Central facial palsy
Encyclopedia
Central facial palsy, is a symptom or finding characterized by paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...

 or paresis
Paresis
Paresis is a condition typified by partial loss of voluntary movement or by impaired movement. When used without qualifiers, it usually refers to the limbs, but it also can be used to describe the muscles of the eyes , the stomach , and also the vocal cords...

 of the lower half of one side of the face
Face
The face is a central sense organ complex, for those animals that have one, normally on the ventral surface of the head, and can, depending on the definition in the human case, include the hair, forehead, eyebrow, eyelashes, eyes, nose, ears, cheeks, mouth, lips, philtrum, temple, teeth, skin, and...

. It usually results from damage to upper motor neuron
Upper motor neuron
Upper motor neurons are motor neurons that originate in the motor region of the cerebral cortex or the brain stem and carry motor information down to the final common pathway, that is, any motor neurons that are not directly responsible for stimulating the target muscle...

s of the facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

.

The facial motor nucleus
Facial motor nucleus
The facial motor nucleus is a collection of neurons in the brainstem that belong to the facial nerve . These lower motor neurons innervate the muscles of facial expression and the stapedius.-Anatomy:...

 has dorsal and ventral divisions that contain lower motor neuron
Lower motor neuron
Lower motor neurons are the motor neurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles...

s supplying the muscles of the upper and lower face, respectively. The dorsal division receives bilateral upper motor neuron input (ie, from both sides of the brain) while the ventral division receives only contralateral input (ie, from the opposite side of the brain).

Thus, lesions of the corticobulbar tract
Corticobulbar tract
The corticobulbar tract is a white matter pathway connecting the cerebral cortex to the brainstem. The 'bulb' is an archaic term for the medulla oblongata; in modern clinical usage, it sometimes includes the pons as well...

 between the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

 and the facial motor nucleus destroy or reduce input to the ventral division, but ipsilateral input (ie, from the same side) to the dorsal division is retained. As a result, central facial palsy is characterized by hemiparalysis or hemiparesis of the contralateral muscles of facial expression, but not the muscles of the forehead
Forehead
For the Arsenal striker see GervinhoIn human anatomy, the forehead is the fore part of the head. It is, formally, an area of the head bounded by three features, two of the skull and one of the scalp. The top of the forehead is marked by the hairline, the edge of the area where hair on the scalp...


Signs and symptoms


Central facial palsy is the paralysis of the lower half of one side of the face. This condition is often caused by a stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

. This condition is often the result of damage of the upper motor neurons of the facial nerve. The facial motor nucleus contains ventral and dorsal areas that have lower motor neurons that supply the upper and lower face muscles. When central facial palsy occurs, there are lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...

s in the corticobulbar tract
Corticobulbar tract
The corticobulbar tract is a white matter pathway connecting the cerebral cortex to the brainstem. The 'bulb' is an archaic term for the medulla oblongata; in modern clinical usage, it sometimes includes the pons as well...

 between the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

. Because of these lesions, the facial motor nucleus will reduce or destroy input in the ventral division. The ipsilateral input in the dorsal region is preserved.

Central facial palsy is often characterized by either hemiparalysis or hemiparesis
Hemiparesis
Hemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....

 of the contra-lateral muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

s in facial expression. Muscles on the forehead are left intact. Also, most patients will have lost voluntary control of the movement of the muscles in the face, however, the muscles in the face that are involved in spontaneous emotional expression will often remain intact. Central Facial palsy occurs in patients who are hemiplegic. Such patients not only have dysfunctions in the facial expression but also a difficulty in communication. Other oropharyngeal functions such as sucking, swallowing, and talking are also impaired.

Central facial paralysis/palsy often has similar characteristics with stroke patients. Because of uncrossed areas from the ipsilateral and the supranuclear areas, movements in the frontalis and upper orbicularis oculi are often spared. Facial movement can be present on the affected side when the person expresses emotion. Damage to the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 motor pathway from the cerebral cortex to the facial nuclei is found in the pons. This will lead to facial weakness that will spare various muscles in the face depending on the type of paralysis. The discrepancy of the weakness between the upper and lower facial muscles are due to the bilateral corticonuclear innervation from the upper facial muscles and contralateral corticonuclear innervation to the lower facial muscles.

