Research Topics
| Srikantan NagarajanSummaryAffiliation: University of California Country: USA Publications
Research Grants
| Collaborators
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Detail Information
Publications
Application of an MEG eigenspace beamformer to reconstructing spatio-temporal activities of neural sourcesKensuke Sekihara
Department of Electronic Systems and Engineering, Tokyo Metropolitan Institute of Technology, Asahigaoka 6 6, Hino, Tokyo 191 0065, Japan
Hum Brain Mapp 15:199-215. 2002..Such a prewhitened eigenspace beamformer was experimentally demonstrated to be useful when large background activity exists...
Spatiotemporal integration of tactile information in human somatosensory cortexZhao Zhu
Biomagnetic Imaging Laboratory, Department of Radiology, University of California, San Francisco, San Francisco, CA, 94143 0628, USA
BMC Neurosci 8:21. 2007....- The relationship between magnetic and electrophysiological responses to complex tactile stimuliZhao Zhu
Biomagnetic Imaging Laboratory, Department of Radiology, University of California San Francisco, San Francisco, CA 94143 0628, USA
BMC Neurosci 10:4. 2009..Stimuli were applied to the fingertips with three inter-stimulus intervals (ISIs): 0.33s, 1s and 2s... - Speech target modulates speaking induced suppression in auditory cortexMaria I Ventura
Department of Otolaryngology, University of California, San Francisco, San Francisco, CA, USA
BMC Neurosci 10:58. 2009.... 
Preoperative localization of hand motor cortex by adaptive spatial filtering of magnetoencephalography dataSrikantan Nagarajan
Biomagnetic Imaging Laboratory, Department of Radiology, University of California, San Francisco, California 94143 0628, USA
J Neurosurg 109:228-37. 2008....- A probabilistic algorithm integrating source localization and noise suppression for MEG and EEG dataJohanna M Zumer
Biomagnetic Imaging Lab, Department of Radiology, University of California, San Francisco, San Francisco, CA 94143 0628, USA
Neuroimage 37:102-15. 2007..Success of this algorithm using MEG data for localizing bilateral auditory cortex, low-SNR somatosensory activations, and for localizing an epileptic spike source are also demonstrated... - Accurate reconstruction of brain activity and functional connectivity from noisy MEG dataJulia P Owen
Biomagnetic Imaging Laboratory, Dept Radiology and Biomedical Imaging, UCSF San Francisco, CA, USA
Conf Proc IEEE Eng Med Biol Soc 2009:65-8. 2009..We demonstrate that brain source activity inferred from this algorithm is better suited to uncover the interactions between brain areas as compared to other commonly used source localization algorithms... - Five-dimensional neuroimaging: localization of the time-frequency dynamics of cortical activitySarang S Dalal
Department of Radiology, University of California, San Francisco, CA 94143 0628, USA
Neuroimage 40:1686-700. 2008..This method enables the ultimate promise of MEG and EEG for five-dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics during cognition... - MEG in the macaque monkey and human: distinguishing cortical fields in space and timeJohanna M Zumer
Department of Radiology, University of California, San Francisco, CA, USA
Brain Res 1345:110-24. 2010..We thus demonstrate the feasibility of using MEG in the macaque monkey and provide a non-human primate model for examining the relationship between external evoked magnetic fields and their underlying neural sources... - Mapping functional connectivity in patients with brain lesionsAdrian G Guggisberg
Biomagnetic Imaging Lab, Department of Radiology, University of California San Francisco, San Francisco, CA 94143 0628, USA
Ann Neurol 63:193-203. 2008..Based on the rationale that damaged brain tissue is disconnected from the physiological interactions among healthy areas, this study aimed to map the functionality of brain areas according to their connectivity with other areas... - Timing is everything: neural response dynamics during syllable processing and its relation to higher-order cognition in schizophrenia and healthy comparison subjectsCorby L Dale
Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA
Int J Psychophysiol 75:183-93. 2010.... - Neural mechanisms of the time-order error: an MEG studyIlana S Hairston
Department of Psychology, University of California, Berkeley, CA 94720, USA
