Dystonia | |
---|---|
A person with medication-induced dystonia | |
Specialty | Neurology |
Complications | physical disabilities (contractures, torticollis), [1] pain and fatigue [2] |
Causes | hereditary (DYT1); birth injury; head trauma; medication; infection; toxins |
Diagnostic method | genetic testing, electromyography, blood tests, MRI or CT scan |
Treatment | medication, physical therapy, botulinum toxin injection, deep brain stimulation |
Medication | anticholinergics, dopamine agonists |
Dystonia is a neurological hyperkinetic movement disorder in which sustained or repetitive muscle contractions occur involuntarily, resulting in twisting and repetitive movements or abnormal fixed postures. [3] The movements may resemble a tremor. Dystonia is often intensified or exacerbated by physical activity, and symptoms may progress into adjacent muscles. [4]
The disorder may be hereditary or caused by other factors such as birth-related or other physical trauma, infection, poisoning (e.g., lead poisoning) or reaction to pharmaceutical drugs, particularly neuroleptics, [3] or stress. Treatment must be highly customized to the needs of the individual and may include oral medications, chemodenervation botulinum neurotoxin injections, physical therapy, or other supportive therapies, and surgical procedures such as deep brain stimulation.
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There are multiple types of dystonia, and many diseases and conditions may cause dystonia.
Dystonia is classified by:
Physicians use these classifications to guide diagnosis and treatment.
For example, dystonia musculorum deformans (Oppenheim, Flatau-Sterling syndrome): [6]
Also known as torsion dystonia or idiopathic torsion dystonia (old terminology "dystonia musculorum deformans").
These most common dystonias are typically classified as follows:
Name | Location | Description |
---|---|---|
Anismus | muscles of the rectum | Causes painful defecation, constipation; may be complicated by encopresis or fecal incontinence. |
Cervical dystonia (spasmodic torticollis) | muscles of the neck | Causes the head to rotate to one side, to pull down towards the chest, or back, or a combination of these postures. |
Blepharospasm | muscles around the eyes | The patient experiences rapid blinking of the eyes or even their forced closure causing functional blindness. |
Oculogyric crisis | muscles of eyes and head | An extreme and sustained (usually) upward deviation of the eyes often with convergence causing diplopia (double vision). It is frequently associated with backward and lateral flexion of the neck and either widely opened mouth or jaw clenching. Frequently a result of antiemetics such as the neuroleptics (e.g., prochlorperazine) or metoclopramide. Can be caused by Chlorpromazine. |
Oromandibular dystonia | muscles of the jaw and muscles of tongue | Causes distortions of the mouth and tongue. |
Spasmodic dysphonia/Laryngeal dystonia | muscles of larynx | Causes the voice to sound broken, become hoarse, sometimes reducing it to a whisper. |
Focal hand dystonia (also known as musician's or writer's cramp). | single muscle or small group of muscles in the hand | It interferes with activities such as writing or playing a musical instrument by causing involuntary muscular contractions. The condition is sometimes "task-specific", meaning that it is generally apparent during only certain activities. Focal hand dystonia is neurological in origin and is not due to normal fatigue. The loss of precise muscle control and continuous unintentional movement results in painful cramping and abnormal positioning that makes continued use of the affected body parts impossible. |
The combination of blepharospasmodic contractions and oromandibular dystonia is called cranial dystonia or Meige's syndrome.
