Graphesthesia

Last updated April 04, 2019

Graphesthesia is the ability to recognize writing on the skin purely by the sensation of touch. Its name derives from Greek graphē ("writing") and aisthēsis ("perception"). Graphesthesia tests combined cortical sensation; therefore, it is necessary that primary sensation be intact.^[1]

Greek is an independent branch of the Indo-European family of languages, native to Greece, Cyprus and other parts of the Eastern Mediterranean and the Black Sea. It has the longest documented history of any living Indo-European language, spanning more than 3000 years of written records. Its writing system has been the Greek alphabet for the major part of its history; other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic, and many other writing systems.

During medical or neurological examination graphesthesia is tested in order to test for certain neurological conditions such as; lesions in brainstem, spinal cord, sensory cortex or thalamus. An examiner writes single numbers or simple letters on the skin (usually the palm) with something that will provide a clear stimulus, such as a broken tongue depressor, pen cap etc. Prior to the start of testing, an agreement may be reached between the examiner and the patient as to the orientation of the letters, although this is often unnecessary, since orientation and size of the figures are rarely an issue. The crucial aspect of testing graphesthesia, as with any sensory testing, is to establish that the patient understands the test, hence the test is commenced, in the hemiplegic patient, on the normal, intact hand. This also allows the examiner to establish the patient's numeracy, since semi-numerate patients may have difficulties performing the task.

A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired. This typically includes a physical examination and a review of the patient's medical history, but not deeper investigation such as neuroimaging. It can be used both as a screening tool and as an investigative tool, the former of which when examining the patient when there is no expected neurological deficit and the latter of which when examining a patient where you do expect to find abnormalities. If a problem is found either in an investigative or screening process, then further tests can be carried out to focus on a particular aspect of the nervous system.

The brainstem is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem includes the midbrain, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included.

The spinal cord is a long, thin, tubular structure made up of nervous tissue, that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord that contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone where it passes through the foramen magnum, and meets and enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women. Also, the spinal cord has a varying width, ranging from 13 mm thick in the cervical and lumbar regions to 6.4 mm thick in the thoracic area.

The patient provides a verbal response identifying the figure that was drawn. If the patient has a speech or language impairment that prevents them from verbalizing an answer, the answer can be selected from a series of images shown to them.^[2] Loss of graphesthesia indicates either parietal lobe damage on the side opposite the hand tested or damage to the dorsal columns pathway at any point between the tested point and the contralateral parietal lobe. The major clinical utility of the test in the 21st century is in the condition, cortico-basal ganglionic degeneration, where, in addition to evidence of basal ganglia dysfunction, the presence of cortical sensory loss is likely to have reasonably high specificity for the diagnosis.

Testing graphesthesia can be substituted for stereognosis if a patient is unable to grasp an object.^[2]

Stereognosis is the ability to perceive and recognize the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temperature, etc. In humans, this sense, along with tactile spatial acuity, vibration perception, texture discrimination and proprioception, is mediated by the dorsal column-medial lemniscus pathway of the central nervous system. Stereognosis tests determine whether or not the parietal lobe of the brain is intact. Typically, these tests involved having the patient identify common objects placed in their hand without any visual cues. Stereognosis is a higher cerebral associative cortical function.

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Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction or an inability to spell. The loss of writing ability may present with other language or neurological disorders; disorders appearing commonly with agraphia are alexia, aphasia, dysarthria, agnosia, and apraxia. The study of individuals with agraphia may provide more information about the pathways involved in writing, both language related and motoric. Agraphia cannot be directly treated, but individuals can learn techniques to help regain and rehabilitate some of their previous writing abilities. These techniques differ depending on the type of agraphia.

Alien hand syndrome (AHS) or Dr. Strangelove syndrome is a condition in which a person experiences their limbs acting seemingly on their own, without control over the actions. The term is used for a variety of clinical conditions and most commonly affects the left hand. There are many similar names used to describe the various forms of the condition but they are often used inappropriately. The afflicted person may sometimes reach for objects and manipulate them without wanting to do so, even to the point of having to use the controllable hand to restrain the alien hand. While under normal circumstances, thought, as intent, and action can be assumed to be deeply mutually entangled, the occurrence of alien hand syndrome can be usefully conceptualized as a phenomenon reflecting a functional "disentanglement" between thought and action.

The parietal lobe is one of the four 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.

Monoplegia is paralysis of a single limb, usually an arm. Common symptoms associated with monoplegic patients are weakness, numbness, and pain in the affected limb. Monoplegia is a type of paralysis that falls under hemiplegia. While hemiplegia is paralysis of half of the body, monoplegia is localized to a single limb or to a specific region of the body. Monoplegia of the upper limb is sometimes referred to as brachial monoplegia, and that of the lower limb is called crural monoplegia. Monoplegia in the lower extremities is not as common of an occurrence as in the upper extremities. Monoparesis is a similar, but less severe, condition because one limb is very weak, not paralyzed. For more information, see paresis.

Acalculia is an acquired impairment in which people have difficulty performing simple mathematical tasks, such as adding, subtracting, multiplying and even simply stating which of two numbers is larger. Acalculia is distinguished from dyscalculia in that acalculia is acquired late in life due to neurological injury such as stroke, while dyscalculia is a specific developmental disorder first observed during the acquisition of mathematical knowledge. The name comes from the Greek "a" meaning "not" and Latin "calculare", which means "to count".

Focal neurologic signs also known as focal neurological deficits or focal CNS signs are impairments of nerve, spinal cord, or brain function that affects a specific region of the body, e.g. weakness in the left arm, the right leg, paresis, or plegia.

