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Volumn 8, Issue 9, 2013, Pages

Long-Term Effects of Attentional Performance on Functional Brain Network Topology

Author keywords

[No Author keywords available]

Indexed keywords

ADULT; ANTERIOR CINGULATE; ARTICLE; ATTENTION; BRAIN FUNCTION; BRAIN REGION; COGNITION; COPING BEHAVIOR; FEMALE; FOREBRAIN; FUNCTIONAL ASSESSMENT; FUNCTIONAL MAGNETIC RESONANCE IMAGING; HEAD MOVEMENT; HUMAN; HUMAN EXPERIMENT; LINGUAL GYRUS; MALE; NORMAL HUMAN; PARIETAL CORTEX; PRIMARY SOMATOSENSORY CORTEX; RESTING STATE NETWORK; SUPERIOR FRONTAL GYRUS; SUPERIOR TEMPORAL GYRUS; TASK PERFORMANCE; VISUAL CORTEX; AROUSAL; BRAIN; BRAIN MAPPING; NUCLEAR MAGNETIC RESONANCE IMAGING; PHYSIOLOGY; PSYCHOMOTOR PERFORMANCE; YOUNG ADULT;

EID: 84883627191     PISSN: None     EISSN: 19326203     Source Type: Journal    
DOI: 10.1371/journal.pone.0074125     Document Type: Article
Times cited : (46)

References (69)
  • 1
    • 49349116300 scopus 로고    scopus 로고
    • Signal salience and the mindlessness theory of vigilance
    • Helton WS, Warm JS, (2008) Signal salience and the mindlessness theory of vigilance. Acta Psychol (Amst) 129: 18-25.
    • (2008) Acta Psychol (Amst) , vol.129 , pp. 18-25
    • Helton, W.S.1    Warm, J.S.2
  • 2
    • 0002806541 scopus 로고    scopus 로고
    • The attentive brain
    • In: Parasuraman R, editor. Cambridge: MIT Press
    • Parasuraman R, Warm JS, See JE (1998) The attentive brain. In: Parasuraman R, editor. Brain systems of vigilance. Cambridge: MIT Press. 221-256.
    • (1998) Brain systems of vigilance , pp. 221-256
    • Parasuraman, R.1    Warm, J.S.2    See, J.E.3
  • 3
    • 47749146479 scopus 로고    scopus 로고
    • Vigilance requires hard mental work and is stressful
    • Warm JS, Parasuraman R, Matthews G, (2008) Vigilance requires hard mental work and is stressful. Hum Factors 50: 433-441.
    • (2008) Hum Factors , vol.50 , pp. 433-441
    • Warm, J.S.1    Parasuraman, R.2    Matthews, G.3
  • 4
    • 60549103853 scopus 로고    scopus 로고
    • Complex brain networks: graph theoretical analysis of structural and functional systems
    • Bullmore E, Sporns O (2009) Complex brain networks: graph theoretical analysis of structural and functional systems (vol 10, pg 186, 2009). Nature Reviews Neuroscience 10.
    • (2009) Nature Reviews Neuroscience , vol.10 , pp. 186
    • Bullmore, E.1    Sporns, O.2
  • 8
    • 0035148422 scopus 로고    scopus 로고
    • Overall vigilance and sustained attention decrements in healthy aging
    • Berardi A, Parasuraman R, Haxby JV, (2001) Overall vigilance and sustained attention decrements in healthy aging. Experimental aging research 27: 19-39.
    • (2001) Experimental Aging Research , vol.27 , pp. 19-39
    • Berardi, A.1    Parasuraman, R.2    Haxby, J.V.3
  • 9
    • 27744549029 scopus 로고    scopus 로고
    • Top-down suppression deficit underlies working memory impairment in normal aging
    • Gazzaley A, Cooney JW, Rissman J, D'Esposito M, (2005) Top-down suppression deficit underlies working memory impairment in normal aging. Nature Neuroscience 8: 1298-1300.
    • (2005) Nature Neuroscience , vol.8 , pp. 1298-1300
    • Gazzaley, A.1    Cooney, J.W.2    Rissman, J.3    D'Esposito, M.4
  • 11
    • 77249090194 scopus 로고    scopus 로고
    • Age-related changes in topological patterns of large-scale brain functional networks during memory encoding and recognition
    • Wang L, Li Y, Metzak P, He Y, Woodward TS, (2010) Age-related changes in topological patterns of large-scale brain functional networks during memory encoding and recognition. Neuroimage 50: 862-872.
