Abstract
Limited in part by the spatial resolution of typical in vivo magnetic resonance imaging (MRI) data, recent neuroimaging studies have only identified a connectivity-based shell-core-like partitioning of the nucleus accumbens (Acb) in humans. This has hindered the process of making a more refined description of the Acb using non-invasive neuroimaging technologies and approaches. In this study, high-resolution ex vivo macaque brain diffusion MRI data were acquired to investigate the tractography-based parcellation of the Acb. Our results identified a shell-core-like partitioning in macaques that is similar to that in humans as well as an alternative solution that subdivided the Acb into four parcels, the medial shell, the lateral shell, the ventral core, and the dorsal core. Furthermore, we characterized the specific anatomical and functional connectivity profiles of these Acb subregions and generalized their specialized functions to establish a fine-grained macaque Acb brainnetome atlas. This atlas should be helpful in neuroimaging, stereotactic surgery, and comparative neuroimaging studies to reveal the neurophysiological substrates of various diseases and cognitive functions associated with the Acb.
Highlights
The nucleus accumbens (Acb) is an integral part of the striatal complex (Heimer et al, 1991) and exhibits multi-aspect and multi-level heterogeneity (Meredith et al, 1996; Humphries and Prescott, 2010)
The striatum was recursively parcellated based on probabilistic diffusion tractography to generate a relatively accurate connectivity-based Acb region
We named this striatal subregion as the ventral striatum-like division for its good correspondence with the anatomically- described ventral striatum, comprising the Acb, the broad continuity between the caudate nucleus and putamen ventral to the rostral internal capsule, the olfactory tubercle (Heimer et al, 1999), and the medial caudate nucleus from a connectional perspective (Haber and McFarland, 1999)
Summary
The nucleus accumbens (Acb) is an integral part of the striatal complex (Heimer et al, 1991) and exhibits multi-aspect (e.g., connectivity and function) and multi-level (from macro- to micro-level) heterogeneity (Meredith et al, 1996; Humphries and Prescott, 2010). The Acb cannot be directly delineated by magnetic resonance imaging (MRI) due to a lack of distinct signal intensity, but human Acb-like regions have been identified using connectivitybased parcellations of the striatum (Tziortzi et al, 2013; Janssen et al, 2015; Fan et al, 2016). These connectivity-defined regions appeared to have significant extensions into the caudate nucleus and putamen compared to the microanatomical-defined Acb and are better suited to be considered as a ventral striatum-like or limbic striatum-like region. Identifying this will enable researchers to perform connection analyses in a reasonable fashion, e.g., tractography-based parcellation (Eickhoff et al, 2015)
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