Neuroanatomical correlates of working memory performance in Neurofibromatosis 1

Background: Neurofibromatosis 1 (NF1) is a single-gene neurodevelopmental disorder associated with cognitive and behavioural impairments, particularly with deficits in working memory. This study investigates the cerebral volumetric differences in adolescents with NF1 as compared to typically developing controls and how working memory task performance is associated with these differences. Methods: 31 adolescents aged 11-17 years were compared to age and sex-matched controls. NF1 subjects were assessed using detailed multimodal measurement of working memory at baseline followed by a 3T MR scan. A voxel-based morphometry approach was used to estimate the total and regional gray matter(GM) volumetric differences between the NF1 and control groups. The working memory metrics were subjected to a principal component analysis (PCA) approach. Finally, we examined how the components derived from PCA correlated with the changes in GM volume in the NF1 group, after adjusting for age, sex and total intracranial volume. Results: The NF1 cohort showed increased GM volumes in the thalamus, globus pallidus, caudate, putamen, dorsal midbrain and cerebellum bilaterally as compared to controls. The PCA yielded three independent behavioural components reflecting high memory load, low memory load and auditory working memory. Correlation analyses revealed that increased volume of the inferior lateral parietal cortex was associated with poorer performance on the high working memory load tasks. Increased volume of posterior cingulate cortex, a key component of the default mode network (DMN) was significantly associated with poorer performance on low working memory load tasks. Discussion: This is the first study to examine the neuroanatomical correlates of working memory in NF1 adolescents. Consistent with prior literature we show larger subcortical brain volumes in in the NF1 cohort. The strong association between posterior cingulate cortex volume and performance on low memory load conditions supports previously suggested hypotheses of deficient DMN structural development, which in turn may contribute to the cognitive impairments in NF1.