The anterior superior parietal lobule and its interactions with language and motor areas during writing

Past neuroimaging studies of writing demonstrate activation foci in several regions of the posterior parietal cortex (PPC). The present study aimed to dissociate the role of the superior parietal lobule (SPL) from the other PPC regions using functional magnetic resonance imaging (fMRI) and functional connectivity. First, parametric event-related fMRI permitted the categorical comparison of experimental writing conditions with control conditions that were carefully chosen to match the experimental conditions in terms of variables extraneous to the motor act of writing, such as visual stimulus characteristics, and generating and retrieving verbal information. A selective focus of increased activation in the PPC restricted to the rostral part of the SPL (area PE) in the left hemisphere was demonstrated. Subsequently, functional connectivity analysis showed that area PE flexibly interacts with different language areas depending on the linguistic demands of the writing task. Activity in area PE correlates with the left angular gyrus, a region implicated in reading, when the writing is in response to words that are read; in sharp contrast, when the writing is in response to pictured objects, then area PE correlates with the supramarginal gyrus, a region involved in the articulatory and phonological loop, as well as with prefrontal regions that are involved in the retrieval and selection of semantic information. The results suggest that area PE serves as a critical interface between posterior cortical regions in the left hemisphere involved in language processing and the central motor and sensory regions that are directly involved in the control of movement.