Fine-Grained Parcellation of the Macaque Nucleus Accumbens by High-Resolution Diffusion Tensor Tractography

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.

The ventral striatum dissociates information expectation, reward anticipation, and reward receipt

“…Our medial-lateral subdivision of the VS is in line with recent macaque ex vivo highresolution diffusion tensor MRI findings (42), which demonstrated that the VS contains medial, lateral, ventral, and dorsal subdivisions. Whereas the medial tractography-based subdivision corresponds well to the histological NAcc, the lateral tractographybased VS region corresponds to the histological "neurochemically unique domains of the accumbens and putamen (NUDAPs)," which show a unique pattern of u-and k-opioid as well as D1-like dopamine receptors (42). This tractography-based medial-lateral distinction in the macaque matches our fMRI activations, suggesting a lateral VS-NAcc subdivision in humans.…”

“…Anatomically, the VS is heterogeneous, with differences between subregions such as the core and shell (12), and different activation patterns depending on which limbic and cortical inputs are integrated in different contexts (5). Our medial-lateral subdivision of the VS is in line with recent macaque ex vivo highresolution diffusion tensor MRI findings (42), which demonstrated that the VS contains medial, lateral, ventral, and dorsal subdivisions. Whereas the medial tractography-based subdivision corresponds well to the histological NAcc, the lateral tractographybased VS region corresponds to the histological "neurochemically unique domains of the accumbens and putamen (NUDAPs)," which show a unique pattern of u-and k-opioid as well as D1-like dopamine receptors (42).…”

Fine-Grained Topography and Modularity of the Macaque Frontal Pole Cortex Revealed by Anatomical Connectivity Profiles

“…Second, to some extent, challenges were raised in CBP studies because of the inter-individual variability, which made it difficult to relate the anatomical connectivity patterns of a region to its functional roles [29]. Third, in this study, the efficiency of the parcellation framework based on CBP and the parameters for parcellation have been validated by many studies [33,43,48,92]. In general, it is worth noting that all the parameters must be reasonable, which means that they cannot be uncommon extreme values, otherwise wrong results will be tracked.…”

“…However, in the current study, we mainly set two parameters (number of samples = 15000; step size = 0.2 mm), other parameters are based on the default values. All these parameters were based on previous studies [33,42] and the official instructions of FSL. Tournier et al have revealed that the dispersion in tractography is dependent on the step size; small step sizes reduce the spread of probabilistic tracking results [98].…”

Mapping Connectional Differences between Humans and Macaques in the Nucleus Accumbens Shell-Core Architecture

“…3A) and low-resolution in vivo (Fig. 3B) macaque MRI datasets showed that the Acb can be subdivided into ventromedial and dorsolateral regions based on whole-brain voxel-wise tractography (Xia et al, 2019b).…”