Graphesthesia is the ability to recognize writing on the skin purely by the sensation of
touch
In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It is ...
. Its name derives from
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
''graphē'' ("writing") and ''aisthēsis'' ("perception"). Graphesthesia tests combined cortical sensation; therefore, it is necessary that primary sensation be intact.
[Blumenfeld, H. (2010). 'Neuroanatomy Through Clinical Cases' (2nd Edition ed.). Sunderland, Massachusetts: Sinauer Associates Inc.]
During medical or
neurological examination
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 hist ...
graphesthesia is tested in order to test for certain neurological conditions such as;
lesions
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 classifi ...
in
brainstem
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 cont ...
,
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...
,
sensory cortex The sensory cortex can refer informally to the primary somatosensory cortex, or it can be used as a term for the primary and secondary cortices of the different senses (two cortices each, on left and right hemisphere): the visual cortex on the occi ...
or
thalamus
The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...
. 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.
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.
[O'Sullivan, S. B., & Schmitz, T. J. (2007). 'Physical Rehabilitation' (5th Edition ed.). Philadelphia: F.A. Davis Company.]
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 Stereognosis (also known as haptic perception or tactile gnosis) 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, spat ...
if a patient is unable to grasp an object.
Graphesthesia can be considered as a type of synthetic sensation as it involves a complex interaction between three neural components i.e. Tactile sensation, two point discrimination and cortical component that stores infirmation about the symbol/letter that is being traced in the skin and was learned through some previous experience.
References
*Physical Examination and Health Assessment written by Carolyn Jarvis. (printed by Saunders/elsevier). or {{ISBN, 0-7216-9773-9.
Medical library at the University of UtahBiology Online.org
Perception