    • (2010) Neuroimage , vol.50 , pp. 862-872
    • Wang, L.1    Li, Y.2    Metzak, P.3    He, Y.4    Woodward, T.S.5
  • 12
    • 59949084588 scopus 로고    scopus 로고
    • Altered small-world brain functional networks in children with attention-deficit/hyperactivity disorder
    • Wang L, Zhu C, He Y, Zang Y, Cao Q, et al. (2009) Altered small-world brain functional networks in children with attention-deficit/hyperactivity disorder. Human brain mapping 30: 638-649.
    • (2009) Human Brain Mapping , vol.30 , pp. 638-649
    • Wang, L.1    Zhu, C.2    He, Y.3    Zang, Y.4    Cao, Q.5
  • 13
    • 78249275549 scopus 로고    scopus 로고
    • Loss of 'small-world' networks in Alzheimer's disease: graph analysis of FMRI resting-state functional connectivity
    • Sanz-Arigita EJ, Schoonheim MM, Damoiseaux JS, Rombouts SA, Maris E, et al. (2010) Loss of 'small-world' networks in Alzheimer's disease: graph analysis of FMRI resting-state functional connectivity. PLoS One 5: e13788.
    • (2010) PLoS One , vol.5
    • Sanz-Arigita, E.J.1    Schoonheim, M.M.2    Damoiseaux, J.S.3    Rombouts, S.A.4    Maris, E.5
  • 15
    • 44949216609 scopus 로고    scopus 로고
    • The power of spectral density analysis for mapping endogenous BOLD signal fluctuations
    • Duff EP, Johnston LA, Xiong J, Fox PT, Mareels I, et al. (2008) The power of spectral density analysis for mapping endogenous BOLD signal fluctuations. Hum Brain Mapp 29: 778-790.
    • (2008) Hum Brain Mapp , vol.29 , pp. 778-790
    • Duff, E.P.1    Johnston, L.A.2    Xiong, J.3    Fox, P.T.4    Mareels, I.5
  • 16
    • 11244349935 scopus 로고    scopus 로고
    • Effect of prior cognitive state on resting state networks measured with functional connectivity
    • Waites AB, Stanislavsky A, Abbott DF, Jackson GD, (2005) Effect of prior cognitive state on resting state networks measured with functional connectivity. Hum Brain Mapp 24: 59-68.
    • (2005) Hum Brain Mapp , vol.24 , pp. 59-68
    • Waites, A.B.1    Stanislavsky, A.2    Abbott, D.F.3    Jackson, G.D.4
  • 17
    • 67149094277 scopus 로고    scopus 로고
    • The resting human brain and motor learning
    • Albert NB, Robertson EM, Miall RC, (2009) The resting human brain and motor learning. Curr Biol 19: 1023-1027.
    • (2009) Curr Biol , vol.19 , pp. 1023-1027
    • Albert, N.B.1    Robertson, E.M.2    Miall, R.C.3
  • 19
    • 77955938953 scopus 로고    scopus 로고
    • Correlated low-frequency BOLD fluctuations in the resting human brain are modulated by recent experience in category-preferential visual regions
    • Stevens WD, Buckner RL, Schacter DL, (2010) Correlated low-frequency BOLD fluctuations in the resting human brain are modulated by recent experience in category-preferential visual regions. Cereb Cortex 20: 1997-2006.
    • (2010) Cereb Cortex , vol.20 , pp. 1997-2006
    • Stevens, W.D.1    Buckner, R.L.2    Schacter, D.L.3
  • 20
    • 69949156127 scopus 로고    scopus 로고
    • Endogenous Human Brain Dynamics Recover Slowly Following Cognitive Effort
    • Barnes A, Bullmore ET, Suckling J (2009) Endogenous Human Brain Dynamics Recover Slowly Following Cognitive Effort. Plos One 4.