Symbol | OMIM | Gene | Locus | Alt Name |
---|---|---|---|---|
DYT1 | 128100 | TOR1A | 9q34 | Early-onset torsion dystonia |
DYT2 | 224500 | HPCA | 1p35-p34.2 | Autosomal recessive primary isolated dystonia |
DYT3 | 314250 | TAF1 | Xq13 | X-linked dystonia parkinsonism |
DYT4 | 128101 | TUBB4 [7] | 19p13.12-13 | Autosomal dominant whispering dysphonia |
DYT5a | 128230 | GCH1 | 14q22.1-q22.2 | Autosomal dominant dopamine-responsive dystonia |
DYT5b | 191290 | TH | 11p15.5 | Autosomal recessive dopamine-responsive dystonia |
DYT6 | 602629 | THAP1 | 8p11.21 | Autosomal dominant dystonia with cranio-cervical predilection |
DYT7 | 602124 | unknown | 18p (questionable) | Autosomal dominant primary focal cervical dystonia |
DYT8 | 118800 | MR1 | 2q35 | Paroxysmal nonkinesigenic dyskinesia |
DYT9 | 601042 | SLC2A1 | 1p35-p31.3 | Episodic choreoathetosis/spasticity (now known to be synonymous with DYT18) |
DYT10 | 128200 | PRRT2 | 16p11.2-q12.1 | Paroxysmal kinesigenic dyskinesia |
DYT11 | 159900 | SGCE | 7q21 | Myoclonic dystonia |
DYT12 | 128235 | ATP1A3 | 19q12-q13.2 | Rapid-onset dystonia parkinsonism and alternating hemiplegia of childhood |
DYT13 | 607671 | unknown, near D1S2667 [8] | 1p36.32-p36.13 | Autosomal dominant cranio-cervical/upper limb dystonia in one Italian family |
DYT14 | See DYT5 | |||
DYT15 | 607488 | unknown | 18p11 [9] | Myoclonic dystonia not linked to SGCE mutations |
DYT16 | 612067 | PRKRA | 2q31.3 | Autosomal recessive young onset dystonia parkinsonism |
DYT17 | 612406 | unknown, near D20S107 [10] | 20p11.2-q13.12 | Autosomal recessive dystonia in one family |
DYT18 | 612126 | SLC2A1 | 1p35-p31.3 | Paroxysmal exercise-induced dyskinesia |
DYT19 | 611031 | probably PRRT2 | 16q13-q22.1 | Episodic kinesigenic dyskinesia 2, probably synonymous with DYT10 |
DYT20 | 611147 | unknown | 2q31 | Paroxysmal nonkinesigenic dyskinesia 2 |
DYT21 | 614588 | unknown | 2q14.3-q21.3 | Late-onset torsion dystonia |
DYT24 | 610110 | ANO3 [11] | 11p14.2 | Autosomal dominant cranio-cervical dystonia with prominent tremor |
There is a group called myoclonic dystonia where some cases are hereditary and have been associated with a missense mutation in the dopamine-D2 receptor. Some of these cases have responded well to alcohol. [12] [13]
Other genes that have been associated with dystonia include CIZ1, GNAL, ATP1A3, and PRRT2. [14] Another report has linked THAP1 and SLC20A2 to dystonia. [15]
Symptoms vary according to the kind of dystonia involved. In most cases, dystonia tends to lead to abnormal posturing, in particular on movement. Many individuals with the condition have continuous pain, cramping, and relentless muscle spasms due to involuntary muscle movements. Other motor symptoms are possible including lip smacking. [16]
An accurate diagnosis may be difficult because of the way the disorder manifests itself. Affected individuals may be diagnosed as having similar and perhaps related disorders including Parkinson's disease, essential tremor, carpal tunnel syndrome, temporomandibular joint disorder, Tourette's syndrome, conversion disorder or other neuromuscular movement disorders. It has been found that the prevalence of dystonia is high in individuals with Huntington's disease, where the most common clinical presentations are internal shoulder rotation, sustained fist clenching, knee flexion, and foot inversion. [17] Risk factors for increased dystonia in patients with Huntington's disease include long disease duration and use of antidopaminergic medication. [17]
Primary dystonia is suspected when the dystonia is the only sign and there is no identifiable cause or structural abnormality in the central nervous system. Researchers suspect it is caused by a pathology of the central nervous system, likely originating in those parts of the brain concerned with motor function—such as the basal ganglia and the GABA (gamma-aminobutyric acid) producing Purkinje neurons. The precise cause of primary dystonia is unknown. In many cases it may involve some genetic predisposition towards the disorder combined with environmental conditions. [18]
Meningitis and encephalitis caused by viral, bacterial, and fungal infections of the brain have been associated with dystonia. The main mechanism is inflammation of the blood vessels, causing restriction of blood flow to the basal ganglia. Other mechanisms include direct nerve injury by the organism or a toxin, or autoimmune mechanisms. [19]
Malfunction of the sodium-potassium pump may be a factor in some dystonias. The Na+
-K+
pump has been shown to control and set the intrinsic activity mode of cerebellar Purkinje neurons. [20] This suggests that the pump might not simply be a homeostatic, "housekeeping" molecule for ionic gradients; but could be a computational element in the cerebellum and the brain. [21] Indeed, an ouabain block of Na+
-K+
pumps in the cerebellum of a live mouse results in it displaying ataxia and dystonia. [22] Ataxia is observed for lower ouabain concentrations, dystonia is observed at higher ouabain concentrations. A mutation in the Na+
-K+
pump (ATP1A3 gene) can cause rapid onset dystonia parkinsonism. [23] The parkinsonism aspect of this disease may be attributable to malfunctioning Na+
-K+
pumps in the basal ganglia; the dystonia aspect may be attributable to malfunctioning Na+
-K+
pumps in the cerebellum (that act to corrupt its input to the basal ganglia) possibly in Purkinje neurons. [20]