J Cogn Neurosci 19:1163-74. 2007..This was observed only in the two 5-Hz conditions. Combined, these results suggest that the TOE reflects the emergence of an internal representation of the standard, and that the M300 is potentially a neural correlate of plasticity... - Functional organization and hemispheric comparison of primary auditory cortex in the common marmoset (Callithrix jacchus)Bénédicte Philibert
Coleman Memorial Laboratory and W M Keck Center for Integrative Neuroscience, Department of Otolaryngology Head and Neck Surgery, University of California, San Francisco, San Francisco, California 94143 0732, USA
J Comp Neurol 487:391-406. 2005..The overall results indicate that the basic functional organization between hemispheres is similar but not identical... - Comparison of time-frequency responses and the event-related potential to auditory speech stimuli in human cortexErik Edwards
Department of Psychology and Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA, USA
J Neurophysiol 102:377-86. 2009..Across electrodes, the alpha suppression from 200 to 450 ms correlated with the preceding (50-200 ms) gammahigh increase. The results are discussed in terms of the different physiological origins of these electrocortical signals... - Robust Bayesian estimation of the location, orientation, and time course of multiple correlated neural sources using MEGDavid P Wipf
Department of Radiology and Biomedical Imaging, University of California San Francisco, 513 Parnassus Avenue, San Francisco, CA 94143, USA
Neuroimage 49:641-55. 2010..Empirical results on both simulated and real data sets verify the efficacy of this approach... - A graphical model for estimating stimulus-evoked brain responses from magnetoencephalography data with large background brain activitySrikantan S Nagarajan
Biomagnetic Imaging Laboratory, Department of Radiology, University of California at San Francisco, San Francisco, CA 94122, USA
Neuroimage 30:400-16. 2006..We demonstrate on real and simulated data that the algorithm outperforms benchmark methods for denoising and separation. We also show that the algorithm improves the performance of localization with beamforming algorithms... - Magnetoencephalographic evidence for a precise forward model in speech productionTheda H Heinks-Maldonado
Department of Otolaryngology, University of California, San Francisco, California 94143, USA
Neuroreport 17:1375-9. 2006..This suggests that the feedback comparison process may be very precise, allowing the auditory system to distinguish between internal and external sources of auditory information... - Localization of neurosurgically implanted electrodes via photograph-MRI-radiograph coregistrationSarang S Dalal
Biomagnetic Imaging Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA 94143 0628, USA
J Neurosci Methods 174:106-15. 2008..We demonstrate the results of our method in eight epilepsy patients implanted with electrode grids spanning the left hemisphere... - Neuroimaging characteristics of patients with focal hand dystoniaLeighton B N Hinkley
Department of Radiology, University of California, San Francisco, San Francisco, California 94143 0628, USA
J Hand Ther 22:125-34; quiz 135. 2009..Continued collaborations between health professionals who treat FHd and research scientists who examine the brain using neuroimaging tools are imperative for answering difficult questions about patients with specific movement disorders... - Accuracy of diffusion tensor magnetic resonance imaging tractography assessed using intraoperative subcortical stimulation mapping and magnetic source imagingJeffrey I Berman
Department of Radiology, University of California, San Francisco 94107, USA
J Neurosurg 107:488-94. 2007..The goal of this study was to use intraoperative subcortical stimulation mapping of the motor tract and magnetic source imaging to validate the utility of DT-imaged fiber tracking as a tool for presurgical planning... - Modulation of the auditory cortex during speech: an MEG studyJohn F Houde
Center for Integrative Neuroscience, University of California, San Francisco 94143, USA
J Cogn Neurosci 14:1125-38. 2002..These data suggest that during speech production, the auditory cortex (1) attenuates its sensitivity and (2) modulates its activity as a function of the expected acoustic feedback... - Correlation of clinical neuromusculoskeletal and central somatosensory performance: variability in controls and patients with severe and mild focal hand dystoniaNancy N Byl
Dept of Physical Therapy and Rehabilitation Science, School of Medicine, University of California, San Francisco, California 94143 0736, USA
