Biology subjects

Buckner, R. L.

Publications and source records attributed to Buckner, R. L..

26 records · Page 2Linked to original sources

bioRxiv2020

The Detailed Organization of the Human Cerebellum Estimated by Intrinsic Functional Connectivity Within the Individual

Distinct regions of the cerebellum connect to separate regions of the cerebral cortex forming a complex topography. While key properties of cerebellar organization have been revealed in group-averaged data, in-depth study of individuals provides an opportunity to discover functional-anatomical features that emerge at a higher spatial resolution. Here functional connectivity MRI was used to examine the cerebellum of two intensively-sampled individuals (each scanned across 31 MRI sessions). Connectivity to somatomotor cortex showed the expected crossed laterality and inversion of the body maps between the anterior and posterior lobes. A surprising discovery was connectivity to the primary visual cortex along the vermis with evidence for representation of the central field. Within the hemispheres, each individual displayed a hierarchical progression from the inverted anterior lobe somatomotor map through to higher-order association zones. The hierarchy ended near Crus I/II and then progressed in reverse order through to the upright somatomotor map in the posterior lobe. Evidence for a third set of networks was found in the most posterior extent of the cerebellum. Detailed analysis of the higher-order association networks around the Crus I/II apex revealed robust representations of two distinct networks linked to the default network, multiple networks linked to cognitive control, as well as a separate representation of a language network. While idiosyncratic spatial details emerged between subjects, each of these networks could be detected in both individuals, and small seed regions placed within the cerebellum recapitulated the full extent of the spatially-specific cerebral networks. The observation of multiple networks in juxtaposed regions at the Crus I/II apex confirms the importance of this zone to higher-order cognitive function and reveals new organizational details.

neuroscience↗

bioRxiv2020

Cortical Thickness Trajectories across the Lifespan: Data from 17,075 healthy individuals aged 3-90 years

Delineating age-related cortical trajectories in healthy individuals is critical given the association of cortical thickness with cognition and behaviour. Previous research has shown that deriving robust estimates of age-related brain morphometric changes requires large-scale studies. In response, we conducted a large-scale analysis of cortical thickness in 17,075 individuals aged 3-90 years by pooling data through the Lifespan Working group of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Consortium. We used fractional polynomial (FP) regression to characterize age-related trajectories in cortical thickness, and we computed normalized growth centiles using the parametric Lambda, Mu, and Sigma (LMS) method. Inter-individual variability was estimated using meta-analysis and one-way analysis of variance. Overall, cortical thickness peaked in childhood and had a steep decrease during the first 2-3 decades of life; thereafter, it showed a gradual monotonic decrease which was steeper in men than in women particularly in middle-life. Notable exceptions to this general pattern were entorhinal, temporopolar and anterior cingulate cortices. Inter-individual variability was largest in temporal and frontal regions across the lifespan. Age and its FP combinations explained up to 59% variance in cortical thickness. These results reconcile uncertainties about age-related trajectories of cortical thickness; the centile values provide estimates of normative variance in cortical thickness, and may assist in detecting abnormal deviations in cortical thickness, and associated behavioural, cognitive and clinical outcomes.

neuroscience↗

bioRxiv2020

Subcortical Volume Trajectories across the Lifespan: Data from 18,605 healthy individuals aged 3-90 years

Age has a major effect on brain volume. However, the normative studies available are constrained by small sample sizes, restricted age coverage and significant methodological variability. These limitations introduce inconsistencies and may obscure or distort the lifespan trajectories of brain morphometry. In response, we capitalised on the resources of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Consortium to examine the age-related morphometric trajectories of the ventricles, the basal ganglia (caudate, putamen, pallidum, and nucleus accumbens), the thalamus, hippocampus and amygdala using magnetic resonance imaging data obtained from 18,605 individuals aged 3-90 years. All subcortical structure volumes were at their maximum early in life; the volume of the basal ganglia showed a gradual monotonic decline thereafter while the volumes of the thalamus, amygdala and the hippocampus remained largely stable (with some degree of decline in thalamus) until the sixth decade of life followed by a steep decline thereafter. The lateral ventricles showed a trajectory of continuous enlargement throughout the lifespan. Significant age-related increase in inter-individual variability was found for the hippocampus and amygdala and the lateral ventricles. These results were robust to potential confounders and could be used to derive risk predictions for the early identification of diverse clinical phenotypes.

neuroscience↗

bioRxiv2019

Situating the Left-Lateralized Language Network in the Broader Organization of Multiple Specialized Large-Scale Distributed Networks

Using procedures optimized to explore network organization within the individual, the topography of a candidate language network was characterized and situated within the broader context of adjacent networks. The candidate network was first identified using functional connectivity and replicated across individuals, datasets, acquisition tasks, and analytic methods. In addition to classical language regions near to perisylvian cortex and temporal pole, additional regions were observed in dorsal posterior cingulate, midcingulate, anterior superior frontal and inferior temporal cortex. The candidate network was selectively activated when processing meaningful (as contrast to non-word) sentences, while spatially adjacent networks showed minimal or even decreased activity. Examined in relation to adjacent networks, the topography of the language network was found to parallel the motif of other association networks including the transmodal association networks linked to theory of mind and episodic remembering (often collectively called the default network). The several networks contained juxtaposed regions in multiple association zones. Outside of these juxtaposed higher-order networks, we further noted a distinct frontotemporal network situated between language regions and a frontal orofacial motor region and a temporal auditory region. A possibility is that these functionally-related sensorimotor regions might anchor specialization of neighboring association regions that develop into the language network. What is most striking is that the canonical language network appears to be just one of multiple similarly organized, differentially specialized distributed networks that populate the evolutionarily expanded zones of human association cortex.

