Testing for the dual-route cascade reading model in the brain: an fMRI effective connectivity account of an efficient reading style.

Neuropsychological data about the forms of acquired reading impairment provide a strong basis for the theoretical framework of the dual-route cascade (DRC) model which is predictive of reading performance. However, lesions are often extensive and heterogeneous, thus making it difficult to establish precise functional anatomical correlates. Here, we provide a connective neural account in the aim of accommodating the main principles of the DRC framework and to make predictions on reading skill. We located prominent reading areas using fMRI and applied structural equation modeling to pinpoint distinct neural pathways. Functionality of regions together with neural network dissociations between words and pseudowords corroborate the existing neuroanatomical view on the DRC and provide a novel outlook on the sub-regions involved. In a similar vein, congruent (or incongruent) reliance of pathways, that is reliance on the word (or pseudoword) pathway during word reading and on the pseudoword (or word) pathway during pseudoword reading predicted good (or poor) reading performance as assessed by out-of-magnet reading tests. Finally, inter-individual analysis unraveled an efficient reading style mirroring pathway reliance as a function of the fingerprint of the stimulus to be read, suggesting an optimal pattern of cerebral information trafficking which leads to high reading performance.

Transition from rest to movement: brain correlates revealed by functional connectivity.

It is suggested that resting state networks reflecting correlated neural regional activities participate significantly in brain functioning. A fundamental issue is to understand how these networks interact and how their activities change during behavioral transitions. Our aim was to understand better with functional MRI connectivity how the brain switched from a "resting" to a movement-related state by exploring the transitory readiness state for an intended movement of the right hand. Our study does not address movement preparation occurring in a time scale of milliseconds before movement which has been widely studied but movement-readiness which can last longer. At rest, in the absence of overt goal-directed behavior, a "default-mode" network, whose main areas are the posterior cingulate cortex and precuneus (PCC/Pcu), shows high activity interpreted as day dreaming, free association, stream of consciousness, and inner rehearsal. We found that, during rest, the "default-mode" network and the sensorimotor network were not functionally correlated. During movement-readiness, the two networks were functionally correlated through an interaction between the PCC/Pcu and the medial superior parietal cortex in the upper precuneus. The complex PCC/Pcu has been shown to be involved in retrieval and/or setting up spatial attributes for motor imagery, and thus, would be a key region in the movement-readiness phase. It might functionally connect to the medial superior parietal cortex to initiate the movement programming through retrieval of suited movement parameters. The anterior cingulum, functionally correlated to the primary sensorimotor cortex during movement-readiness would have a motivational role or could generate predictions about the movement.

Piecemeal recruitment of left-lateralized brain areas during reading: a spatio-functional account.

Neuroimaging studies of reading converge to suggest that linguistically elementary stimuli are confined to the activation of bilateral posterior regions, whereas linguistically complex stimuli additionally recruit left hemispheric anterior regions, raising the hypotheses of a gradual bilateral-to-left and a posterior-to-anterior recruitment of reading related areas. Here, we tested these two hypotheses by contrasting a repertoire of eight categories of stimuli ranging from simple orthographic-like characters to words and pseudowords in a single experiment, and by measuring BOLD signal changes and connectivity while 16 fluent readers passively viewed the stimuli. Our results confirm the existence of a bilateral-to-left and posterior-to-anterior recruitment of reading related areas, straightforwardly resulting from the increase in stimuli's linguistic processing load, which reflects reading processes: visual analysis, orthographic encoding and phonological decoding. Connectivity analyses strengthened the validity of these observations and additionally revealed an enhancement of the left parieto-frontal information trafficking for higher linguistic processing. Our findings clearly establish the notion of a gradual spatio-functional recruitment of reading areas and demonstrate, to the best of our knowledge, the first evidence of a robust and staged link between the level of linguistic processing, the spatial distribution of brain activity and its information trafficking.