Neural Plast 9:177-203. 2002..Training must be individualized to each patient to rebalance the sensorimotor feedback loop and to restore normal fine motor control... - Modified beamformers for coherent source region suppressionSarang S Dalal
UCSF Berkeley Joint Graduate Group in Bioengineering, Department of Radiology, University of California, San Francisco, CA 94143 0628, USA
IEEE Trans Biomed Eng 53:1357-63. 2006..After defining a suppression region containing the temporal cortex on one side, the described method consistently results in clear focal activations at expected regions of the contralateral superior temporal plane... - Subcortical pathways serving cortical language sites: initial experience with diffusion tensor imaging fiber tracking combined with intraoperative language mappingRoland G Henry
Department of Radiology, University of California, San Francisco, San Francisco, CA 94143, USA
Neuroimage 21:616-22. 2004..The combined techniques may provide improved preservation of eloquent regions during neurological surgery, and may provide access to direct connectivity information between functional regions of the brain... - A probabilistic algorithm for robust interference suppression in bioelectromagnetic sensor dataSrikantan S Nagarajan
Department of Radiology, University of California at San Francisco, 513 Parnassus Avenue 5362, San Francisco, CA 94122, USA
Stat Med 26:3886-910. 2007..This algorithm is found to be robust and efficient and significantly superior to many other existing approaches on real and simulated data... - Controlled Support MEG imagingSrikantan S Nagarajan
Biomagnetic Imaging Laboratory, Department of Radiology, University of California at San Francisco, San Francisco, CA 94122, USA
Neuroimage 33:878-85. 2006..The paper discusses the underlying Tikhonov theory and its relationship to a Bayesian formulation which in turn allows us to interpret and better understand other related algorithms... - Magnetic source imaging for the surgical evaluation of electroencephalography-confirmed secondary bilateral synchrony in intractable epilepsyEdward F Chang
Department of Neurological Surgery, University of California, San Francisco, 505 Parnassus Avenue, Room M779, San Francisco, California 94143, USA
J Neurosurg 111:1248-56. 2009..Whole-head magnetoencephalography (MEG) has superior spatial resolution compared with traditional EEG, and can potentially elucidate seizure foci in challenging epilepsy cases in which patients are undergoing evaluation for surgery... - Plasticity in primary auditory cortex of monkeys with altered vocal productionSteven W Cheung
Coleman Memorial Laboratory and W M Keck Center for Integrative Neuroscience, Department of Otolaryngology Head and Neck Surgery, University of California, San Francisco, California 94143 0342, USA
J Neurosci 25:2490-503. 2005..These findings suggest a previously unrecognized form of cortical plasticity that is specific to higher-order processes involved in the discrimination of more complex sounds, such as species-specific vocalizations... - Concordance between routine interictal magnetoencephalography and simultaneous scalp electroencephalography in a sample of patients with epilepsyHeidi E Kirsch
UCSF Epilepsy Center, Department of Neurology, University of California, San Francisco, CA 94143 0138, USA
J Clin Neurophysiol 24:215-31. 2007..In some cases, EEG and MEG are synergistic and provide complementary information... - Probabilistic algorithms for MEG/EEG source reconstruction using temporal basis functions learned from dataJohanna M Zumer
Biomagnetic Imaging Lab, Department of Radiology, University of California, San Francisco, San Francisco, CA 94143 0628, USA
Neuroimage 41:924-40. 2008..Performance in simulations and real data, both with large noise and interference and/or correlated sources, demonstrates significant improvement over existing source localization methods... - Spatiotemporal imaging of cortical activation during verb generation and picture namingErik Edwards
Department of Psychology and Helen Wills Neuroscience Institute, University of California, Berkeley, CA, USA
Neuroimage 50:291-301. 2010..The data are discussed with regards to current leading models of speech perception and production, and a "dual ventral stream" hybrid of leading speech perception models is given... - A unified Bayesian framework for MEG/EEG source imagingDavid Wipf