neuroscience↗

bioRxiv2019

Parallel Distributed Networks Dissociate Episodic and Social Functions Within the Individual

Association cortex is organized into large-scale distributed networks. One such network, the default network (DN), is linked to diverse forms of internal mentation, opening debate about whether shared anatomy supports multiple forms of cognition. Alternatively, subtle distinctions in cortical organization could remain to be resolved. Using within-individual analysis procedures that preserve idiosyncratic details of cortical anatomy, we probed whether multiple tasks from two domains - Episodic Projection and Theory of Mind (ToM) - rely upon the same or distinct networks. In an initial experiment (n=6, subjects scanned 4 times each), we found evidence that Episodic Projection and ToM tasks activate distinct functional regions distributed throughout cortex, with adjacent regions in parietal, temporal, prefrontal and midline zones. These distinctions were predicted by the hypothesis that the DN comprises two parallel, interdigitated networks. One network, linked to parahippocampal cortex (PHC), is preferentially recruited during Episodic Projection, including both remembering the past and imagining the future. A second juxtaposed network, which includes the temporoparietal junction (TPJ), is differentially engaged during multiple forms of ToM tasks. The TPJ-linked network is interwoven with the PHC-linked network in multiple zones, including the posterior and anterior midline, making clear why it is difficult to fully resolve the two networks in group-averaged or lower-resolution data. We replicated all aspects of this network dissociation in a second, prospectively acquired dataset (n=6). These results refine our understanding of the functional-anatomical organization of association cortex as well as raise questions about how functional specialization might arise in parallel, juxtaposed association networks.

neuroscience↗

bioRxiv2019

Precision Brain Morphometry: Feasibility and Opportunities of Extreme Rapid Scans

The traditional approach to achieve optimal structural brain morphometry is to increase spatial resolution and maintain a high signal-to-noise ratio within a single scanning session using long acquisitions. Here we explore alternative approaches that use multiple rapid structural scans and averaging to achieve stable morphometric estimates. Effects of sequence, resolution, acceleration, and number of scans within- and between-sessions were varied across six studies that included 1,025 scans. Single ~1-min magnetization-prepared rapid gradient echo (MP-RAGE) scans that use wave-controlled aliasing in parallel imaging (Wave-CAIPI) encoding yield morphometric estimates nearly as accurate as those obtained with traditional long scans. Averaging estimates from multiple rapid scans reduces error below traditional approaches using less total acquisition time. Test-retest reliability within- and between-sessions for ~2 min multi-echo MP-RAGE scans revealed that a source of error is the idiosyncratic positioning of the subject's head between sessions. Cluster scanning over multiple tightly-spaced sessions mitigates this effect and achieves cortical thickness estimates with less than 10m global (30m regional) error. Test-retest error for the hippocampus falls below 0.6%. Additional sources of error include coil heating when scans are acquired rapidly within the same session and change in console software between sessions. Rapid acquisitions allow novel experimental designs that can use cluster scanning to achieve precise longitudinal assessment within the individual, build in robustness by affording redundant acquisitions, and reduce the structural scanning burden to a minute when anatomical registration is the goal. The field should consider replacing long structural scans with fast alternatives.

neuroscience↗

bioRxiv2018

Parallel Distributed Networks Resolved at High Resolution Reveal Close Juxtaposition of Distinct Regions

Examination of large-scale distributed networks within the individual reveals details of cortical network organization that are absent in group-averaged studies. One recent discovery is that a distributed transmodal network, often referred to as the default network, is comprised of two separate but closely interdigitated networks, only one of which is coupled to posterior parahippocampal cortex. Not all studies of individuals have identified the same networks and questions remain about the degree to which the two networks are separate, particularly within regions hypothesized to be interconnected hubs. Here we replicate the observation of network separation across analytical (seed-based connectivity and parcellation) and data projection (volume and surface) methods in 2 individuals each scanned 31 times. Additionally, 3 individuals were examined with high-resolution fMRI to gain further insight into the anatomical details. The two networks were identified with separate regions localized to adjacent portions of the cortical ribbon, sometimes inside the same sulcus. Midline regions previously implicated as hubs revealed near complete spatial separation of the two networks, displaying a complex spatial topography in the posterior cingulate and precuneus. The network coupled to parahippocampal cortex also revealed a separate region directly within the hippocampus at or near the subiculum. These collective results support that the default network is composed of at least two spatially juxtaposed networks. Fine spatial details and juxta-positions of the two networks can be identified within individuals at high resolution, providing insight into the network organization of association cortex and placing further constraints on interpretation of group-averaged neuroimaging data.

neuroscience↗

bioRxiv2018

Macroscale Cortical Organization and a Default-Like Transmodal Apex Network in the Marmoset Monkey

Networks of widely distributed regions populate human association cortex. One network, often called the default network, is positioned at the apex of a gradient of sequential networks that radiate outward from primary cortex. Here extensive anatomical data made available through the Marmoset Brain Architecture Project were explored to determine if a homologue exists in marmoset. Results revealed that a gradient of networks extend outward from primary cortex to progressively higher-order transmodal association cortex in both frontal and temporal cortex. The transmodal apex network comprises frontopolar and rostral temporal association cortex, parahippocampal areas TH / TF, the ventral posterior midline, and lateral parietal association cortex. The positioning of this network in the gradient and its composition of areas make it a candidate homologue to the human default network. That the marmoset, a physiologically- and genetically-accessible primate, might possess a default-network-like candidate creates opportunities for study of higher cognitive and social functions.

neuroscience↗