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Abstract:
The macaque monkey has been an important model for understanding human vision. A substantial literature compares human and macaque functional cortical responses to visual stimuli in order to better understand cellular mechanisms from macaque studies (Tootell et al. 2003; Wandell and Winawer 2011; Vanduffel et al. 2014). The anatomical connections in the white matter are another important source for clarifying the similarities and differences between human and macaque cortex. Recent progress on diffusion MRI and tractography enables us to identify major white matter pathways from human brains (Catani et al. 2002; Schmahmann et al. 2007; Wandell 2016). This study compares the organization of major occipital
white matter tracts in human and macaque. We analyzed diffusion MRI data, collected from 4 macaques and 10 humans using the Ensemble Tractography method (Takemura et al., 2016). We identified 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. Then we focused
on the macaque VOF, which has been little studied (Yeatman et al., 2014). The estimated macaque VOF position is consistent with classical invasive anatomical studies by Wernicke. The homology of human and macaque VOF is supported because the endpoints are near similar maps (V3A and ventral V4) between human and macaque. However, the macaque VOF fibers intertwine with the dorsal segment of the ILF, while the human VOF are relatively 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.