Biomagnetic Imaging Lab, University of California San Francisco, San Francisco, CA 94143, USA
Neuroimage 44:947-66. 2009.... - Fast oscillations associated with interictal spikes localize the epileptogenic zone in patients with partial epilepsyAdrian G Guggisberg
Biomagnetic Imaging Laboratory, Department of Radiology, University of California San Francisco, San Francisco, CA 94143 0628, USA
Neuroimage 39:661-8. 2008..Imaging of spike-locked beta/gamma power changes therefore seems to be a reliable and fast alternative to conventional MEG techniques for localizing epileptogenic tissue, in particular, if more than 50 interictal spikes can be recorded... - Computerized cognitive training restores neural activity within the reality monitoring network in schizophreniaKaruna Subramaniam
San Francisco Department of Veterans Affairs Medical Center and Department of Psychiatry, University of California, San Francisco, San Francisco, CA 94121, USA
Neuron 73:842-53. 2012..These findings demonstrate that a serious behavioral deficit in schizophrenia, and its underlying neural dysfunction, can be improved by well-designed computerized cognitive training, resulting in better quality of life... - Sensory representation abnormalities that parallel focal hand dystonia in a primate modelDavid T Blake
Coleman Laboratory, Keck Center for Integrative Neuroscience, and Department of Otolaryngology Head and Neck Surgery, University of California, San Francisco, USA
Somatosens Mot Res 19:347-57. 2002..Thalamic mapping demonstrated proportionate levels of abnormality in thalamic representations as were found in cortical representations... - Performance comparison of six independent components analysis algorithms for fetal signal extraction from real fMCG dataKenneth E Hild
Department of Radiology, University of California at San Francisco, San Francisco, CA 94122, USA
Phys Med Biol 52:449-62. 2007..It is possible to explain these differences by assuming that the number of point sources needed to completely explain the data is larger than the dimensionality used in the ICA extraction... - Source localization of EEG/MEG data by correlating columns of ICA and lead field matricesKenneth E Hild
Department of Radiology, University of California at San Francisco, San Francisco, CA 94143, USA
IEEE Trans Biomed Eng 56:2619-26. 2009..We show that, when synthetic data are used, the proposed localization method produces a smaller localization error than several alternatives. We also show localization results for real auditory-evoked MEG data... - An expectation-maximization method for spatio-temporal blind source separation using an AR-MOG source modelKenneth E Hild
Department of Radiology, The University of California at San Francisco, San Francisco, CA 94143, USA
IEEE Trans Neural Netw 19:508-19. 2008..We also show results for using AR-MOG to extract the fetal cardiac signal from real magnetocardiographic (MCG) data... - Performance of an MEG adaptive-beamformer technique in the presence of correlated neural activities: effects on signal intensity and time-course estimatesKensuke Sekihara
Department of Electronic Systems and Engineering, Tokyo Metropolitan Institute of Technology, Tokyo 191 0065, Japan
IEEE Trans Biomed Eng 49:1534-46. 2002..Our numerical experiments demonstrated that reasonably accurate time courses can be retrieved from considerably distorted time courses even when the signal-to-noise ratio is low... - Representation of spectral and temporal envelope of twitter vocalizations in common marmoset primary auditory cortexSrikantan S Nagarajan
Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112 9458, USA
J Neurophysiol 87:1723-37. 2002..Neurophysiological data reflecting response sensitivity in AI to these forms of degradation closely parallel human psychophysical results on the intelligibility of degraded speech in quiet and noisy conditions... - Performance of an MEG adaptive-beamformer source reconstruction technique in the presence of additive low-rank interferenceKensuke Sekihara
Department of Electronic Systems and Engineering, Tokyo Metropolitan Institute of Technology, Asahigaoka 6 6, Hino, Tokyo 191 0065, Japan
IEEE Trans Biomed Eng 51:90-9. 2004..Four types of numerical examples verifying this conclusion are presented... - Analysis of efficiency of magnetic stimulationKai-Hsiung Hsu
Neural Engineering Center, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA
