Bio

Bio


Russell Wade Chan is a postdoctoral research fellow of Neurology at Stanford University. Dr. Chan received his Bachelor?s degree in Biomedical Engineering and Doctoral degree in Electrical and Electronic Engineering at The University of Hong Kong. His research interest is dissecting brain functional networks using neuromodulation (optogenetics) and neuroimaging (functional MRI) methods.

Honors & Awards


  • Summa Cum Laude Award (top 3% of ~8,000 accepted papers), ISMRM (2015 & 2016)
  • Magna Cum Laude Awards (top 15% of ~8,000 accepted papers), ISMRM (2013 X2)
  • Educational Stipend Award, ISMRM (2012-2014)

Boards, Advisory Committees, Professional Organizations


  • Ad Hoc Reviewer, International Society of Magnetic Resonance in Medicine (2017 - Present)
  • Ad Hoc Reviewer, IEEE Engineering in Medicine and Biology Society (2017 - Present)
  • Trainee Member, ISMRM (2012 - Present)

Professional Education


  • Doctor of Philosophy, University Of Hong Kong (2016)
  • Bachelor of Engineering, University Of Hong Kong (2011)

Publications

All Publications


  • Low-frequency hippocampal-cortical activity drives brain-wide resting-state functional MRI connectivity. Proceedings of the National Academy of Sciences of the United States of America Chan, R. W., Leong, A. T., Ho, L. C., Gao, P. P., Wong, E. C., Dong, C. M., Wang, X., He, J., Chan, Y. S., Lim, L. W., Wu, E. X. 2017; 114 (33): E6972?E6981

    Abstract

    The hippocampus, including the dorsal dentate gyrus (dDG), and cortex engage in bidirectional communication. We propose that low-frequency activity in hippocampal-cortical pathways contributes to brain-wide resting-state connectivity to integrate sensory information. Using optogenetic stimulation and brain-wide fMRI and resting-state fMRI (rsfMRI), we determined the large-scale effects of spatiotemporal-specific downstream propagation of hippocampal activity. Low-frequency (1 Hz), but not high-frequency (40 Hz), stimulation of dDG excitatory neurons evoked robust cortical and subcortical brain-wide fMRI responses. More importantly, it enhanced interhemispheric rsfMRI connectivity in various cortices and hippocampus. Subsequent local field potential recordings revealed an increase in slow oscillations in dorsal hippocampus and visual cortex, interhemispheric visual cortical connectivity, and hippocampal-cortical connectivity. Meanwhile, pharmacological inactivation of dDG neurons decreased interhemispheric rsfMRI connectivity. Functionally, visually evoked fMRI responses in visual regions also increased during and after low-frequency dDG stimulation. Together, our results indicate that low-frequency activity robustly propagates in the dorsal hippocampal-cortical pathway, drives interhemispheric cortical rsfMRI connectivity, and mediates visual processing.

    View details for DOI 10.1073/pnas.1703309114

    View details for PubMedID 28760982

    View details for PubMedCentralID PMC5565425

  • Long-range projections coordinate distributed brain-wide neural activity with a specific spatiotemporal profile PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Leong, A. T., Chan, R. W., Gao, P. P., Chan, Y., Tsia, K. K., Yung, W., Wu, E. X. 2016; 113 (51): E8306-E8315

    Abstract

    One challenge in contemporary neuroscience is to achieve an integrated understanding of the large-scale brain-wide interactions, particularly the spatiotemporal patterns of neural activity that give rise to functions and behavior. At present, little is known about the spatiotemporal properties of long-range neuronal networks. We examined brain-wide neural activity patterns elicited by stimulating ventral posteromedial (VPM) thalamo-cortical excitatory neurons through combined optogenetic stimulation and functional MRI (fMRI). We detected robust optogenetically evoked fMRI activation bilaterally in primary visual, somatosensory, and auditory cortices at low (1 Hz) but not high frequencies (5-40 Hz). Subsequent electrophysiological recordings indicated interactions over long temporal windows across thalamo-cortical, cortico-cortical, and interhemispheric callosal projections at low frequencies. We further observed enhanced visually evoked fMRI activation during and after VPM stimulation in the superior colliculus, indicating that visual processing was subcortically modulated by low-frequency activity originating from VPM. Stimulating posteromedial complex thalamo-cortical excitatory neurons also evoked brain-wide blood-oxygenation-level-dependent activation, although with a distinct spatiotemporal profile. Our results directly demonstrate that low-frequency activity governs large-scale, brain-wide connectivity and interactions through long-range excitatory projections to coordinate the functional integration of remote brain regions. This low-frequency phenomenon contributes to the neural basis of long-range functional connectivity as measured by resting-state fMRI.

