Neural Substrates Associated with Character Amnesia in Chinese Handwriting: A Functional Near-infrared Spectroscopy Study

Chinese speakers have long suffered from character amnesia in handwriting, failing to handwrite a character despite being able to recognize it. However, it remains unclear whether character amnesia arises from the failure in accessing orthographic representations in the orthographic lexicon, reduced graphemic information in the graphemic buffer, or/and weakened phonology-orthography links. To address this issue, we employed functional near-infrared spectroscopy to identify brain regions that are associated with character amnesia. In particular, we tested whether character amnesia is associated with deactivation in the fusiform gyrus (FG), the superior parietal gyrus (SPG), or the supramarginal gyrus (SMG), which have been shown to be respectively associated with the orthographic lexicon, graphemic buffer, and phonology-orthography conversion. In a handwriting-to-dictation task, 23 Cantonese-speaking adults handwrote a character according to a dictation prompt and then reported whether they correctly handwrote the character or suffered from character amnesia. Functional near-infrared spectroscopy results showed that, compared with correct handwriting, character amnesia elicited reduced activation in the bilateral FG, the SPG, and the SMG. Parametric analyses showed that character frequency and number of strokes positively correlated with activation of the FG and the SPG, respectively. Functional connectivity analyses revealed that, compared with correct handwriting, character amnesia was associated with decreased connectivity between the left FG and the left SMG, the right FG and the right SMG, the right FG and the right SPG, the right FG and the left SMG, and the right FG and the left SPG. Together, these results suggest that character amnesia is associated with decayed orthographic representations (in the orthographic lexicon) and failure in phonology-orthography conversion, resulting in reduced orthographic information being retrieved (into the graphemic buffer) for handwriting execution.