    • (2009) Plos One , vol.4
    • Barnes, A.1    Bullmore, E.T.2    Suckling, J.3
  • 21
    • 84876072488 scopus 로고    scopus 로고
    • Human brain functional network changes associated with enhanced and impaired attentional task performance
    • Giessing C, Thiel CM, Alexander-Bloch AF, Patel AX, Bullmore ET, (2013) Human brain functional network changes associated with enhanced and impaired attentional task performance. J Neurosci 33: 5903-5914.
    • (2013) J Neurosci , vol.33 , pp. 5903-5914
    • Giessing, C.1    Thiel, C.M.2    Alexander-Bloch, A.F.3    Patel, A.X.4    Bullmore, E.T.5
  • 22
    • 34548014282 scopus 로고    scopus 로고
    • Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging
    • Fox MD, Raichle ME, (2007) Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging. Nat Rev Neurosci 8: 700-711.
    • (2007) Nat Rev Neurosci , vol.8 , pp. 700-711
    • Fox, M.D.1    Raichle, M.E.2
  • 24
    • 69249124954 scopus 로고    scopus 로고
    • Functional Connectivity Between the Thalamus and Visual Cortex Under Eyes Closed and Eyes Open Conditions: A Resting-State fMRI Study
    • Zou QH, Long XY, Zuo XN, Yan CG, Zhu CZ, et al. (2009) Functional Connectivity Between the Thalamus and Visual Cortex Under Eyes Closed and Eyes Open Conditions: A Resting-State fMRI Study. Human Brain Mapping 30: 3066-3078.
    • (2009) Human Brain Mapping , vol.30 , pp. 3066-3078
    • Zou, Q.H.1    Long, X.Y.2    Zuo, X.N.3    Yan, C.G.4    Zhu, C.Z.5
  • 25
    • 79952703800 scopus 로고    scopus 로고
    • Impact of brain networks involved in vigilance on processing irrelevant visual motion
    • Breckel TP, Giessing C, Thiel CM, (2011) Impact of brain networks involved in vigilance on processing irrelevant visual motion. NeuroImage 55: 1754-1762.
    • (2011) NeuroImage , vol.55 , pp. 1754-1762
    • Breckel, T.P.1    Giessing, C.2    Thiel, C.M.3
  • 27
    • 21944448369 scopus 로고    scopus 로고
    • Generalisability, Random Effects & Population Inference
    • Holmes AP, Friston KJ (1998) Generalisability, Random Effects & Population Inference. Neuroimage 7.
    • (1998) Neuroimage , vol.7
    • Holmes, A.P.1    Friston, K.J.2
  • 28
    • 0000435568 scopus 로고
    • Development and Use of Stanford Sleepiness Scale (Sss)
    • Hoddes E, Zarcone V, Dement W (1972) Development and Use of Stanford Sleepiness Scale (Sss). Psychophysiology 9: 150.
    • (1972) Psychophysiology , vol.9 , pp. 150
    • Hoddes, E.1    Zarcone, V.2    Dement, W.3
  • 29
    • 78149420706 scopus 로고    scopus 로고
    • Network scaling effects in graph analytic studies of human resting-state FMRI data
    • Fornito A, Zalesky A, Bullmore ET, (2010) Network scaling effects in graph analytic studies of human resting-state FMRI data. Frontiers in Systems Neuroscience 4: 22.
    • (2010) Frontiers in Systems Neuroscience , vol.4 , pp. 22
    • Fornito, A.1    Zalesky, A.2    Bullmore, E.T.3
  • 31
    • 36148947506 scopus 로고    scopus 로고
    • A simple view of the brain through a frequency-specific functional connectivity measure
    • Salvador R, Martinez A, Pomarol-Clotet E, Gomar J, Vila F, et al. (2008) A simple view of the brain through a frequency-specific functional connectivity measure. Neuroimage 39: 279-289.
    • (2008) Neuroimage , vol.39 , pp. 279-289
    • Salvador, R.1    Martinez, A.2    Pomarol-Clotet, E.3    Gomar, J.4    Vila, F.5
  • 32
    • 77349095673 scopus 로고    scopus 로고
    • Whole-brain anatomical networks: does the choice of nodes matter?
    • Zalesky A, Fornito A, Harding IH, Cocchi L, Yucel M, et al. (2010) Whole-brain anatomical networks: does the choice of nodes matter? Neuroimage 50: 970-983.