    View details for DOI 10.1073/pnas.1616361113

    View details for Web of Science ID 000390044900011

    View details for PubMedID 27930323

    View details for PubMedCentralID PMC5187697

  • Structural and Functional Brain Remodeling during Pregnancy with Diffusion Tensor MRI and Resting-State Functional MRI PLOS ONE Chan, R. W., Ho, L. C., Zhou, I. Y., Gao, P. P., Chan, K. C., Wu, E. X. 2015; 10 (12)

    Abstract

    Although pregnancy-induced hormonal changes have been shown to alter the brain at the neuronal level, the exact effects of pregnancy on brain at the tissue level remain unclear. In this study, diffusion tensor imaging (DTI) and resting-state functional MRI (rsfMRI) were employed to investigate and document the effects of pregnancy on the structure and function of the brain tissues. Fifteen Sprague-Dawley female rats were longitudinally studied at three days before mating (baseline) and seventeen days after mating (G17). G17 is equivalent to the early stage of the third trimester in humans. Seven age-matched nulliparous female rats served as non-pregnant controls and were scanned at the same time-points. For DTI, diffusivity was found to generally increase in the whole brain during pregnancy, indicating structural changes at microscopic levels that facilitated water molecular movement. Regionally, mean diffusivity increased more pronouncedly in the dorsal hippocampus while fractional anisotropy in the dorsal dentate gyrus increased significantly during pregnancy. For rsfMRI, bilateral functional connectivity in the hippocampus increased significantly during pregnancy. Moreover, fractional anisotropy increase in the dentate gyrus appeared to correlate with the bilateral functional connectivity increase in the hippocampus. These findings revealed tissue structural modifications in the whole brain during pregnancy, and that the hippocampus was structurally and functionally remodeled in a more marked manner.

    View details for DOI 10.1371/journal.pone.0144328

    View details for Web of Science ID 000366903500020

    View details for PubMedID 26658306

    View details for PubMedCentralID PMC4675543

  • BOLD fMRI study of ultrahigh frequency encoding in the inferior colliculus NEUROIMAGE Gao, P. P., Zhang, J. W., Chan, R. W., Leong, A. T., Wu, E. X. 2015; 114: 427-437

    Abstract

    Many vertebrates communicate with ultrahigh frequency (UHF) vocalizations to limit auditory detection by predators. The mechanisms underlying the neural encoding of such UHF sounds may provide important insights for understanding neural processing of other complex sounds (e.g. human speeches). In the auditory system, sound frequency is normally encoded topographically as tonotopy, which, however, contains very limited representation of UHFs in many species. Instead, electrophysiological studies suggested that two neural mechanisms, both exploiting the interactions between frequencies, may contribute to UHF processing. Neurons can exhibit excitatory or inhibitory responses to a tone when another UHF tone is presented simultaneously (combination sensitivity). They can also respond to such stimulation if they are tuned to the frequency of the cochlear-generated distortion products of the two tones, e.g. their difference frequency (cochlear distortion). Both mechanisms are present in an early station of the auditory pathway, the midbrain inferior colliculus (IC). Currently, it is unclear how prevalent the two mechanisms are and how they are functionally integrated in encoding UHFs. This study investigated these issues with large-view BOLD fMRI in rat auditory system, particularly the IC. UHF vocalizations (above 40kHz), but not pure tones at similar frequencies (45, 55, 65, 75kHz), evoked robust BOLD responses in multiple auditory nuclei, including the IC, reinforcing the sensitivity of the auditory system to UHFs despite limited representation in tonotopy. Furthermore, BOLD responses were detected in the IC when a pair of UHF pure tones was presented simultaneously (45 & 55kHz, 55 & 65kHz, 45 & 65kHz, 45 & 75kHz). For all four pairs, a cluster of voxels in the ventromedial side always showed the strongest responses, displaying combination sensitivity. Meanwhile, voxels in the dorsolateral side that showed strongest secondary responses to each pair of UHF pure tones also showed the strongest responses to a pure tone at their difference frequency, suggesting that they are sensitive to cochlear distortion. These BOLD fMRI results indicated that combination sensitivity and cochlear distortion are employed by large but spatially distinctive neuron populations in the IC to represent UHFs. Our imaging findings provided insights for understanding sound feature encoding in the early stage of the auditory pathway.