The motor system and facial patterns


In contemporary perspectives, the motor cortex
Motor cortex
Motor cortex is a term that describes regions of the cerebral cortex involved in the planning, control, and execution of voluntary motor functions.-Anatomy of the motor cortex :The motor cortex can be divided into four main parts:...

 is composed of two distinct areas; however, this viewpoint is incorrect. The motor cortex is located in the posterior frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...

, and has multiple areas with anatomical and functional regions. Each area is involved in the circuitry of various inputs of sensory
Sense
Senses are physiological capacities of organisms that provide inputs for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception...

 information. The motor and parietal
Parietal
Parietal may refer to:*Parietal placentation*Parietal lobe of the brain*Parietal bone of the skull*Parietal scales of a snake lie in the general region of the parietal bone*Parietal cell in the stomach*Parietal pleura...

 areas are reciprocally intertwined and form a group of specialized circuits that work parallel to one another. These circuits transform sensory information into an action or movement.

The parieto-frontal circuits are the basic compositions of the main elements of the cortical motor system. These circuits are dependent on the motor area in order to receive afferent information from the parietal areas. The input in one area is predominant, containing full amounts of information. The other input area is known as moderate or weak. When the input is moderate or weak, it contains additional secondary information. Each parietal area is connected to several motor areas. However, it only makes privileged contact with one motor area. There are exceptions to this, which include the prefrontal gyrus where the parietal area sends an equal amount of fibers to many motor areas. This interaction is vital because the activity in the facial muscles is due to voluntary control of the direct and indirect pathways that are corticobulbar pathways. Facial muscles will often respond to emotional influences by these pathways also. Most of our emotions are expressed more intensely on the left side than the right side of the face. The reason for the asymmetry
Asymmetry
Asymmetry is the absence of, or a violation of, symmetry.-In organisms:Due to how cells divide in organisms, asymmetry in organisms is fairly usual in at least one dimension, with biological symmetry also being common in at least one dimension....

 however, remains unclear, a commonly concluded theory is that the right side of the hemisphere has an advantage in emotional processing than the left hemisphere. In order to examine facial muscle movement often, transcranial magnetic stimulation
Transcranial magnetic stimulation
Transcranial magnetic stimulation is a noninvasive method to cause depolarization or hyperpolarization in the neurons of the brain...

 (TMS) is used.

Upper motoneuron lesions to the face often cause paralysis. The lesions will cause weakness in various areas of the face while other areas of the face are not impacted. This pattern of weakness due to the input of the motor neurons of the lower facial muscles is often maintained contralateral. The strength of the muscles in the upper region of the face are preserved better than the muscles in the lower face. It was found that in many anataomical studies that cortical input from both hemispheres could reach motoneurons that supply muscles of all aspects of the face. Through the combination of anterograde and retrograde tracing techniques in monkeys it was found that the facial nucleus, which supplies muscles of the lower face are innervated bilaterally. Using TMS has shown the activation of both hemispheres during facial expression and emotion. However, there have been some discrepancies with the use of this method including differences in observations when using single and multiple needles as well as the areas of where the needles are placed. Using electrical cortical mapping bilateral movements were observed in the lower facial muscles compared to unilateral movements. From anatomic studies on patients with unilateral infarction, motoneurons in the lower facial area were innervated bilaterally; however, there was predominance in contralateral areas of the lower face.

Examination techniques


Through electrophysiological studies and neuronal tracing, these characteristics do not fully support the typical person with central facial palsy. Often, transcranial magnetic stimulation (TMS) is used to understand the bilateral corticonuclear projections of the lower facial motor neurons. This idea using bilateral innervation to the upper facial motor neurons is rarely tested by humans because of the afferent fibers in the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

 are distributed over the head and face and could cause damage. Supranuclear motor innervation of the facial musculature is difficult to examine because the circuitry is quite complex, only a few cases are described in literature of central facial palsy and the absence of bilateral perioral muscle responses after TMS of the affected hemisphere. EMG responses are often used to observe the upper facial muscles, however, it is difficult to elicit by TMS, which often works by examining the motor cortex and recording the motor stroked potentials. At high stimulation strengths, this often will excite the trigeminal sensory afferents and will trigger a blink reflex. From the blink reflex, it contains the R1 ipsilateral and bilateral R2 component. The reflex can then be recorded in the lower parts of the brain. The R1 component will limit the evaluation of the ipsilateral responses in the lower facial muscles.