    • (2010) Neuroimage , vol.50 , pp. 970-983
    • Zalesky, A.1    Fornito, A.2    Harding, I.H.3    Cocchi, L.4    Yucel, M.5
  • 35
    • 67049122306 scopus 로고    scopus 로고
    • Functionally Linked Resting-State Networks Reflect the Underlying Structural Connectivity Architecture of the Human Brain
    • van den Heuvel MP, Mandl RCW, Kahn RS, Pol HEH, (2009) Functionally Linked Resting-State Networks Reflect the Underlying Structural Connectivity Architecture of the Human Brain. Human Brain Mapping 30: 3127-3141.
    • (2009) Human Brain Mapping , vol.30 , pp. 3127-3141
    • van den Heuvel, M.P.1    Mandl, R.C.W.2    Kahn, R.S.3    Pol, H.E.H.4
  • 40
    • 79960882474 scopus 로고    scopus 로고
    • Brain network analysis: separating cost from topology using cost-integration
    • Ginestet CE, Nichols TE, Bullmore ET, Simmons A, (2011) Brain network analysis: separating cost from topology using cost-integration. PLoS One 6: e21570.
    • (2011) PLoS One , vol.6
    • Ginestet, C.E.1    Nichols, T.E.2    Bullmore, E.T.3    Simmons, A.4
  • 41
    • 35348957264 scopus 로고    scopus 로고
    • Efficient behavior of small-world networks
    • Latora V, Marchiori M, (2001) Efficient behavior of small-world networks. Phys Rev Lett 87: 198701.
    • (2001) Phys Rev Lett , vol.87 , pp. 198701
    • Latora, V.1    Marchiori, M.2
  • 42
    • 18244392161 scopus 로고    scopus 로고
    • Economic small-world behavior in weighted networks
    • Latora V, Marchiori M, (2003) Economic small-world behavior in weighted networks. European Physical Journal B 32: 249-263.
    • (2003) European Physical Journal B , vol.32 , pp. 249-263
    • Latora, V.1    Marchiori, M.2
  • 43
    • 0032482432 scopus 로고    scopus 로고
    • Collective dynamics of 'small-world' networks
    • Watts DJ, Strogatz SH, (1998) Collective dynamics of 'small-world' networks. Nature 393: 440-442.
    • (1998) Nature , vol.393 , pp. 440-442
    • Watts, D.J.1    Strogatz, S.H.2
  • 45
    • 78650609984 scopus 로고    scopus 로고
    • Spurious but systematic correlations in functional connectivity MRI networks arise from subject motion
    • Power JD, Barnes KA, Snyder AZ, Schlaggar BL, Petersen SE (2011) Spurious but systematic correlations in functional connectivity MRI networks arise from subject motion. Neuroimage.
    • (2011) Neuroimage
    • Power, J.D.1    Barnes, K.A.2    Snyder, A.Z.3    Schlaggar, B.L.4    Petersen, S.E.5
  • 46
    • 74549191147 scopus 로고    scopus 로고
    • Enhanced brain correlations during rest are related to memory for recent experiences
    • Tambini A, Ketz N, Davachi L, (2010) Enhanced brain correlations during rest are related to memory for recent experiences. Neuron 65: 280-290.
    • (2010) Neuron , vol.65 , pp. 280-290
    • Tambini, A.1    Ketz, N.2    Davachi, L.3
  • 47
    • 84856955444 scopus 로고    scopus 로고
    • Age-related changes in the topological architecture of the brain during hand grip
    • Park CH, Boudrias MH, Rossiter H, Ward NS (2012) Age-related changes in the topological architecture of the brain during hand grip. Neurobiol Aging 33: 833 e827-837.
    • (2012) Neurobiol Aging , vol.33 , pp. 827-837
    • Park, C.H.1    Boudrias, M.H.2    Rossiter, H.3    Ward, N.S.4
  • 48
    • 33845940366 scopus 로고    scopus 로고
    • Small-world network organization of functional connectivity of EEG slow-wave activity during sleep
    • Ferri R, Rundo F, Bruni O, Terzano MG, Stam CJ, (2007) Small-world network organization of functional connectivity of EEG slow-wave activity during sleep. Clin Neurophysiol 118: 449-456.
