Bio

Bio


Rodrigo trained with Robert Leech and Richard Wise at Imperial College London, where he obtained his Ph.D. investigating the neural systems involved in top-down attention to auditory and visual modalities. Rodrigo was awarded a Sir Henry Wellcome Postdoctoral Fellowship to travel to Harvard University to work with Randy Buckner. There he developed methods to characterize functional networks within individuals and using high-resolution mapping techniques at high-magnetic-strength 7T MRI. Rodrigo holds a K99 Pathway to Independence Award from the National Institute of Health, and currently works with Josef Parvizi and Russ Poldrack.

Rodrigo?s research aims to understand the function and physiology of the distributed networks that occupy association cortex. A long-standing hypothesis is that these large-scale networks are specialized and interact to enable different cognitive processes. Revealing the nature of these specializations requires functional imaging to be conducted with enough precision to resolve functional zones that are finely juxtaposed and interdigitated along the complex geometry of the cortical surface. Rodrigo uses dense-sampling fMRI techniques that can delineate functional anatomy with precision within individuals. At Stanford, Rodrigo is combining fMRI network mapping with intracranial methods that can reveal the electrophysiological basis of the distributed networks, including how network regions interact to form networks, and how different networks interact to perform cognitive functions.

Academic Appointments


Honors & Awards


  • Pathway to Independence Award (K99/R00), NIH (08/2018 - 07/2020)
  • Sir Henry Wellcome Postdoctoral Fellowship, Wellcome Trust (10/2014 - 07/2018)
  • 3.5-yr PhD Scholarship, UK Medical Research Council (10/2010 - 04/2014)
  • Master of Research Scholarship, UK Medical Research Council (10/2009 - 10/2010)

Publications

All Publications


  • Parallel distributed networks resolved at high resolution reveal close juxtaposition of distinct regions JOURNAL OF NEUROPHYSIOLOGY Braga, R. M., Van Dijk, K. A., Polimeni, J. R., Eldaief, M. C., Buckner, R. L. 2019; 121 (4): 1513?34

    Abstract

    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," comprises two 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. In this study we replicate the observation of network separation across analytical (seed-based connectivity and parcellation) and data projection (volume and surface) methods in two individuals each scanned 31 times. Additionally, three individuals were examined with high-resolution (7T; 1.35 mm) functional magnetic resonance imaging 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 juxtapositions 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. NEW & NOTEWORTHY Recent evidence has emerged that canonical large-scale networks such as the "default network" fractionate into parallel distributed networks when defined within individuals. This research uses high-resolution imaging to show that the networks possess juxtapositions sometimes evident inside the same sulcus and within regions that have been previously hypothesized to be network hubs. Distinct circumscribed regions of one network were also resolved in the hippocampal formation, at or near the parahippocampal cortex and subiculum.

    View details for DOI 10.1152/jn.00808.2018

    View details for Web of Science ID 000465083500034

    View details for PubMedID 30785825

    View details for PubMedCentralID PMC6485740

  • Parallel Interdigitated Distributed Networks within the Individual Estimated by Intrinsic Functional Connectivity NEURON Braga, R. M., Buckner, R. L. 2017; 95 (2): 457-+

    Abstract

    Certain organizational features of brain networks present in the individual are lost when central tendencies are examined in the group. Here we investigated the detailed network organization of four individuals each scanned 24 times using MRI. We discovered that the distributed network known as the default network is comprised of two separate networks possessing adjacent regions in eight or more cortical zones. A distinction between the networks is that one is coupled to the hippocampal formation while the other is not. Further exploration revealed that these two networks were juxtaposed with additional networks that themselves fractionate group-defined networks. The collective networks display a repeating spatial progression in multiple cortical zones, suggesting that they are embedded within a broad macroscale gradient. Regions contributing to the newly defined networks are spatially variable across individuals and adjacent to distinct networks, raising issues for network estimation in group-averaged data and applied endeavors, including targeted neuromodulation.

    View details for DOI 10.1016/j.neuron.2017.06.038

    View details for Web of Science ID 000405857500021

    View details for PubMedID 28728026

    View details for PubMedCentralID PMC5519493

  • Echoes of the Brain within Default Mode, Association, and Heteromodal Cortices JOURNAL OF NEUROSCIENCE Braga, R. M., Sharp, D. J., Leeson, C., Wise, R. S., Leech, R. 2013; 33 (35): 14031?39

    Abstract

    Intrinsic connectivity networks (ICNs), such as the default mode, frontoparietal control, and salience networks, provide a useful large-scale description of the functional architecture of the brain. Although ICNs are functionally specialized, the information that they process needs to be integrated for coherent cognition, perception, and behavior. A region capable of performing this integration might be expected to contain traces, or "echoes," of the neural signals from multiple ICNs. Here, using fMRI in humans, we show the existence of specific "transmodal" regions containing echoes of multiple ICNs. These regions include core nodes of the default mode network, as well as multimodal association regions of the temporoparietal and temporo-occipito-parietal junction, right middle frontal gyrus, and dorsal anterior cingulate cortex. In contrast, "unimodal" regions such as the primary sensory and motor cortices show a much more singular pattern of activity, containing traces of few or even single ICNs. The presence of ICN echoes might explain how transmodal regions are involved in multiple different cognitive states. Our results suggest that these transmodal regions have a particular local spatial organization containing topographic maps that relate to multiple ICNs. This makes transmodal regions uniquely placed to be able to mediate the cross talk between the brain's functional networks through local modulation of adjacent regions that communicate with different ICNs.

    View details for DOI 10.1523/JNEUROSCI.0570-13.2013

    View details for Web of Science ID 000323727000011

    View details for PubMedID 23986239

    View details for PubMedCentralID PMC3810536

  • Echoes of the Brain within the Posterior Cingulate Cortex JOURNAL OF NEUROSCIENCE Leech, R., Braga, R., Sharp, D. J. 2012; 32 (1): 215?22

    Abstract

    There is considerable uncertainty about the function of the posterior cingulate cortex (PCC). The PCC is a major node within the default mode network (DMN) and has high metabolic activity and dense structural connectivity to widespread brain regions, which suggests it has a role as a cortical hub. The region appears to be involved in internally directed thought, for example, memory recollection. However, recent nonhuman primate work provides evidence for a more active role in the control of cognition, through signaling an environmental change and the need to alter behavior. For an organism to flexibly react to a changing environment, information processed in functionally distinct brain networks needs to be integrated by such a cortical hub. If the PCC is involved in this process, its brain activity should show a complex and dynamic pattern that partially reflects activity in other brain networks. Using fMRI in humans and a multivariate analysis, we demonstrate that the PCC shows this type of complex functional architecture, where echoes of multiple other brain networks are seen in separable yet overlapping subregions. For example, a predominantly ventral region shows strong functional connectivity to the rest of the DMN, whereas two subregions within the dorsal PCC show high connectivity to frontoparietal networks involved in cognitive control. PCC subregions showed distinct patterns of activity modulation during the performance of an attentionally demanding task, suggesting that parts of the dorsal PCC interact with frontoparietal networks to regulate the balance between internally and externally directed cognition.

    View details for DOI 10.1523/JNEUROSCI.3689-11.2012

    View details for Web of Science ID 000299119700020

    View details for PubMedID 22219283

    View details for PubMedCentralID PMC6621313

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