Central facial palsy (colloquially referred to as central seven) is a symptom or finding characterized by paralysis or

paresis In medicine, paresis () is a condition typified by a weakness of voluntary movement, or by partial loss of voluntary movement or by impaired movement. When used without qualifiers, it usually refers to the limbs, but it can also be used to desc ...

of the lower half of one side of the

face The face is the front of an animal's head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may aff ...

. It usually results from damage to

upper motor neuron Upper motor neurons (UMNs) is a term introduced by William Gowers in 1886. They are found in the cerebral cortex and brainstem and carry information down to activate interneurons and lower motor neurons, which in turn directly signal muscles t ...

s of the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste ...

. The facial motor nucleus has dorsal and ventral divisions that contain

lower motor neuron Lower motor neurons (LMNs) are motor neurons located in either the anterior grey column, anterior nerve roots (spinal lower motor neurons) or the cranial nerve nuclei of the brainstem and cranial nerves with motor function (cranial nerve low ...

s supplying the muscles of the upper and lower face, respectively. The dorsal division receives

bilateral Bilateral may refer to any concept including two sides, in particular: *Bilateria, bilateral animals *Bilateralism, the political and cultural relations between two states *Bilateral, occurring on both sides of an organism ( Anatomical terms of l ...

upper motor neuron input (i.e. from both sides of the brain) while the ventral division receives only

contralateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

input (i.e. from the opposite side of the brain). Thus, lesions of the

corticobulbar tract In neuroanatomy, the corticobulbar (or corticonuclear) tract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata (also called ...

between the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...

and

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Va ...

and the facial motor nucleus destroy or reduce input to the ventral division, but

ipsilateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

input (i.e. from the same side) to the dorsal division is retained. As a result, central facial palsy is characterized by hemiparalysis or

hemiparesis Hemiparesis, or unilateral paresis, is weakness of one entire side of the body ('' hemi-'' means "half"). Hemiplegia is, in its most severe form, complete paralysis of half of the body. Hemiparesis and hemiplegia can be caused by different medi ...

of the contralateral

muscles of facial expression The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, al ...

, but not the muscles of the forehead.

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. 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 A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classif ...

s in the

between the

. Because of these lesions, the facial motor nucleus reduces or destroys input in the ventral division. The ipsilateral input in the dorsal region is preserved. Central facial palsy is often characterized by either hemiparalysis or

of the contralateral muscles in facial expression. Muscles on the forehead are left intact. Also, most patients have lost voluntary control of muscle movement in the face—however, muscles in the face involved in spontaneous emotional expression often remain intact. Central Facial palsy occurs in patients who are

hemiplegic Hemiparesis, or unilateral paresis, is weakness of one entire side of the body ('' hemi-'' means "half"). Hemiplegia is, in its most severe form, complete paralysis of half of the body. Hemiparesis and hemiplegia can be caused by different medic ...

. Such patients not only have dysfunctions in the facial expression but also a difficulty in communication. Other

oropharyngeal The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...

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 The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

motor pathway from the cerebral cortex to the facial nuclei is found in the pons. This leads to facial weakness that spares 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 The motor cortex is the region of the cerebral cortex believed to be involved in the planning, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...

is composed of two distinct areas; however, this viewpoint is incorrect. The motor cortex is located in the posterior

frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove be ...

, and has multiple areas with anatomical and functional regions. Each area is involved in the circuitry of various inputs of sensory information. The motor and parietal 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 depend on the motor area 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. Exceptions to this 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 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 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. To examine facial muscle movement often,

transcranial magnetic stimulation Transcranial magnetic stimulation (TMS) is a noninvasive form of brain stimulation in which a changing magnetic field is used to induce an electric current at a specific area of the brain through electromagnetic induction. An electric pulse gener ...

(TMS) is used. Upper motoneuron lesions to the face often cause paralysis. The lesions cause weakness in various areas of the face while not affecting other areas of the face. 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 anatomical 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.

Diagnosis

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 In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chew ...

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 excites the trigeminal sensory afferents and triggers 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 limits the evaluation of the ipsilateral responses in the lower facial muscles.

Treatment

Electromyographical biofeedback or myofeedback could provide patients who have central facial palsy the ability to create myo-electrical potentials that they can interpret. This method provides patients with 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. Brener's model was one of the first 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 determine the activity of the effector system when it is innervated by the motor nerve (figure 1). From this pathway, self instruction moves 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 sensorimotor 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 have movements that are lower level and less motor coordination, and often must relearn these movements to continue or gain normal automatic transitions in the body. Neuro developmental treatment (NDT) often improves daily functioning and self-help. This treatment centers on reversing disabilities, specifically for patients who are hemiplegic with impaired sensorimotor and neuropsychological functions. Muscle regulation that is disturbed, often called hypo or

hypertonic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane- ...

, causes abnormal movement patterns. These automatic reactions are impaired, and patients must learn these movements and remember mentally and physically the positions. NDT uses muscle power techniques through inhibiting and stimulating certain muscle groups, which aims to lower or increase muscle tone. For facial expression, therapists often help the patient make facial expressions by manipulating specific muscles with their fingers. The patient then tries to imitate the facial expressions. Speech therapy helps correct word

pronunciation Pronunciation is the way in which a word or a language is spoken. This may refer to generally agreed-upon sequences of sounds used in speaking a given word or language in a specific dialect ("correct pronunciation") or simply the way a particular ...

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

Research

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 In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...

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 The orbicularis oculi is a muscle in the face that closes the eyelids. It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and borders of a short ...

muscles are often examined in patients with facial paralysis. In the study, it was difficult to elicit any corticonuclear 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 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 reflexes often interferes with the nature of corticobulbar influences.

References

External links

{{DEFAULTSORT:Central Facial Palsy Medical signs Facial nerve disorders