    • (2007) Clin Neurophysiol , vol.118 , pp. 449-456
    • Ferri, R.1    Rundo, F.2    Bruni, O.3    Terzano, M.G.4    Stam, C.J.5
  • 50
    • 40649090533 scopus 로고    scopus 로고
    • Low frequency BOLD fluctuations during resting wakefulness and light sleep: a simultaneous EEG-fMRI study
    • Horovitz SG, Fukunaga M, de Zwart JA, van Gelderen P, Fulton SC, et al. (2008) Low frequency BOLD fluctuations during resting wakefulness and light sleep: a simultaneous EEG-fMRI study. Human Brain Mapping 29: 671-682.
    • (2008) Human Brain Mapping , vol.29 , pp. 671-682
    • Horovitz, S.G.1    Fukunaga, M.2    de Zwart, J.A.3    van Gelderen, P.4    Fulton, S.C.5
  • 52
    • 0036517313 scopus 로고    scopus 로고
    • Control of goal-directed and stimulus-driven attention in the brain
    • Corbetta M, Shulman GL, (2002) Control of goal-directed and stimulus-driven attention in the brain. Nature reviews Neuroscience 3: 201-215.
    • (2002) Nature Reviews Neuroscience , vol.3 , pp. 201-215
    • Corbetta, M.1    Shulman, G.L.2
  • 53
    • 33745163197 scopus 로고    scopus 로고
    • More attention must be paid: the neurobiology of attentional effort
    • Sarter M, Gehring WJ, Kozak R, (2006) More attention must be paid: the neurobiology of attentional effort. Brain Res Rev 51: 145-160.
    • (2006) Brain Res Rev , vol.51 , pp. 145-160
    • Sarter, M.1    Gehring, W.J.2    Kozak, R.3
  • 54
    • 28544442348 scopus 로고    scopus 로고
    • Augmented prefrontal acetylcholine release during challenged attentional performance
    • Kozak R, Bruno JP, Sarter M, (2006) Augmented prefrontal acetylcholine release during challenged attentional performance. Cerebral cortex 16: 9-17.
    • (2006) Cerebral Cortex , vol.16 , pp. 9-17
    • Kozak, R.1    Bruno, J.P.2    Sarter, M.3
  • 55
    • 0030955682 scopus 로고    scopus 로고
    • Time-related changes in neural systems underlying attention and arousal during the performance of an auditory vigilance task
    • Paus T, Zatorre RJ, Hofle N, Caramanos Z, Gotman J, et al. (1997) Time-related changes in neural systems underlying attention and arousal during the performance of an auditory vigilance task. Journal of Cognitive Neuroscience 9: 392-408.
    • (1997) Journal of Cognitive Neuroscience , vol.9 , pp. 392-408
    • Paus, T.1    Zatorre, R.J.2    Hofle, N.3    Caramanos, Z.4    Gotman, J.5
  • 56
    • 0032211048 scopus 로고    scopus 로고
    • A specific role for the thalamus in mediating the interaction of attention and arousal in humans
    • Portas CM, Rees G, Howseman AM, Josephs O, Turner R, et al. (1998) A specific role for the thalamus in mediating the interaction of attention and arousal in humans. Journal of Neuroscience 18: 8979-8989.
    • (1998) Journal of Neuroscience , vol.18 , pp. 8979-8989
    • Portas, C.M.1    Rees, G.2    Howseman, A.M.3    Josephs, O.4    Turner, R.5
  • 57
    • 33747603224 scopus 로고    scopus 로고
    • Vigilance, alertness, or sustained attention: physiological basis and measurement
    • Oken BS, Salinsky MC, Elsas SM, (2006) Vigilance, alertness, or sustained attention: physiological basis and measurement. Clin Neurophysiol 117: 1885-1901.
    • (2006) Clin Neurophysiol , vol.117 , pp. 1885-1901
    • Oken, B.S.1    Salinsky, M.C.2    Elsas, S.M.3
  • 58
    • 0015643352 scopus 로고
    • Toward a Cognitive Social Learning Reconceptualization of Personality
    • Mischel W, (1973) Toward a Cognitive Social Learning Reconceptualization of Personality. Psychological Review 80: 252-283.