Studies

In one study, the lab group primarily focused on the electrophysiological evaluation of corticonuclear descending fibers to the lower facial motor neurons in patients with central facial palsy, and the discussion of how central facial palsy can become mild from various recovery techniques. It was found that in normal subjects unilateral TMS stimulation of the motor cortex induced EMG responses from the perioral muscles. This finding supports other studies in favor that bilateral projection of the corticonuclear fibers of the lower facial muscles are present in humans and primates with normal function. The study also found that ipsilateral corticonuclear fibers were found in the lower facial muscles, which does not coincide with other papers. The variation could be from the selection of muscles used in the study as well as the different electrodes that were used.

The orbicularis oculi muscles are often examined in patients with facial paralysis. In the study, it was difficult to illicit any corticunuclear EMG responses from this area in both normal subjects and in patients with CFP . This could be because the cortical links and synapses of the upper facial muscles are limited in function and TMS could not presynaptically stimulate the correct areas observed in paralysis. These areas are important because they will stimulate the presynaptic preterminals in cortical neurons. Also, this stimulation to the brain can not be studied on healthy human subjects. The upper facial muscle ME responses could not be innervated by TMS and the low threshold of blink reflex
Reflex
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...

es often interferes with the nature of corticobulbar influences.

Treatment

Electromyographical biofeedback
Biofeedback
Biofeedback is the process of becoming aware of various physiological functions using instruments that provide information on the activity of those same systems, with a goal of being able to manipulate them at will...

 or myofeedback could provide patients who suffer from central facial palsy the ability to create myo-electrical potentials that they will interpret. This method allows patients to receive information about muscle contraction that is normally subliminal. Electromyographical biofeedback enables the patient to regain control of muscles that are involved in facial expression that have been atrophied
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...

. Brener’s model was one of the fist models to describe the circuitry of the role of feedback for voluntary control of physiological processes. His method allows images of feedback that can produce effects on the voluntary control of motor responses, it involves two central systems: an effector mechanism and feedback loops. There are central systems that are the central sensory integration system and the central motor system. The interaction of both of these systems enables the central motor pathways and a central feedback loop that will determine the activity of the effector system when it is innervated by the motor nerve (figure 1).

From this pathway, self instruction will move in a pattern that is called a “response image”. This response is often the actual movement of the directed response. Therefore, by knowing the loop, it allows full or dysfunctional proprioceptive feedback and exteroceptive control of the movement that is necessary in facial muscles.

Neuro developmental treatment

From the knowledge of the sensimotor development a number of other automatic reactions were distinguished, such as balance, support and automatic adaptations of muscle power changes to postures. Patients with hemiplegia will have movements that are lower level and less motor coordination and often have to relearn these movements in order for them to continue or gain normal automatic transitions in the body. Neuro developmental treatment (NDT) often will improve daily functioning and self help. This treatment is centered upon the restoration of the disabilities, specifically those who are hemiplegic with impaired sensimotor and neuropsychological functions. Muscle regulation that is disturbed, often called hypo or hypertonic, will cause abnormal patterns in movement. These automatic reactions are impaired, and patients must learn these movements and remember mentally and physically the positions.

NDT uses techniques of muscle power through inhibiting and stimulating certain muscle groups which aim to lowering or increasing the toneness of the muscle. For facial expression therapists will often assist the patient in making several facial expressions by manipulating certain muscles with fingers. The patient will then try to imitate the expressions of the face. Speech therapy is used in order for word pronunciation
Pronunciation
Pronunciation refers to the way a word or a language is spoken, or the manner in which someone utters a word. If one is said to have "correct pronunciation", then it refers to both within a particular dialect....

to be corrected. NDT is directed at the functioning of the whole body and not just only the face. Understanding the direct mechanisms of the face is needed in order to determine the dysfunction of specific muscles. Although NDT seems to be effective, spontaneous motor movement that is controlled was not examined.
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