Cerebellum issues causing dystonia is described by Filip et al. 2013: "Although dystonia has traditionally been regarded as a basal ganglia dysfunction, recent provocative evidence has emerged of cerebellar involvement in the pathophysiology of this enigmatic disease. It has been suggested that the cerebellum plays an important role in dystonia etiology, from neuroanatomical research of complex networks showing that the cerebellum is connected to a wide range of other central nervous system structures involved in movement control to animal models indicating that signs of dystonia are due to cerebellum dysfunction and completely disappear after cerebellectomy, and finally to clinical observations in secondary dystonia patients with various types of cerebellar lesions. It is proposed that dystonia is a large-scale dysfunction, involving not only cortico-basal ganglia-thalamo-cortical pathways, but the cortico-ponto-cerebello-thalamo-cortical loop as well. Even in the absence of traditional "cerebellar signs" in most dystonia patients, there are more subtle indications of cerebellar dysfunction. It is clear that as long as the cerebellum's role in dystonia genesis remains unexamined, it will be difficult to significantly improve the current standards of dystonia treatment or to provide curative treatment." [24]
Various treatments focus on sedating brain functions or blocking nerve communications with the muscles via drugs, neuro-suppression, or selective denervation surgery. [25] Almost all treatments have negative side-effects and risks. A geste antagoniste is a physical gesture or position (such as touching one's chin) that temporarily interrupts dystonia, it is also known as a sensory trick. [26] Patients may be aware of the presence of a geste antagoniste that provides some relief. [27] Therapy for dystonia can involve prosthetics that passively simulate the stimulation. [28]
While research in the area of effectiveness of physical therapy intervention for dystonia remains weak, [29] there is reason to believe that rehabilitation can benefit dystonia patients. [30] Physical therapy can be utilized to manage changes in balance, mobility and overall function that occur as a result of the disorder. [31] A variety of treatment strategies can be employed to address the unique needs of each individual. Potential treatment interventions include splinting, [32] therapeutic exercise, manual stretching, soft tissue and joint mobilization, postural training and bracing, [30] neuromuscular electrical stimulation, constraint-induced movement therapy, activity and environmental modification, and gait training. [31]
Recent research has investigated further into the role of physiotherapy in the treatment of dystonia. A recent study showed that reducing psychological stress, in conjunction with exercise, is beneficial for reducing truncal dystonia in patients with Parkinson's disease. [33] Another study emphasized progressive relaxation, isometric muscle endurance, dynamic strength, coordination, balance, and body perception, seeing significant improvements to patients' quality of life after 4 weeks. [34]
Since the root of the problem is neurological, doctors have explored sensorimotor retraining activities to enable the brain to "rewire" itself and eliminate dystonic movements. The work of several doctors such as Nancy Byl and Joaquin Farias has shown that sensorimotor retraining activities and proprioceptive stimulation can induce neuroplasticity, making it possible for patients to recover substantial function that was lost due to Cervical Dystonia, hand dystonia, blepharospasm, oromandibular dystonia, dysphonia and musicians' dystonia. [35] [36] [37] [38] [39]
Due to the rare and variable nature of dystonia, research investigating the effectiveness of these treatments is limited. There is no gold standard for physiotherapy rehabilitation. [33] To date, focal cervical dystonia has received the most research attention; [31] however, study designs are poorly controlled and limited to small sample sizes. [29]
A baclofen pump has been used to treat patients of all ages exhibiting muscle spasticity along with dystonia. The pump delivers baclofen via a catheter to the thecal space surrounding the spinal cord. The pump itself is placed in the abdomen. It can be refilled periodically by access through the skin. Baclofen can also be taken in tablet form [40]
Botulinum toxin injections into affected muscles have proved quite successful in providing some relief for around 3–6 months, depending on the kind of dystonia. Botox or Dysport injections have the advantage of ready availability (the same form is used for cosmetic surgery) and the effects are not permanent. There is a risk of temporary paralysis of the muscles being injected or the leaking of the toxin into adjacent muscle groups, causing weakness or paralysis in them. The injections must be repeated, as the effects wear off and around 15% of recipients develop immunity to the toxin. There is a Type A and a Type B toxin approved for treatment of dystonia; often, those that develop resistance to Type A may be able to use Type B. [41]
Clonazepam, a benzodiazepine, is also sometimes prescribed. However, for most, their effects are limited and side-effects like mental confusion, sedation, mood swings, and short-term memory loss occur.
