Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction Central agraphias typically involve language areas of the brain, causing difficulty spelling or with spontaneous communication, and are often accompanied by other language disorders.
Central
Central agraphia occurs when there are both impairments in spoken language and impairments to the various motor and visualization skills involved in writing. All four of these symptoms result from pathway lesions. Gerstmann's syndrome may additionally be present with alexia and mild aphasia. Though written letters are often so poorly formed that they are almost illegible, the ability to spell aloud is often retained. The orientation and correct sequencing of the writing will also be impaired.
Causes
Agraphia has a multitude of causes ranging from strokes, lesions, traumatic brain injury, and dementia. Twelve regions of the brain are associated with handwriting. The four distinct functional areas are the left superior frontal area composed of the middle frontal gyrus and the superior frontal sulcus, the left superior parietal area composed of the inferior parietal lobule, the superior parietal lobule and the intraparietal sulcus and lastly the primary motor cortex and the somatosensory cortex. The eight other areas are considered associative areas and are the right anterior cerebellum, the left posterior nucleus of the thalamus, the left inferior frontal gyrus, the right posterior cerebellum, the right superior frontal cortex, the right inferior parietal lobule, the left fusiform gyrus and the left putamen. specifically the language areas around the sylvian fissure, such as Broca's area, Wernicke's area, and the supramarginal gyrus.
Alzheimer's disease
Agraphia is often seen in association with Alzheimer's disease (AD). Writing disorders can be an early manifestation of AD. In individuals with AD, the first sign pertaining to writing skills is the selective syntactic simplification of their writing. Individuals will write with less description, detail and complexity, and other markers, such as grammatical errors, may emerge. Different agraphias may develop as AD progresses. In the beginning stages of AD, individuals show signs of allographic agraphia and apraxic agraphia. Allographic agraphia is represented in AD individuals by the mixing of lower and upper case letters in words; apraxic agraphia is represented in AD patients through poorly constructed or illegible letters and omission or over repetition of letter strokes. As their AD progresses, so does the severity of their agraphia; they may begin to form spatial agraphia, which is the inability to write in a straight horizontal line, and there are often unnecessary gaps between letters and words. Normal spellers have access to a lexical spelling system that uses a whole-word; when functioning properly, it allows for recall of the spelling of a complete word, not as individual letters or sounds. This system further uses an internal memory store where the spellings of hundreds of words are kept. This is called the graphemic output lexicon and is aptly named in relation to the graphemic buffer, which is the short term memory loop for many of the functions involved in handwriting. When the spelling system cannot be used, such as with unfamiliar words, non-words or words that we do not recognize the spelling for, some people are able to use the phonological process called the sub-lexical spelling system. This system is used to sound out a word and spell it. In AD individuals, memory stores that are used for everyday handwriting are lost as the disease progresses. CART is more likely to be successful in treating lexical agraphia when a few words are trained to mastery than when a large group of unrelated words is trained. Words chosen can be individualized to the patient, which makes treatment more personalized.
During the 1850s, clinicians such as Armand Trousseau and John Hughlings Jackson held the prevailing view that the same linguistic deficiency occurred in writing as well as speech and reading impairments. In 1856, Louis-Victor Marcé argued that written and spoken language were independent of each other; he discovered that in many patients with languages disorders, both speech and writing was impaired. The recovery of written and spoken language was not always parallel suggesting that these two modes of expression were independent. He believed the ability to write not only involved motor control, but also the memory of the signs and their meaning. According to Pitres, Marcé and Ogle were the first to emphasize the dissociation between speech and writing. His work was also strongly influenced by Théodule-Armand Ribot's modular approach to memory. Pitres's clinical case study in 1884 argues for the localization of writing in the brain.