Occipital white matter tracts in human and macaque

Abstract

We compare the major white matter tracts in human and macaque occipital lobe using diffusion MRI. The comparison suggests similarities but also significant differences in spatial arrangement and relative sizes of the tracts. There are several apparently homologous tracts in the two species, including the vertical occipital fasciculus (VOF), optic radiation, forceps major, and inferior longitudinal fasciculus (ILF). There is one large human tract, the inferior fronto-occipital fasciculus, with no corresponding fasciculus in macaque. The macaque VOF is compact and its fibers intertwine with the dorsal segment of the ILF, but the human VOF is much more elongated in the anterior-posterior direction and may be lateral to the ILF. These similarities and differences will be useful in establishing which circuitry in the macaque can serve as an accurate model for human visual cortex. key words: diffusion MRI; white matter; visual cortex; comparative study; vertical occipital fasciculus Third, we describe a difference in the relative position of several, large tracts in the occipital lobe, VOF, ILF, and OR. In both human and macaque, the VOF is clearly located lateral to the OR. However, the macaque VOF intermingles with the dorsal segment of the ILF, while the human VOF is more separated from human ILF in terms of tract position and endpoints. Materials and MethodsThe analyses are based on a diverse set of macaque and human measurements, pooled across several laboratories and public datasets. The datasets have different spatial and angular resolution and image quality. MR data acquisition Macaque diffusion data 1 (subject M1, ex vivo)This dataset was acquired from a post-mortem Macaca mulatta (rhesus macaque monkey) brain using 30-cm magnet bore Bruker 7T scanner at the National Institute of Health. The dMRI data were sampled in 121 directions at a spatial resolution of 250 µm isotropic. The b-value was set to 4800 s/mm 2 and TE was 34 ms. Seven non-diffusion weighted image (b=0) were obtained. These data were analyzed in two previous publications (Thomas et al. 2014;Reveley et al. 2015). Macaque diffusion data 2 (subject M2, in vivo)This dataset was acquired from a living Macaca mulatta (rhesus macaque monkey) brain using a Bruker BIOSPEC 4.7 T vertical bore scanner at Max Planck Institute, Tübingen, Germany. The dMRI data were sampled in 61 different directions at a spatial resolution of 750 µm isotropic. The gradient b-value was 1200 s/mm 2 and TE was 62.65 msec. Seven non-diffusion weighted images (b=0) were acquired at the beginning of the scan. The total imaging time was 6 h 48 min. T1-weighted images at 375 um isotropic resolution were also acquired using a 3D-MDEFT sequence (Lee et al. 1995). Macaque diffusion data 3 (subject M3, ex vivo)This dataset was acquired in a formalin-fixed post-mortem Macaca mulatta (rhesus macaque monkey) brain using a Bruker BIOSPEC 4.7 T vertical bore scanner at Max Planck Institute, Tübingen, Germany. The brain was perfused, removed from the skull, and kept in 4% paraformaldehyde for...

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