One complex case study found that a ketogenic type diet may have been helpful in reducing symptoms associated with alternating hemiplegia of childhood (AHC) of a young child. However, as the researchers noted, their results could have been corollary in nature and not due to the diet itself, though future research is warranted. [42]
Surgery, such as the denervation of selected muscles, may also provide some relief; however, the destruction of nerves in the limbs or brain is not reversible and should be considered only in the most extreme cases. Recently, the procedure of deep brain stimulation (DBS) has proven successful in a number of cases of severe generalised dystonia. [43] DBS as treatment for medication-refractory dystonia, on the other hand, may increase the risk of suicide in patients. However, reference data of patients without DBS therapy are lacking. [44]
The Italian Bernardino Ramazzini provided one of the first descriptions of task-specific dystonia in 1713 in a book of occupational diseases, The Morbis Artificum. [45] In chapter II of this book's Supplementum, Ramazzini noted that "Scribes and Notaries" may develop "incessant movement of the hand, always in the same direction … the continuous and almost tonic strain on the muscles... that results in failure of power in the right hand". A report from the British Civil Service also contained an early description of writer's cramp. In 1864, Solly coined the term "scrivener's palsy" for this condition. These historical reports usually attributed the etiology of the motor abnormalities to overuse. Then, dystonia were reported in detail in 1911, when Hermann Oppenheim, [46] Edward Flatau and Wladyslaw Sterling described some Jewish children affected by a syndrome that was retrospectively considered to represent familial cases of DYT1 dystonia. Some decades later, in 1975, the first international conference on dystonia was held in New York. It was then recognized that, in addition to severe generalized forms, the dystonia phenotype also encompasses poorly-progressive focal and segmental cases with onset in adulthood, such as blepharospasm, torticollis and writer's cramp. These forms were previously considered independent disorders and were mainly classified among neuroses. A modern definition of dystonia was worded some years later, in 1984. During the following years it became evident that dystonia syndromes are numerous and diversified, new terminological descriptors (e.g., dystonia plus, heredodegenerative dystonias, etc.) and additional classification schemes were introduced. The clinical complexity of dystonia was then fully recognized. [47]
Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements, that indicates dysfunction of parts of the nervous system that coordinate movement, such as the cerebellum.
Essential tremor (ET), also called benign tremor, familial tremor, and idiopathic tremor, is a medical condition characterized by involuntary rhythmic contractions and relaxations of certain muscle groups in one or more body parts of unknown cause. It is typically symmetrical, and affects the arms, hands, or fingers; but sometimes involves the head, vocal cords, or other body parts. Essential tremor is either an action (intention) tremor—it intensifies when one tries to use the affected muscles during voluntary movements such as eating and writing—or it is a postural tremor, which occurs when holding arms outstretched and against gravity. This means that it is distinct from a resting tremor, such as that caused by Parkinson's disease, which is not correlated with movement. Unlike Parkinson's disease, essential tremor may worsen with action.
A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, face, head, vocal folds, trunk, and legs. Most tremors occur in the hands. In some people, a tremor is a symptom of another neurological disorder.