IEEE Trans Biomed Eng 50:1276-85. 2003..Moreover, the cloverleaf design achieves the highest efficiency for infinitely long fibers whereas the butterfly design is optimal for terminating or bending fibers... - Asymptotic SNR of scalar and vector minimum-variance beamformers for neuromagnetic source reconstructionKensuke Sekihara
Department of Electronic Systems and Engineering, Tokyo Metropolitan Institute of Technology, Tokyo 191 0065, Japan
IEEE Trans Biomed Eng 51:1726-34. 2004..The comparison shows that the beamformer with optimum direction gives an output SNR superior to that of the conventional vector beamformer. Numerical examples validating the results of the analysis are presented... - Localization bias and spatial resolution of adaptive and non-adaptive spatial filters for MEG source reconstructionKensuke Sekihara
Department of Electronic Systems and Engineering, Tokyo Metropolitan Institute of Technology, Asahigaoka 6 6, Hino, Tokyo 191 0065, Japan
Neuroimage 25:1056-67. 2005..The results of these analyses are validated by numerical experiments as well as by reconstructions based on two sets of evoked magnetic responses... - A simple nonparametric statistical thresholding for MEG spatial-filter source reconstruction imagesKensuke Sekihara
Department of Systems Design and Engineering, Tokyo Metropolitan University, Asahigaoka 6 6, Hino, Tokyo 191 0065, Japan
Neuroimage 27:368-76. 2005..The results of applying the proposed method to auditory-evoked measurements are presented to demonstrate the method's effectiveness... - A novel adaptive beamformer for MEG source reconstruction effective when large background brain activities existKensuke Sekihara
Department of Systems Design and Engineering, Tokyo Metropolitan University, Japan
IEEE Trans Biomed Eng 53:1755-64. 2006..A numerical example, as well as applications to two types of MEG data, demonstrates the effectiveness of the proposed method... - Sensorimotor integration in S2, PV, and parietal rostroventral areas of the human sylvian fissureLeighton B Hinkley
Center for Neuroscience, University of California Davis, 1544 Newton Court, Davis, CA 95618, USA
J Neurophysiol 97:1288-97. 2007.... - Auditory cortical plasticity in learning to discriminate modulation rateVirginie van Wassenhove
Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
J Neurosci 27:2663-72. 2007..Functional plasticity in auditory cortex is here interpreted as the product of bottom-up and top-down modulations... - Predicting the location of mouth motor cortex in patients with brain tumors by using somatosensory evoked field measurementsHeidi E Kirsch
University of California San Francisco Epilepsy Center, Department of Neurology, USA
J Neurosurg 107:481-7. 2007..Preoperative localization of face somatosensory cortex with magnetoencephalography (MEG) may allow the surgeon to predict the location of mouth motor areas... - Spatial localization of cortical time-frequency dynamicsSarang S Dalal
Mental Processes and Brain Activation Lab, INSERM U821, 69675 Bron, France
Conf Proc IEEE Eng Med Biol Soc 2007:4941-4. 2007..This method enables non-invasive five-dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics... - Motor field sensitivity for preoperative localization of motor cortexPeter T Lin
Department of Neurology, Stanford Hospital and Clinics, Stanford, California, USA
J Neurosurg 105:588-94. 2006..CONCLUSIONS: The findings in this study suggest that single-dipole localization for the analysis of motor data is not sufficiently sensitive and is nonspecific, and thus not clinically useful...
Research Grants
- Cortical spatiotemporal plasticity in humansSrikantan Nagarajan; Fiscal Year: 2009..By comparing characteristics of behavioral improvements with cortical plasticity we propose to unravel general rules of cortical spatiotemporal plasticity associated with auditory perceptual learning. ..
- Neural mechanisms of auditory feedback during speechSrikantan Nagarajan; Fiscal Year: 2007....
- Cortical spatiotemporal plasticity in humansSrikantan Nagarajan; Fiscal Year: 2004..These results in normal individuals should provide crucial information for the development, refinement and evaluation of diagnosis and therapy for individuals with learning disability. ..
- Cortical spatiotemporal plasticity in humansSrikantan S Nagarajan; Fiscal Year: 2010..By comparing characteristics of behavioral improvements with cortical plasticity we propose to unravel general rules of cortical spatiotemporal plasticity associated with auditory perceptual learning. ..