    • (1973) Psychological Review , vol.80 , pp. 252-283
    • Mischel, W.1
  • 59
    • 0033800404 scopus 로고    scopus 로고
    • The role of acetylcholine in cortical synaptic plasticity
    • Rasmusson DD, (2000) The role of acetylcholine in cortical synaptic plasticity. Behavioural brain research 115: 205-218.
    • (2000) Behavioural Brain Research , vol.115 , pp. 205-218
    • Rasmusson, D.D.1
  • 60
    • 0028429143 scopus 로고
    • Regional cerebral oxidative and total glucose consumption during rest and activation studied with positron emission tomography
    • Blomqvist G, Seitz RJ, Sjogren I, Halldin C, Stone-Elander S, et al. (1994) Regional cerebral oxidative and total glucose consumption during rest and activation studied with positron emission tomography. Acta physiologica Scandinavica 151: 29-43.
    • (1994) Acta Physiologica Scandinavica , vol.151 , pp. 29-43
    • Blomqvist, G.1    Seitz, R.J.2    Sjogren, I.3    Halldin, C.4    Stone-Elander, S.5
  • 61
    • 0023780085 scopus 로고
    • Nonoxidative glucose consumption during focal physiologic neural activity
    • Fox PT, Raichle ME, Mintun MA, Dence C, (1988) Nonoxidative glucose consumption during focal physiologic neural activity. Science 241: 462-464.
    • (1988) Science , vol.241 , pp. 462-464
    • Fox, P.T.1    Raichle, M.E.2    Mintun, M.A.3    Dence, C.4
  • 63
    • 0026629933 scopus 로고
    • Physical and mental fatigue: metabolic mechanisms and importance of plasma amino acids
    • Newsholme EA, Blomstrand E, Ekblom B, (1992) Physical and mental fatigue: metabolic mechanisms and importance of plasma amino acids. British medical bulletin 48: 477-495.
    • (1992) British Medical Bulletin , vol.48 , pp. 477-495
    • Newsholme, E.A.1    Blomstrand, E.2    Ekblom, B.3
  • 64
    • 47049109643 scopus 로고    scopus 로고
    • Energy limitation as a selective pressure on the evolution of sensory systems
    • Niven JE, Laughlin SB, (2008) Energy limitation as a selective pressure on the evolution of sensory systems. The Journal of experimental biology 211: 1792-1804.
    • (2008) The Journal of Experimental Biology , vol.211 , pp. 1792-1804
    • Niven, J.E.1    Laughlin, S.B.2
  • 65
    • 74049156284 scopus 로고    scopus 로고
    • Intrinsic Functional Connectivity As a Tool For Human Connectomics: Theory, Properties, and Optimization
    • Van Dijk KRA, Hedden T, Venkataraman A, Evans KC, Lazar SW, et al. (2010) Intrinsic Functional Connectivity As a Tool For Human Connectomics: Theory, Properties, and Optimization. Journal of Neurophysiology 103: 297-321.
    • (2010) Journal of Neurophysiology , vol.103 , pp. 297-321
    • Van Dijk, K.R.A.1    Hedden, T.2    Venkataraman, A.3    Evans, K.C.4    Lazar, S.W.5
  • 67
    • 73749088479 scopus 로고    scopus 로고
    • Imaging brain fatigue from sustained mental workload: An ASL perfusion study of the time-on-task effect
    • Lim J, Wu WC, Wang JJ, Detre JA, Dinges DF, et al. (2010) Imaging brain fatigue from sustained mental workload: An ASL perfusion study of the time-on-task effect. Neuroimage 49: 3426-3435.
    • (2010) Neuroimage , vol.49 , pp. 3426-3435
    • Lim, J.1    Wu, W.C.2    Wang, J.J.3    Detre, J.A.4    Dinges, D.F.5
  • 68
    • 77950595917 scopus 로고    scopus 로고
    • Inter-individual differences in resting-state functional connectivity predict task-induced BOLD activity
    • Mennes M, Kelly C, Zuo XN, Di Martino A, Biswal BB, et al. (2010) Inter-individual differences in resting-state functional connectivity predict task-induced BOLD activity. NeuroImage 50: 1690-1701.
    • (2010) NeuroImage , vol.50 , pp. 1690-1701
    • Mennes, M.1    Kelly, C.2    Zuo, X.N.3    Di Martino, A.4    Biswal, B.B.5


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.