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Understanding the similarity of cortico-subcortical networks topologies between humans and nonhuman primate species is critical to study the origin of network alternations underlying human neurologic and neuropsychiatric diseases. The New World common marmoset ( Callithrix jacchus ) has become popular as a nonhuman primate model for human brain function. Most marmoset connectomic research, however, has exclusively focused on cortical areas, with connectivity to subcortical networks less extensively explored. Here, we aimed to first isolate patterns of subcortical connectivity with cortical resting-state networks in awake marmosets using resting-state fMRI, then to compare these networks with those in humans using connectivity fingerprinting. In this study, we used 5 marmosets (4 males, 1 female). While we could match several marmoset and human resting-state networks based on their functional fingerprints, we also found a few striking differences, for example, strong functional connectivity of the default mode network with the superior colliculus in marmosets that was much weaker in humans. Together, these findings demonstrate that many of the core cortico-subcortical networks in humans are also present in marmosets, but that small, potentially functionally relevant differences exist. SIGNIFICANCE STATEMENT The common marmoset is becoming increasingly popular as an additional preclinical nonhuman primate model for human brain function. Here we compared the functional organization of cortico-subcortical networks in marmosets and humans using ultra-high field fMRI. We isolated the patterns of subcortical connectivity with cortical resting-state networks (RSNs) in awake marmosets using resting-state fMRI and then compared these networks with those in humans using connectivity fingerprinting. While we could match several marmoset and human RSNs based on their functional fingerprints, we also found several striking differences. Together, these findings demonstrate that many of the core cortico-subcortical RSNs in humans are also present in marmosets, but that small, potentially functionally relevant differences exist., (Copyright © 2020 the authors.)

Reconstructing the anatomical pathways of the brain to study the human connectome has become an important endeavour for understanding brain function and dynamics. Reconstruction of the cortico-cortical connectivity matrix in vivo often relies on noninvasive diffusion-weighted imaging (DWI) techniques but the extent to which they can accurately represent the topological characteristics of structural connectomes remains unknown. We addressed this question by constructing connectomes using DWI data collected from macaque monkeys in vivo and with data from published invasive tracer studies. We found the strength of fiber tracts was well estimated from DWI and topological properties like degree and modularity were captured by tractography-based connectomes. Rich-club/core-periphery type architecture could also be detected but the classification of hubs using betweenness centrality, participation coefficient and core-periphery identification techniques was inaccurate. Our findings indicate that certain aspects of cortical topology can be faithfully represented in noninvasively-obtained connectomes while other network analytic measures warrant cautionary interpretations., (Copyright © 2019 Elsevier Inc. All rights reserved.)

It has been previously shown that small- and large-amplitude saccades have different functions during vision in natural environments. Large saccades are associated with reaching movements toward objects, whereas small saccades facilitate the identification of more detailed object features necessary for successful grasping and manual manipulation. To determine whether these represent dichotomous processing streams, we used resting-state functional MRI to examine the functional connectivity patterns of the medial and lateral frontal eye field (FEF) regions that encode large- and small-amplitude saccades, respectively. We found that the spontaneous blood oxygen level-dependent signals of the medial FEF were functionally correlated with areas known to be involved in reaching movements and executive control processes, whereas lateral FEF was functionally correlated with cortical areas involved in object processing and in grasping, fixation, and manipulation of objects. The results provide strong evidence for two distinct visuomotor network systems in the primate brain that likely reflect the alternating phases of vision for action in natural environments.

Computational and empirical neuroimaging studies have suggested that the anatomical connections between brain regions primarily constrain their functional interactions. Given that the large-scale organization of functional networks is determined by the temporal relationships between brain regions, the structural limitations may extend to the global characteristics of functional networks. Here, we explored the extent to which the functional network community structure is determined by the underlying anatomical architecture. We directly compared macaque (Macaca fascicularis) functional connectivity (FC) assessed using spontaneous blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI) to directed anatomical connectivity derived from macaque axonal tract tracing studies. Consistent with previous reports, FC increased with increasing strength of anatomical connection, and FC was also present between regions that had no direct anatomical connection. We observed moderate similarity between the FC of each region and its anatomical connectivity. Notably, anatomical connectivity patterns, as described by structural motifs, were different within and across functional modules: partitioning of the functional network was supported by dense bidirectional anatomical connections within clusters and unidirectional connections between clusters. Together, our data directly demonstrate that the FC patterns observed in resting-state BOLD-fMRI are dictated by the underlying neuroanatomical architecture. Importantly, we show how this architecture contributes to the global organizational principles of both functional specialization and integration.