Hyperkinesia refers to an increase in muscular activity that can result in excessive abnormal movements, excessive normal movements, or a combination of both. Hyperkinesia is a state of excessive restlessness which is featured in a large variety of disorders that affect the ability to control motor movement, such as Huntington's disease. It is the opposite of hypokinesia, which refers to decreased bodily movement, as commonly manifested in Parkinson's disease.
Progressive supranuclear palsy (PSP) is a late-onset neurodegenerative disease involving the gradual deterioration and death of specific volumes of the brain. The condition leads to symptoms including loss of balance, slowing of movement, difficulty moving the eyes, and cognitive impairment. PSP may be mistaken for other types of neurodegeneration such as Parkinson's disease, frontotemporal dementia and Alzheimer's disease. The cause of the condition is uncertain, but involves the accumulation of tau protein within the brain. Medications such as levodopa and amantadine may be useful in some cases.
Hypokinesia is one of the classifications of movement disorders, and refers to decreased bodily movement. Hypokinesia is characterized by a partial or complete loss of muscle movement due to a disruption in the basal ganglia. Hypokinesia is a symptom of Parkinson's disease shown as muscle rigidity and an inability to produce movement. It is also associated with mental health disorders and prolonged inactivity due to illness, amongst other diseases.
Blepharospasm is a neurological disorder characterized by intermittent, involuntary spasms and contractions of the orbicularis oculi (eyelid) muscles around both eyes. These result in abnormal twitching or blinking, and in the extreme, sustained eyelid closure resulting in functional blindness.
Spasmodic torticollis is an extremely painful chronic neurological movement disorder causing the neck to involuntarily turn to the left, right, upwards, and/or downwards. The condition is also referred to as "cervical dystonia". Both agonist and antagonist muscles contract simultaneously during dystonic movement. Causes of the disorder are predominantly idiopathic. A small number of patients develop the disorder as a result of another disorder or disease. Most patients first experience symptoms midlife. The most common treatment for spasmodic torticollis is the use of botulinum toxin type A.
Intention tremor is a dyskinetic disorder characterized by a broad, coarse, and low-frequency tremor evident during deliberate and visually-guided movement. An intention tremor is usually perpendicular to the direction of movement. When experiencing an intention tremor, one often overshoots or undershoots one's target, a condition known as dysmetria. Intention tremor is the result of dysfunction of the cerebellum, particularly on the same side as the tremor in the lateral zone, which controls visually guided movements. Depending on the location of cerebellar damage, these tremors can be either unilateral or bilateral.
Myoclonic dystonia or Myoclonus dystonia syndrome is a rare movement disorder that induces spontaneous muscle contraction causing abnormal posture. The prevalence of myoclonus dystonia has not been reported, however, this disorder falls under the umbrella of movement disorders which affect thousands worldwide. Myoclonus dystonia results from mutations in the SGCE gene coding for an integral membrane protein found in both neurons and muscle fibers. Those suffering from this disease exhibit symptoms of rapid, jerky movements of the upper limbs (myoclonus), as well as distortion of the body's orientation due to simultaneous activation of agonist and antagonist muscles (dystonia).
Parkinson's disease (PD), or simply Parkinson's, is a long-term neurodegenerative disease of mainly the central nervous system that affects both the motor and non-motor systems of the body. The symptoms usually emerge slowly, and as the disease progresses, non-motor symptoms become more common. Usual symptoms include tremors, slowness of movement, rigidity, and difficulty with balance, collectively known as parkinsonism. Parkinson's disease dementia, falls and neuropsychiatric problems such as sleep abnormalities, psychosis, mood swings, or behavioral changes may arise in advanced stages as well.
Basal ganglia disease is a group of physical problems that occur when the group of nuclei in the brain known as the basal ganglia fail to properly suppress unwanted movements or to properly prime upper motor neuron circuits to initiate motor function. Research indicates that increased output of the basal ganglia inhibits thalamocortical projection neurons. Proper activation or deactivation of these neurons is an integral component for proper movement. If something causes too much basal ganglia output, then the ventral anterior (VA) and ventral lateral (VL) thalamocortical projection neurons become too inhibited, and one cannot initiate voluntary movement. These disorders are known as hypokinetic disorders. However, a disorder leading to abnormally low output of the basal ganglia leads to reduced inhibition, and thus excitation, of the thalamocortical projection neurons which synapse onto the cortex. This situation leads to an inability to suppress unwanted movements. These disorders are known as hyperkinetic disorders.