    View details for DOI 10.1016/j.neuroimage.2015.04.007

    View details for Web of Science ID 000355002900038

    View details for PubMedID 25869860

  • In vivo visuotopic brain mapping with manganese-enhanced MRI and resting-state functional connectivity MRI NEUROIMAGE Chan, K. C., Fan, S., Chan, R. W., Cheng, J. S., Zhou, I. Y., Wu, E. X. 2014; 90: 235-245

    Abstract

    The rodents are an increasingly important model for understanding the mechanisms of development, plasticity, functional specialization and disease in the visual system. However, limited tools have been available for assessing the structural and functional connectivity of the visual brain network globally, in vivo and longitudinally. There are also ongoing debates on whether functional brain connectivity directly reflects structural brain connectivity. In this study, we explored the feasibility of manganese-enhanced MRI (MEMRI) via 3 different routes of Mn(2+) administration for visuotopic brain mapping and understanding of physiological transport in normal and visually deprived adult rats. In addition, resting-state functional connectivity MRI (RSfcMRI) was performed to evaluate the intrinsic functional network and structural-functional relationships in the corresponding anatomical visual brain connections traced by MEMRI. Upon intravitreal, subcortical, and intracortical Mn(2+) injection, different topographic and layer-specific Mn enhancement patterns could be revealed in the visual cortex and subcortical visual nuclei along retinal, callosal, cortico-subcortical, transsynaptic and intracortical horizontal connections. Loss of visual input upon monocular enucleation to adult rats appeared to reduce interhemispheric polysynaptic Mn(2+) transfer but not intra- or inter-hemispheric monosynaptic Mn(2+) transport after Mn(2+) injection into visual cortex. In normal adults, both structural and functional connectivity by MEMRI and RSfcMRI was stronger interhemispherically between bilateral primary/secondary visual cortex (V1/V2) transition zones (TZ) than between V1/V2 TZ and other cortical nuclei. Intrahemispherically, structural and functional connectivity was stronger between visual cortex and subcortical visual nuclei than between visual cortex and other subcortical nuclei. The current results demonstrated the sensitivity of MEMRI and RSfcMRI for assessing the neuroarchitecture, neurophysiology and structural-functional relationships of the visual brains in vivo. These may possess great potentials for effective monitoring and understanding of the basic anatomical and functional connections in the visual system during development, plasticity, disease, pharmacological interventions and genetic modifications in future studies.

    View details for DOI 10.1016/j.neuroimage.2013.12.056

    View details for Web of Science ID 000338909500024

    View details for PubMedID 24394694

    View details for PubMedCentralID PMC3951771

  • Resting-State fMRI Using Passband Balanced Steady-State Free Precession PLOS ONE Cheng, J. S., Gao, P. P., Zhou, I. Y., Chan, R. W., Chan, Q., Mak, H. K., Khong, P. L., Wu, E. X. 2014; 9 (3)

    Abstract

    Resting-state functional MRI (rsfMRI) has been increasingly used for understanding brain functional architecture. To date, most rsfMRI studies have exploited blood oxygenation level-dependent (BOLD) contrast using gradient-echo (GE) echo planar imaging (EPI), which can suffer from image distortion and signal dropout due to magnetic susceptibility and inherent long echo time. In this study, the feasibility of passband balanced steady-state free precession (bSSFP) imaging for distortion-free and high-resolution rsfMRI was investigated.rsfMRI was performed in humans at 3 T and in rats at 7 T using bSSFP with short repetition time (TR?=?4/2.5 ms respectively) in comparison with conventional GE-EPI. Resting-state networks (RSNs) were detected using independent component analysis.RSNs derived from bSSFP images were shown to be spatially and spectrally comparable to those derived from GE-EPI images with considerable intra- and inter-subject reproducibility. High-resolution bSSFP images corresponded well to the anatomical images, with RSNs exquisitely co-localized to the gray matter. Furthermore, RSNs at areas of severe susceptibility such as human anterior prefrontal cortex and rat piriform cortex were proved accessible. These findings demonstrated for the first time that passband bSSFP approach can be a promising alternative to GE-EPI for rsfMRI. It offers distortion-free and high-resolution RSNs and is potentially suited for high field studies.