Autotopagnosia from the Greek a and gnosis, meaning "without knowledge", topos meaning "place", and auto meaning "oneself", autotopagnosia virtually translates to the "lack of knowledge about one's own space," and is clinically described as such.

Cortical deafness agnosia that is a loss of the ability to perceive any auditory information but whose hearing is intact

Cortical deafness is a rare form of sensorineural hearing loss caused by damage to the primary auditory cortex. Cortical deafness is an auditory disorder where the patient is unable to hear sounds but has no apparent damage to the anatomy of the ear, which can be thought of as the combination of auditory verbal agnosia and auditory agnosia. Patients with cortical deafness cannot hear any sounds, that is, they are not aware of sounds including non-speech, voices, and speech sounds. Although patients appear and feel completely deaf, they can still exhibit some reflex responses such as turning their head towards a loud sound.

Pallesthesia, or vibratory sensation, is the ability to perceive vibration. This sensation, often conducted through skin and bone, is usually generated by mechanoreceptors such as Pacinian corpuscles, Merkel disk receptors, and tactile corpuscles. All of these receptors stimulate an action potential in afferent nerves found in various layers of the skin and body. The afferent neuron travels to the spinal column and then to the brain where the information is processed. Damage to the peripheral nervous system or central nervous system can result in a decline or loss of pallesthesia.

Tactile discrimination is the ability to differentiate information through the sense of touch. The somatosensory system is the nervous system pathway that is responsible for this essential survival ability used in adaptation. There are various types of tactile discrimination. One of the most well known and most researched is two-point discrimination, the ability to differentiate between two different tactile stimuli which are relatively close together. Other types of discrimination like graphesthesia and spatial discrimination also exist but are not as extensively researched. Tactile discrimination is something that can be either more or less severe in different people and two major conditions, chronic pain and blindness, can affect it greatly. Blindness increases tactile discrimination abilities which is extremely helpful for tasks like reading braille. In contrast, chronic pain conditions, like arthritis, decrease a person’s tactile discrimination. One other major application of tactile discrimination is in new prosthetics and robotics which attempt to mimic the abilities of the human hand. In this case tactile sensors function similarly to mechanoreceptors in a human hand to differentiate tactile stimuli.

The Dean-Woodcock Neuropsychological Assessment System (DWNAS) provides a standardized procedure for assessing an individual’s sensory, motor, emotional, cognitive, and academic functioning for both English and Spanish speakers, based on the Cattell-Horn-Carroll Model (CHC). The instrument may be administered by psychologists, that need not have neuropsychological backgrounds.

Posterior cortical atrophy form of dementia

Posterior cortical atrophy (PCA), also called Benson's syndrome, is a form of dementia which is usually considered an atypical variant of Alzheimer's disease (AD). The disease causes atrophy of the posterior part of the cerebral cortex, resulting in the progressive disruption of complex visual processing. PCA was first described by D. Frank Benson in 1988.

A neurological disorder is any disorder of the nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord or other nerves can result in a range of symptoms. Examples of symptoms include paralysis, muscle weakness, poor coordination, loss of sensation, seizures, confusion, pain and altered levels of consciousness. There are many recognized neurological disorders, some relatively common, but many rare. They may be assessed by neurological examination, and studied and treated within the specialities of neurology and clinical neuropsychology.

Bruns apraxia, or frontal ataxia is a gait apraxia found in patients with bilateral frontal lobe disorders. It is characterised by an inability to initiate the process of walking, despite the power and coordination of the legs being normal when tested in the seated or lying position. The gait is broad-based with short steps with a tendency to fall backwards. It was originally described in patients with frontal lobe tumours, but is now more commonly seen in patients with cerebrovascular disease.

A somatosensory disorder is an impairment of the somatosensory system.

Agraphesthesia is a disorder of directional cutaneous kinesthesia or a disorientation of the skin's sensation across its space. It is a difficulty recognizing a written number or letter traced on the skin after parietal damage.

Tactile hallucination is the false perception of tactile sensory input that creates a hallucinatory sensation of physical contact with an imaginary object. It is caused by the faulty integration of the tactile sensory neural signals generated in the spinal cord and the thalamus and sent to the primary somatosensory cortex (SI) and secondary somatosensory cortex (SII). Tactile hallucinations are recurrent symptoms of neurological diseases such as schizophrenia, Parkinson's disease, Ekbom's syndrome and delerium tremens. Patients who experience phantom limb pains also experience a type of tactile hallucination. Tactile hallucinations are also caused by drugs such as cocaine and alcohol.

References

Physical Examination and Health Assessment written by Carolyn Jarvis. (printed by Saunders/elsevier). ISBN 978-0-7216-9773-4 or ISBN 0-7216-9773-9.
Medical library at the University of Utah
Biology Online.org

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↑ Blumenfeld, H. (2010). 'Neuroanatomy Through Clinical Cases' (2nd Edition ed.). Sunderland, Massachusetts: Sinauer Associates Inc.
1 2 O'Sullivan, S. B., & Schmitz, T. J. (2007). 'Physical Rehabilitation' (5th Edition ed.). Philadelphia: F.A. Davis Company.

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[Blumenfeld-1] Blumenfeld, H. (2010). 'Neuroanatomy Through Clinical Cases' (2nd Edition ed.). Sunderland, Massachusetts: Sinauer Associates Inc.

[OS-2] 1 2 O'Sullivan, S. B., & Schmitz, T. J. (2007). 'Physical Rehabilitation' (5th Edition ed.). Philadelphia: F.A. Davis Company.