Camptocormia, also known as bent spine syndrome (BSS), is a symptom of a multitude of diseases that is most commonly seen in the elderly. It is identified by an abnormal thoracolumbar spinal flexion, which is a forward bending of the lower joints of the spine, occurring in a standing position. In order to be classified as BSS, the anterior flexion must be of 45 degrees anteriorly. This classification differentiates it from a similar syndrome known as kyphosis. Although camptocormia is a symptom of many diseases, there are two common origins: neurological and muscular. Camptocormia is treated by alleviating the underlying condition causing it through therapeutic measures or lifestyle changes.
Neuroferritinopathy is a genetic neurodegenerative disorder characterized by the accumulation of iron in the basal ganglia, cerebellum, and motor cortex of the human brain. Symptoms, which are extrapyramidal in nature, progress slowly and generally do not become apparent until adulthood. These symptoms include chorea, dystonia, and cognitive deficits which worsen with age.
Parkinsonian gait is the type of gait exhibited by patients with Parkinson's disease (PD). It is often described by people with Parkinson's as feeling like being stuck in place, when initiating a step or turning, and can increase the risk of falling. This disorder is caused by a deficiency of dopamine in the basal ganglia circuit leading to motor deficits. Gait is one of the most affected motor characteristics of this disorder although symptoms of Parkinson's disease are varied.
Athetoid cerebral palsy, or dyskinetic cerebral palsy, is a type of cerebral palsy primarily associated with damage, like other forms of CP, to the basal ganglia in the form of lesions that occur during brain development due to bilirubin encephalopathy and hypoxic–ischemic brain injury. Unlike spastic or ataxic cerebral palsies, ADCP is characterized by both hypertonia and hypotonia, due to the affected individual's inability to control muscle tone. Clinical diagnosis of ADCP typically occurs within 18 months of birth and is primarily based upon motor function and neuroimaging techniques. While there are no cures for ADCP, some drug therapies as well as speech, occupational therapy, and physical therapy have shown capacity for treating the symptoms.
Kufor–Rakeb syndrome (KRS) is an autosomal recessive disorder of juvenile onset also known as Parkinson disease-9 (PARK9). It is named after Kufr Rakeb in Irbid, Jordan. Kufor–Rakeb syndrome was first identified in this region in Jordan with a Jordanian couple's 5 children who had rigidity, mask-like face, and bradykinesia. The disease was first described in 1994 by Najim Al-Din et al. The OMIM number is 606693.
Neurodegeneration with brain iron accumulation is a heterogenous group of inherited neurodegenerative diseases, still under research, in which iron accumulates in the basal ganglia, either resulting in progressive dystonia, parkinsonism, spasticity, optic atrophy, retinal degeneration, neuropsychiatric, or diverse neurologic abnormalities. Some of the NBIA disorders have also been associated with several genes in synapse and lipid metabolism related pathways. NBIA is not one disease but an entire group of disorders, characterized by an accumulation of brain iron, sometimes in the presence of axonal spheroids in the central nervous system.
Cerebellar degeneration is a condition in which cerebellar cells, otherwise known as neurons, become damaged and progressively weaken in the cerebellum. There are two types of cerebellar degeneration; paraneoplastic cerebellar degeneration, and alcoholic or nutritional cerebellar degeneration. As the cerebellum contributes to the coordination and regulation of motor activities, as well as controlling equilibrium of the human body, any degeneration to this part of the organ can be life-threatening. Cerebellar degeneration can result in disorders in fine movement, posture, and motor learning in humans, due to a disturbance of the vestibular system. This condition may not only cause cerebellar damage on a temporary or permanent basis, but can also affect other tissues of the central nervous system, those including the cerebral cortex, spinal cord and the brainstem.
Non-invasive cerebellar stimulation is the application of non-invasive neurostimulation techniques on the cerebellum to modify its electrical activity. Techniques such as transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) can be used. The cerebellum is a high potential target for neuromodulation of neurological and psychiatric disorders due to the high density of neurons in its superficial layer, its electrical properties, and its participation in numerous closed-loop circuits involved in motor, cognitive, and emotional functions.