Pallesthesia (\ˌpal-es-ˈthē-zh(ē-)ə\), or vibratory sensation, is the ability to perceive

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

.Campbell, W. W., & DeJong, R. N. (2013). DeJong's the neurologic examination. lectronic resourceWilliam W. Campbell. Philadelphia, PA : Lippincott Williams & Wilkins, c2013. This sensation, often conducted through skin and bone, is usually generated by

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are located on sensory neurons that convert mechanical pressure into action potential, electrical signals tha ...

s such as

Pacinian corpuscles The Pacinian corpuscle (also lamellar corpuscle, or Vater–Pacini corpuscle) is a low-threshold mechanoreceptor responsive to vibration or pressure, found in the skin and other internal organs. In the skin it is one of the four main types of cuta ...

, Merkel disk receptors, and tactile corpuscles. All of these receptors stimulate an

action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

in afferent nerves (sensory

neurons A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

) found in various layers of the skin and body. The afferent neuron travels to the

spinal column The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmen ...

and then to the brain where the information is processed. Damage to the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...

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

can result in a decline or loss of pallesthesia. A diminished sense of vibration is known as ''pallhypesthesia''. To determine whether a patient has diminished or absent pallesthesia, testing can be conducted using a

tuning fork A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs ( ''tines'') formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it ag ...

at 128 Hz by placing it on the skin overlying a bone. This works because bones are good resonators of vibrations.

Receptors

Pacinian corpuscles, Merkel disk receptors, and tactile corpuscles are all encapsulated nerve endings involved in tactile stimulation.Mark F. Bear, Barry W. Connors, Michael A. Paradiso. Neuroscience: Exploring the Brain, 4th Edition, Baltimore, MD: Lippincott Williams & Wilkins, 2014 The Pacinian corpuscles are located within the deeper layer of the skin, under the skin in the subcutaneous tissues, within

muscles Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

, in the

periosteum The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. (At the joints of long bones the bone's outer surface is lined with "articular cartila ...

, and other deeper layers of the body. The Merkel disk receptors are located in the superficial epidermis and in hair follicles, while tactile corpuscles are concentrated heavily in the fingertips. Merkel disk receptors and tactile corpuscles respond best to low frequencies when producing an action potential.

Pathway

The sensory conduction pathway that allows for cognitive recognition of vibration occurs through afferent neurons, also known as sensory neurons. The outside stimulus is a vibration that activates one of the three encapsulated nerve endings based upon where the sensation is felt. The intensity of the vibration must cause the neuron(s) to reach or surpass a threshold in order for an

to be propagated. From here, the signal travels through the

dorsal column–medial lemniscus pathway The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial lemniscus pathway (PCML) is the major sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point dis ...

. The pathway is composed of the dorsal column within the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

and the

medial lemniscus The medial lemniscus, also known as Reil's band or Reil's ribbon (for German anatomist Johann Christian Reil), is a large ascending bundle of heavily myelinated axons that decussate in the brainstem The brainstem (or brain stem) is the pos ...

in the

brain stem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is co ...

. Collectively, the ascending sensory fibers are called the dorsal column because ascending fibers gather at the dorsal funiculus in the spinal cord.Dartmouth. (n.d.). Chapter 7 - Somatosensory Systems. Retrieved December 05, 2017, fro

/ref> The dorsal funiculus is located between the Posterior grey column, dorsal horn and the medial line in the spinal cord. There are three types of neurons in the pathway: first-, second-, and third-order neurons. The first-order neuron is the afferent neuron. It enters the spinal cord through the dorsal root

ganglia A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there a ...

and branches in the spinal cord. Some neurons terminate in the spinal cord, where they contribute to a reflex response. Other neurons continue

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

ly, same side, to the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

. If the neurons are coming from the lower limbs, they are carried by the

fasciculus gracilis ''Fasciculus vesanus'' is an extinct species of stem group, stem-group Ctenophora, ctenophores known from the Burgess Shale of British Columbia, Canada. It is dated to and belongs to middle Cambrian strata. The species is remarkable for its tw ...

into the medulla. If the neurons are coming from the upper limbs; they are carried by the fasciculus cuneatus. In the medulla, at the dorsal column, nuclei of the first-order neuron synapse with the second-order neuron, which then decussates (crosses over to the other side of the

) into the

. The second-order neuron then carries the information to the

ventral posterolateral nucleus The ventral posterolateral nucleus (VPL) is one of the subdivisions of the ventral posterior nucleus in the ventral nuclear group of the thalamus. It relays sensory information from the second-order neurons of the neospinothalamic tract and me ...

of the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

and then the

somatosensory cortex The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bod ...

in the

parietal lobe The parietal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integra ...

. Immediately, the posterior parietal lobe synthesizes the information into a recognizable pattern. The coded information is then sent to the

prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, ...

to devise a motor response to the stimulation. The motor information is sent through

efferent neurons Efferent nerve fibers are axons (nerve fibers) of efferent neurons that exit a particular region. These terms have a slightly different meaning in the context of the peripheral nervous system (PNS) and central nervous system (CNS). The efferent ...

Testing

Routine clinical tests include quantitative vibratory testing and the Rydel-Seiffer tuning fork test. The typical frequency used for the tuning fork is 128 Hz. Some common areas for testing in the bones are the metatarsals, the

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

, the malleoli, the anterior superior

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the posterio ...