The purpose of the present study was to determine the cortical structures involved with integrated baroreceptor-mediated modulation of autonomic cardiovascular function in conscious humans independent of changes in arterial blood pressure. We assessed the brain regions associated with lower body negative pressure (LBNP)-induced baroreflex control using functional magnetic resonance imaging with blood oxygen level-dependent (BOLD) contrast in eight healthy male volunteer subjects. The levels of LBNP administered were 5, 15 and 35 mmHg. Heart rate (HR; representing the cardiovascular response) and LBNP (representing the baroreceptor activation level) were simultaneously monitored during the scanning period. In addition, estimated central venous pressure (CVP), arterial blood pressure (ABP) and muscle sympathetic nerve activity were recorded on a separate session. Random effects analyses (SPM2) were used to evaluate significant (P < 0.05) BOLD signal changes that correlated separately with both LBNP and HR (15- and 35-mmHg versus 5-mmHg LBNP). Compared to baseline, steady-state LBNP at 15 and 35 mmHg decreased CVP (from 7 +/- 1 to 5 +/- 1 and 4 +/- 1 mmHg, respectively) and increased MSNA (from 12 +/- 1 to 23 +/- 3 and 36 +/- 4 bursts min(-1), respectively, both P < 0.05 versus baseline). Furthermore, steady-state LBNP elevated HR from 54 +/- 2 beats min(-1) at baseline to 64 +/- 2 beats min(-1) at 35-mmHg suction. Both mean arterial and pulse pressure were not different between rest and any level of LBNP. Cortical regions demonstrating increased activity that correlated with higher HR and greater LBNP included the right superior posterior insula, frontoparietal cortex and the left cerebellum. Conversely, using the identical statistical paradigm, bilateral anterior insular cortices, the right anterior cingulate, orbitofrontal cortex, amygdala, midbrain and mediodorsal nucleus of the thalamus showed decreased neural activation. These data corroborate previous investigations highlighting the involved roles of the insula, anterior cingulate cortex and amygdala in central autonomic cardiovascular control. In addition, we have provided the first evidence for the identification of the cortical network involved specifically with baroreflex-mediated autonomic cardiovascular function in conscious humans.

Brain-imaging studies have shown that visually-cued, voluntary swallowing activates a distributed network of cortical regions including the precentral and postcentral gyri, anterior cingulate cortex (ACC), insula, frontoparietal operculum, cuneus and precuneus. To elucidate the functional contributions of these discrete activation foci for swallowing, a "Go, No-Go" functional magnetic resonance imaging (fMRI) paradigm was designed. Brain activation associated with visually-cued swallowing was compared with brain activation evoked by a comparable visual cue instructing the subject not to swallow. Region-of-interest analyses performed on data from eight healthy subjects showed a significantly greater number of activated voxels within the precentral gyrus, postcentral gyrus, and ACC during the "Go" condition compared to the "No-Go" condition. This finding suggests that the precentral gyrus, postcentral gyrus, and ACC contribute primarily to the act of swallowing. In contrast, the numbers of activated voxels within the cuneus and precuneus were not significantly different for the "Go" and "No-Go" conditions, suggesting that these regions mediate processing of the cue to swallow. Together these findings support the view that the discrete cortical foci previously implicated in swallowing mediate functionally distinct components of the swallowing act.

Background: Neuroanatomical studies investigating the connectivity of brain areas have heretofore employed procedures in which chemical or viral tracers are injected into an area of interest, and connected areas are subsequently identified using histological techniques. Such experiments require the sacrifice of the animals and do not allow for subsequent electrophysiological studies in the same subjects, rendering a direct investigation of the functional properties of anatomically identified areas impossible. Methodology/Principal Findings: Here, we used a combination of microstimulation and fMRI in an anesthetized monkey preparation to study the connectivity of the superior colliculus (SC). Microstimulation of the SC resulted in changes in the blood oxygenation level-dependent (BOLD) signals in the SC and in several cortical and subcortical areas consistent with the known connectivity of the SC in primates. Conclusions/Significance: These findings demonstrates that the concurrent use of microstimulation and fMRI can be used to identify brain networks for further electrophysiological or fMRI investigation. [ABSTRACT FROM AUTHOR]

Although multiple regions of the cerebral cortex have been implicated in swallowing, the functional contributions of each brain area remain unclear. The present study sought to clarify the roles of these cortical foci in swallowing by comparing brain activation associated with voluntary saliva swallowing and voluntary tongue elevation. Fourteen healthy right-handed subjects were examined with single-event-related functional magnetic resonance imaging (fMRI) while laryngeal movements associated with swallowing and tongue movement were simultaneously recorded. Both swallowing and tongue elevation activated 1) the left lateral pericentral and anterior parietal cortex, and 2) the anterior cingulate cortex (ACC) and adjacent supplementary motor area (SMA), suggesting that these brain regions mediate processes shared by swallowing and tongue movement. Tongue elevation activated a larger total volume of cortex than swallowing, with significantly greater activation within the ACC, SMA, right precentral and postcentral gyri, premotor cortex, right putamen, and thalamus. Although a contrast analysis failed to identify activation foci specific to swallowing, superimposed activation maps suggested that the most lateral extent of the left pericentral and anterior parietal cortex, rostral ACC, precuneus, and right parietal operculum/insula were preferentially activated by swallowing. This finding suggests that these brain areas may mediate processes specific to swallowing. Approximately 60% of the subjects showed a strong functional lateralization of the postcentral gyrus toward the left hemisphere for swallowing, whereas 40% showed a similar activation bias for the tongue elevation task. This finding supports the view that the oral sensorimotor cortices within the left and right hemispheres are functionally nonequivalent. [ABSTRACT FROM AUTHOR]