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Abstract
Neurofibromatosis type 1 (NF1) is one of the most common single gene disorders affecting the human nervous system with a high incidence of cognitive deficits, particularly visuospatial. Nevertheless, neurophysiological alterations in low-level visual processing that could be relevant to explain the cognitive phenotype are poorly understood. Here we used functional magnetic resonance imaging (fMRI) to study early cortical visual pathways in children and adults with NF1. We employed two distinct stimulus types differing in contrast and spatial and temporal frequencies to evoke relatively different activation of the magnocellular (M) and parvocellular (P) pathways. Hemodynamic responses were investigated in retinotopically-defined regions V1, V2 and V3 and then over the acquired cortical volume. Relative to matched control subjects, patients with NF1 showed deficient activation of the low-level visual cortex to both stimulus types. Importantly, this finding was observed for children and adults with NF1, indicating that low-level visual processing deficits do not ameliorate with age. Moreover, only during M-biased stimulation patients with NF1 failed to deactivate or even activated anterior and posterior midline regions of the default mode network. The observation that the magnocellular visual pathway is impaired in NF1 in early visual processing and is specifically associated with a deficient deactivation of the default mode network may provide a neural explanation for high-order cognitive deficits present in NF1, particularly visuospatial and attentional. A link between magnocellular and default mode network processing may generalize to neuropsychiatric disorders where such deficits have been separately identified.
Highlights
Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder, with an incidence of 1 in 3500 individuals [1] and one of the most common autosomal dominant genetic disorders affecting the human nervous system
Behaviour There was no between group differences on the performance in the behavioural task, neither for children nor for adults clinical groups. Both NF1 patients and controls responded to the fixation task, which imposed a moderate attentional load, with a high degree of accuracy and low number of false alarms
Activity in Retinotopically Defined Areas The magnitude of activation elicited by the M- and P-biased stimuli was retrieved from low-level visual areas V1, V2d, V2v, V3d and V3v of each subject’s hemispheres
Summary
Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder, with an incidence of 1 in 3500 individuals [1] and one of the most common autosomal dominant genetic disorders affecting the human nervous system. It is caused by mutations in a single gene (NF1) and constitutes a valuable model for understanding genetic, neurochemical and brain-behaviour relationships. The hallmark cognitive deficit of the disorder is visuospatial impairment [6,7], for which a number of studies have provided behavioural ([5,8] see [9,10] for review) and functional magnetic resonance imaging (fMRI) [8,9] evidences.
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