Pure agraphia following a focal lesion in exner's area: a case study supporting the dual-route and network models of writing.

backgroundPure agraphia represents a rare neuropsychological syndrome in which writing is selectively impaired while other language modalities remain intact, providing a unique window into the specialized cognitive and neural mechanisms that support written language production. Drawing on the dual-route cognitive model that posits separable lexical and sublexical spelling mechanisms (Patterson, Acquired disorders of spelling, 1988; Rapp and Caramazza, J Exp Psychol: Human Perception and Performance 23:1130-152, 1997; Rapp et al., Cogn Neuropsychology 19:1-29, 2002), whereas network models emphasize distributed interactions, this case offers a multilevel analysis of the deficits observed in pure agraphia due to a focal lesion in Exner's area in the left frontal lobe (Chen et al., Sci Rep 9:55129, 2019; Hickok and Poeppel, Nat Rev Neurosci 8:393-402, 2007; Stevens et al., J Neurosci 37:5288-297, 2017; Vigneau et al. NeuroImage 30:1414-432,2006). Exner's area-located in the posterior portion of the left middle frontal gyrus, immediately anterior to the hand region of the primary motor cortex and anterior and inferior to the left Frontal Eye Field- has been implicated in the interface between linguistic and motor aspects of writing. CASE PRESENTATION: The patient was a 47-year-old right-handed male with 14 years of formal education and no prior history of language or writing deficits. Four weeks before admission, his wife reported progressive deterioration in writing, characterized by incorrect word selection and spelling errors. Mild drooling from the right corner of the mouth and food retention on the right side of the tongue subsequently appeared. CT and MRI revealed a left frontotemporal mass lesion with partial haemorrhagic transformation confined to Exner's area in the frontal lobe. Comprehensive neuropsychological and neurolinguistic assessment, including the Aachen Aphasia Test and the Lexicon Model Oriented battery, revealed intact oral language, reading, repetition, copying, and general cognition, in striking contrast to a profound writing impairment. The patient exhibited selective difficulties with irregular words, loanwords, and pseudowords, with writing accuracy declining to 40% for pseudowords and 25% for loanwords, despite 100% reading accuracy. Neuropsychological testing showed only mild deficits in verbal working memory. These findings indicate a mixed central agraphia affecting both lexical and sublexical spelling mechanisms, consistent with Exner's area functioning as a supramodal graphemic convergence hub.

conclusionThis case provides lesion-based evidence for the theoretical dissociation of central writing mechanisms and supports the crucial role of Exner's area acting as a critical integration hub linking phonological, orthographic, and motor processes.