    View details for DOI 10.1371/journal.pone.0091075

    View details for Web of Science ID 000332845300048

    View details for PubMedID 24622278

    View details for PubMedCentralID PMC3951283

  • Brain resting-state functional MRI connectivity: Morphological foundation and plasticity NEUROIMAGE Zhou, I. Y., Liang, Y., Chan, R. W., Gao, P. P., Cheng, J. S., Hu, Y., So, K., Wu, E. X. 2014; 84: 1-10

    Abstract

    Despite the immense ongoing efforts to map brain functional connections and organizations with resting-state functional MRI (rsfMRI), the mechanisms governing the temporally coherent rsfMRI signals remain unclear. In particular, there is a lack of direct evidence regarding the morphological foundation and plasticity of these rsfMRI derived connections. In this study, we investigated the role of axonal projections in rsfMRI connectivity and its plasticity. Well-controlled rodent models of complete and posterior corpus callosotomy were longitudinally examined with rsfMRI at 7T in conjunction with intracortical EEG recording and functional MRI tracing of interhemispheric neuronal pathways by manganese (Mn(2+)). At post-callosotomy day 7, significantly decreased interhemispheric rsfMRI connectivity was observed in both groups in the specific cortical areas whose callosal connections were severed. At day 28, the disrupted connectivity was restored in the partial callosotomy group but not in the complete callosotomy group, likely due to the compensation that occurred through the remaining interhemispheric axonal pathways. This restoration - along with the increased intrahemispheric functional connectivity observed in both groups at day 28 - highlights the remarkable adaptation and plasticity in brain rsfMRI connections. These rsfMRI findings were paralleled by the intracortical EEG recording and Mn(2+) tracing results. Taken together, our experimental results directly demonstrate that axonal connections are the indispensable foundation for rsfMRI connectivity and that such functional connectivity can be plastic and dynamically reorganized atop the morphological connections.

    View details for DOI 10.1016/j.neuroimage.2013.08.037

    View details for Web of Science ID 000328868600001

    View details for PubMedID 23988270

  • Longitudinal metabolic changes in the hippocampus and thalamus of the maternal brain revealed by proton magnetic resonance spectroscopy NEUROSCIENCE LETTERS Zhou, I. Y., Chan, R. W., Ho, L. C., Wu, E. X. 2013; 553: 170-175

    Abstract

    Pregnancy is accompanied by dramatic hormonal changes, which are essential for the display of maternal behaviors. Reproductive hormones have been shown to remodel the neuronal structure and function of the female brain. However, most previous studies have examined the structural and functional changes elicited by transient fluctuations in reproductive hormones. The impact of naturally elevated and more sustained hormonal alterations during pregnancy and lactation are not fully understood. Further alterations in neurochemistry, which may result in substantial changes in the structure and function of neurons that are associated with behavioral modifications in the maternal female, are difficult to capture in a longitudinal and non-invasive manner. In this study, neurobiological alterations during pregnancy and motherhood were investigated longitudinally using non-invasive proton magnetic resonance spectroscopy ((1)H MRS) at 7T in regions related to learning and memory, such as the hippocampus, and in structures involved in alertness and attention, such as the thalamus. Pregnant primiparous rats (N=15) were studied at three days before mating, gestational day 17, lactation day 7 and post-weaning day 7. Age-matched nulliparous female rats (N=9) served as non-pregnant controls. Significantly higher N-acetylaspartate (NAA) levels were observed in the hippocampus and thalamus of rats at gestational day 17. These increases may be associated with increased dendritic sprouting, synaptogenesis or neurogenesis, thereby facilitating supporting behaviors that involve spatial learning and memory and alleviating fear and stress. The (1)H MRS detection of ongoing neurochemical changes induced by pregnancy, especially in the hippocampus, can shed light on the neurochemical underpinnings of behavioral modifications, including the improvement in spatial learning and memory, during pregnancy.

    View details for DOI 10.1016/j.neulet.2013.08.041

    View details for Web of Science ID 000326008700032

    View details for PubMedID 23994391

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