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

in the spinal cord,

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

, and the styloid processes of the

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

and

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

. These are particularly good for testing because they are close to the surface of the skin, with only a small amount of muscle over them. To test the perception through the skin, small pads are placed on the fingertips and a pallometer is used. For a bone, the test is conducted by placing a tuning fork on a bony prominence and striking the fork. The amount of force used to strike the fork determines the intensity and duration of the vibration delivered. The lower limbs have a higher threshold than the upper limbs, so a stronger stimulus is needed. For accuracy, homologous sites on both the left and right side of the body need to be tested. The person may lose some perception of pallesthesia when switching sides, probably due to sensory adaptation, as the receptors require a larger threshold to produce an action potential because of previous stimulation. If a person reports

asymmetrical Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...

perception this may indicate an underlining neurological issue, as can a lack of perception when the tuning fork is applied to a normal area after being applied to the abnormal area on the opposite side. Vibration testing is often used to distinguish different

neurological disorders Neurological disorders represent a complex array of medical conditions that fundamentally disrupt the functioning of the nervous system. These Disorder of consciousness, disorders affect the brain, spinal cord, and nerve networks, presenting unique ...

and to understand neurological pathways and functions. It is often conducted in older people because advancing age leads to a decline in vibratory sensation. Older people may have complete loss of vibratory sensation in their toes; to determine if the cause is age or a neurological disorder, it can be useful to compare with another person of the same age.

Disorders

A benefit of pallesthesia testing is that it can be used to identify disorders within the neural pathways. Because there are few areas in the

neural pathway In neuroanatomy, a neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable neurotransmission (the sending of a signal from one region of the nervous system to ano ...

where the sensation and perception of vibration can be disturbed, this testing enables doctors to more accurately diagnose their patients' health. It can help to identify effects of other diseases on the nervous system, such as

diabetes mellitus Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained hyperglycemia, high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or th ...

Neural disorders

Peripheral nervous system

The

is composed of afferent and efferent neurons; disorder of these neurons is called

peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...

. Vibration examination can detect and localize disorders of the peripheral nervous system. A gradual loss of sensation from the toes to the knees is consistent with a peripheral nerve problem, whereas an impairment in perceiving vibration from all extremities is a sign of a posterior column disorder. Impairments classified to the peripheral nervous system and posterior column are indicators of demyelination of afferent neurons from a variety of causes.

= Myelopathy

Myelopathy Myelopathy describes any neurologic deficit related to the spinal cord. When due to trauma, myelopathy is known as (acute) spinal cord injury. When inflammatory, it is known as myelitis. Disease that is vascular in nature is known as vascular ...

is a disorder within the spinal cord. Compression on the spinal cord by bony projections or a displaced disk in the cervical spine are the most common causes of myelopathy. Inflammation, illness, and neurodegenerative, nutritional, and vascular disorders can also contribute to myelopathy. Quantitative vibratory testing can be used to assess a patient with myelopathy when the examiner detects uniform loss of vibration below a certain spinal level. For example, if the examination is normal from the iliac crest to the knees but pallesthesia is absent from the knees to the toes, this would be consistent with myelopathy.

Central nervous system

The

is composed of the spinal cord and the brain. Many neurological studies are conducted on patients with lesions. Scientists can learn about the functions of different brain areas by looking at damage to those areas. Thus, studies have been conducted on lesion patients for pallesthesia. A common disease to the central nervous system is

multiple sclerosis Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...

. In this disease, the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

attacks the

myelin Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

sheath surrounding neurons. Deterioration of the myelin sheath drastically reduces the conduction speed of neurons, thus affecting sensation and motor control of the body. These patients exhibit the largest reduction in pallesthesia. They cannot perceive vibration at 128 Hz; however, studies have shown that 256 Hz can be perceived in young multiple sclerosis patients.

Diabetic neuropathy

Diabetes mellitus Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained hyperglycemia, high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or th ...

is a disorder in which the body cannot break down

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

either because

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the insulin (''INS)'' gene. It is the main Anabolism, anabolic hormone of the body. It regulates the metabol ...

is not produced or the body does not produce enough insulin. This causes glucose to accumulate in the blood. High concentrations of glucose in the blood can injure nerve fibers, resulting in

diabetic neuropathy Diabetic neuropathy includes various types of nerve damage associated with diabetes mellitus. The most common form, diabetic peripheral neuropathy, affects 30% of all diabetic patients. Studies suggests that cutaneous nerve branches, such as the s ...

. In most cases, the nerve damage occurs in afferent neurons in the foot and lower limbs. Nerve damage can be assessed with pallesthesia. If there is an inability to sense the vibration being applied from the tuning fork, then nerve damage has occurred. A doctor then assesses the damage and places the patient on treatment, which in severe cases may include amputation of a foot or limb.

Research

From the early 1950s through the 1970s, pallesthesia was used as a research method for many disorders of the sensory system. Scientists hoped to find a new therapy to reconstruct neuronal outputs. They understood that damage to the central nervous system could not be repaired; however, they hoped to rewire the peripheral nervous system to give patients some of their sensation back. One study looked into the effects of pallesthesia on stroke patients.{{Cite journal, last=Zankel, first=Harry, date=1969, title=Pallesthesia Studies in Stroke Patients, journal=Southern Medical Journal, volume=63, issue=1, pages=8–11, doi=10.1097/00007611-196901000-00002, pmid=5766441 They theorized that sinusoidal stimulation may be an effective therapy; however, the results were inconclusive. It is rare for current research to use pallesthesia because better methods of testing the sensory system have been developed.

References

Sensory systems