Cortical Terminations of the Inferior Fronto-Occipital and Uncinate Fasciculi: Anatomical Stem-Based Virtual Dissection.

We combined the neuroanatomists' approach of defining a fascicle as all fibers passing through its compact stem with diffusion-weighted tractography to investigate the cortical terminations of two association tracts, the inferior fronto-occipital fasciculus (IFOF) and the uncinate fasciculus (UF), which have recently been implicated in the ventral language circuitry. The aim was to provide a detailed and quantitative description of their terminations in 60 healthy subjects and to do so to apply an anatomical stem-based virtual dissection, mimicking classical post-mortem dissection, to extract with minimal a priori the IFOF and UF from tractography datasets. In both tracts, we consistently observed more extensive termination territories than their conventional definitions, within the middle and superior frontal, superior parietal and angular gyri for the IFOF and the middle frontal gyrus and superior, middle and inferior temporal gyri beyond the temporal pole for the UF. We revealed new insights regarding the internal organization of these tracts by investigating for the first time the frequency, distribution and hemispheric asymmetry of their terminations. Interestingly, we observed a dissociation between the lateral right-lateralized and medial left-lateralized fronto-occipital branches of the IFOF. In the UF, we observed a rightward lateralization of the orbito-frontal and temporal branches. We revealed a more detailed map of the terminations of these fiber pathways that will enable greater specificity for correlating with diseased populations and other behavioral measures. The limitations of the diffusion tensor model in this study are also discussed. We conclude that anatomical stem-based virtual dissection with diffusion tractography is a fruitful method for studying the structural anatomy of the human white matter pathways.

Planum temporale asymmetry and models of dominance for language: a reappraisal.

A classical developmental model for the left hemisphere specialization for language has been proposed based on the observation of a positive correlation coefficient between the value of an index of asymmetry between the left and right planum temporale surface areas and the size of the right planum temporale. Here, we demonstrate that such correlation is a mathematical artefact and thus should not serve as a basis for establishing models of language hemispheric dominance.

Plasma long-chain omega-3 fatty acids and atrophy of the medial temporal lobe.

OBJECTIVE: The long-chain ω-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are potential candidates for interventions to delay Alzheimer disease (AD), but evidence from clinical studies is mixed. We aimed at determining whether plasma levels of EPA or DHA predict atrophy of medial temporal lobe (MTL) gray matter regions in older subjects. METHODS: A total of 281 community dwellers from the Three-City Study, aged 65 years or older, had plasma fatty acid measurements at baseline and underwent MRI examinations at baseline and at 4 years. We studied the association between plasma EPA and DHA and MTL gray matter volume change at 4 years. RESULTS: Higher plasma EPA, but not DHA, was associated with lower gray matter atrophy of the right hippocampal/parahippocampal area and of the right amygdala (p < 0.05, familywise error corrected). Based on a mean right amygdala volume loss of 6.0 mm(3)/y (0.6%), a 1 SD higher plasma EPA (+0.64% of total plasma fatty acids) at baseline was related to a 1.3 mm(3) smaller gray matter loss per year in the right amygdala. Higher atrophy of the right amygdala was associated with greater 4-year decline in semantic memory performances and more depressive symptoms. CONCLUSION: The amygdala, which develops neuropathology in the early stage of AD and is involved in the pathogenesis of depression, may be an important brain structure involved in the association between EPA and cognitive decline and depressive symptoms.

Comparison of spatial normalization procedures and their impact on functional maps.

The alignment accuracy and impact on functional maps of four spatial normalization procedures have been compared using a set of high resolution brain MRIs and functional PET volumes acquired in 20 subjects. Simple affine (AFF), fifth order polynomial warp (WRP), discrete cosine basis functions (SPM), and a movement model based on full multi grid (FMG) approaches were applied on the same dataset for warping individual volumes onto the Human Brain Atlas (HBA) template. Intersubject averaged structural volumes and tissue probability maps were compared across normalization methods and to the standard brain. Thanks to the large number of degrees of freedom of the technique, FMG was found to provide enhanced alignment accuracy as compared to the other three methods, both for the grey and white matter tissues; WRP and SPM exhibited very similar performances whereas AFF had the lowest registration accuracy. SPM, however, was found to perform better than the other methods for the intra-cerebral cerebrospinal fluid (mainly in the ventricular compartments). Limited differences in terms of activation morphology and detection sensitivity were found between low resolution functional maps (FWHM approximately 10 mm) spatially normalized with the four methods, which overlapped in 42.8% of the total activation volume. These findings suggest that the functional variability is much larger than the anatomical one and that precise alignment of anatomical features has low influence on the resulting intersubject functional maps. When increasing the spatial resolution to approximately 6 mm, however, differences in localization of activated areas appear as a consequence of the different spatial normalization procedure used, restricting the overlap of the normalized activated volumes to only 6.2%.