which selective processing takes place. This is compared to the corresponding processing contained in the basal ganglia re-entry loops.
Diseases that affect the basal ganglia in newborn children or toddlers often characteristically present as movement disturbances or twitches. Clinical and experimental evidence suggests that the basal ganglia are crucial in the mental state of an individual.
Because other diseases may present similarly in neuroradiological investigations, diagnoses of basal ganglia diseases suggest repeated MRI scans. The frequency of MRI scans will greatly depend on the myelination or development stage of the patient’s brain.
Several radiological and clinical findings will be consulted to establish a firm diagnosis of basal ganglia disease. For early diagnoses of neurometabolic basal ganglia disease, a neuroimaging of the brain in combination with therapies can be used to monitor any minor or major changes.
The following testing methods may be applied to confirm a basal ganglia disease diagnosis –
The brain has a remarkable self-healing method called neuroplasticity, which means the ability to re-wire and heal in time. In basal ganglia disease, neuroplasticity is one of the best treatment methods.
Physiotherapy and repetitive muscle exercise to re-wire neural pathways and strengthen the affected muscles or limbs are used to rehabilitate the body while coping with basal ganglia disease.
Alongside the physical therapy with a physiotherapist and occupational therapist, neurorehabilitation devices should be used between sessions. Here are more options for the effective treatment of basal ganglia disease.
The basal ganglia are important for fine-tuning and controlling voluntary muscle movements. Any disturbance or disease affecting areas within the basal ganglia will present a deviation or lack of control in regular functions.
Many physical impairments resulting from basal ganglia disease or damage often result in a psychological decline and require treatment.
Resources
https://www.frontiersin.org/articles/10.3389/fnsys.2014.00016/full
https://www.webmd.com/children/what-is-pandas-syndrome
https://www.mayoclinic.org/diseases-conditions/parkinsons-disease/symptoms-causes/syc-20376055
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Reference this article:Practical Psychology. (2022, June).Basal Ganglia (Function, Location, Parts).Retrieved from https://practicalpie.com/basal-ganglia/.Practical Psychology. (2022, June). Basal Ganglia (Function, Location, Parts). Retrieved from https://practicalpie.com/basal-ganglia/.Copy
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Practical Psychology. (2022, June).Basal Ganglia (Function, Location, Parts).Retrieved from https://practicalpie.com/basal-ganglia/.Practical Psychology. (2022, June). Basal Ganglia (Function, Location, Parts). Retrieved from https://practicalpie.com/basal-ganglia/.Copy
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