Measuring electrophysiological connectivity by power envelope correlation: A technical review on MEG methods

Physics in Medicine and Biology

Volumn 60, Issue 21, 2015, Pages R271-R295

  O'Neill, George C ^a   Barratt, Eleanor L ^a   Hunt, Benjamin A E ^a   Tewarie, Prejaas K ^a   Brookes, Matthew J ^a  

^a UNIVERSITY OF NOTTINGHAM   (United Kingdom)

Author keywords

beamformer; functional connectivity; leakage; magnetoencephalography; MEG; networks

Indexed keywords

BRAIN MAPPING; ELECTROPHYSIOLOGY; INVERSE PROBLEMS; LEAKAGE (FLUID); MAGNETOENCEPHALOGRAPHY; NETWORKS (CIRCUITS);

BEAM FORMERS; CURRENT PROCESSING; ENVELOPE CORRELATION; FUNCTIONAL CONNECTIVITY; INFORMATION CONTENTS; NETWORK CONNECTIVITY; NETWORK COORDINATIONS; TEMPORAL RESOLUTION;

BRAIN;

BRAIN; HUMAN; MAGNETOENCEPHALOGRAPHY; NERVE CELL NETWORK; NEUROIMAGING; PHYSIOLOGY; PROCEDURES;

BRAIN; HUMANS; MAGNETOENCEPHALOGRAPHY; NERVE NET; NEUROIMAGING;

EID: 84946067009     PISSN: 00319155     EISSN: 13616560     Source Type: Journal    
DOI: 10.1088/0031-9155/60/21/R271     Document Type: Review

References (121)

1. Allen E A, Damaraju E, Plis S M, Erhardt E B, Eichele T and Calhoun V D 2014 Tracking whole-brain connectivity dynamics in the resting state Cereb. Cortex 24 663-76
2. Allen G et al 2007 Reduced hippocampal functional connectivity in Alzheimer disease Arch. Neurol. 64 1482-7
3. Baker A P, Brookes M J, Rezek I A, Smith S M, Behrens T, Probert Smith P J and Woolrich M 2014 Fast transient networks in spontaneous human brain activity eLife 3 e01867
4. Baker A P, Luckhoo H, Brookes M J, Smith P and Woolrich M 2012 Investigating the temporal dynamics of resting state brain connectivity using magnetoencephalography Organization of Human Brain Mapping
5. Bassett D S, Meyer-Lindenberg A, Achard S, Duke T and Bullmore E 2006 Adaptive reconfiguration of fractal small-world human brain functional networks Proc. Natl Acad. Sci. 103 19518-23
6. Bauer M, Stenner M P, Friston K J and Dolan R J 2014 Attentional modulation of alpha/beta and gamma oscillations reflect functionally distinct processes J. Neurosci. 34 16117-25
7. Beckmann C F, DeLuca M, Devlin J T and Smith S M 2005 Investigations into resting-state connectivity using independent component analysis Phil. Trans. R. Soc. B 360 1001-13
8. Berger H 1929 Über das Elektrenkephalogramm des Menschen Arch. Psychiat. Nerven. 87 527-70
9. Birn R M 2012 The role of physiological noise in resting-state functional connectivity Neuroimage 62 864-70
10. Biswal B, Yetkin F Z, Haughton V M and Hyde J S 1995 Functional connectivity in the motor cortex of resting human brain using echo-planar MRI Magn. Reson. Med. 34 537-41
11. Brookes M J, Gibson A M, Hall S D, Furlong P L, Barnes G R, Hillebrand A, Singh K D, Holliday I E, Francis S T and Morris P G 2005 GLM-beamformer method demonstrates stationary field, alpha ERD and gamma ERS co-localisation with fMRI BOLD response in visual cortex Neuroimage 26 302-8
12. Brookes M J, Hale J R, Zumer J M, Stevenson C M, Francis S T, Barnes G R, Owen J P, Morris P G and Nagarajan S S 2011a Measuring functional connectivity using MEG: methodology and comparison with fcMRI Neuroimage 56 1082-104
13. Brookes M J, Liddle E B, Hale J R, Woolrich M W, Luckhoo H, Liddle P F and Morris P G 2012a Task induced modulation of neural oscillations in electrophysiological brain networks Neuroimage 63 1918-30
14. Brookes M J, O'Neill G C, Hall E L, Woolrich M W, Baker A, Palazzo Corner S, Robson S E, Morris P G and Barnes G R 2014a Measuring temporal, spectral and spatial changes in electrophysiological brain network connectivity Neuroimage 91 282-99
15. Brookes M J, Stevenson C M, Barnes G R, Hillebrand A, Simpson M I, Francis S T and Morris P G 2007 Beamformer reconstruction of correlated sources using a modified source model NeuroImage 34 1454-65
16. Brookes M J, Vrba J, Robinson S E, Stevenson C M, Peters A M, Barnes G R, Hillebrand A and Morris P G 2008 Optimising experimental design for MEG beamformer imaging Neuroimage 39 1788-802
17. Brookes M J, Woolrich M, Luckhoo H, Price D, Hale J R, Stephenson M C, Barnes G R, Smith S M and Morris P G 2011b Investigating the electrophysiological basis of resting state networks using magnetoencephalography Proc. Natl Acad. Sci. USA 108 16783-8
18. Brookes M J, Woolrich M W and Barnes G R 2012b Measuring functional connectivity in MEG: a multivariate approach insensitive to linear source leakage Neuroimage 63 910-20
19. Brookes M J, Woolrich M W and Price D 2014b Magnetoencephalography ed S Supek and C J Aine (Berlin: Springer) pp 321-58
20. Chang C and Glover G H 2010 Time-frequency dynamics of resting-state brain connectivity measured with fMRI Neuroimage 50 81-98
21. Cohen D 1968 Magnetoencephalography: evidence of magnetic fields produced by alpha-rhythm currents Science 161 784-6
22. Cohen D 1972 Magnetoencephalography: detection of the brain's electrical activity with a superconducting magnetometer Science 175 664-6
23. Colclough G L, Brookes M J, Smith S M and Woolrich M W 2015 A symmetric multivariate leakage correction for MEG connectomes Neuroimage 117 439-48
24. Corbetta M 1998 Frontoparietal cortical networks for directing attention and the eye to visual locations: identical, independent, or overlapping neural systems? Proc. Natl Acad. Sci. USA 95 831-8
25. Dalal S S, Sekihara K and Nagarajan S S 2006 Modified beamformers for coherent source region suppression IEEE Trans. BioMed. Eng. 53 1357-63
26. Dale A M, Liu A K, Fischl B R, Buckner R L, Belliveau J W, Lewine J D and Halgren E 2000 Dynamic statistical parametric mapping: combining fMRI and MEG for high-resolution imaging of cortical activity Neuron 26 55-67
27. de Pasquale F et al 2010 Temporal dynamics of spontaneous MEG activity in brain networks Proc. Natl Acad. Sci. USA 107 6040-5
28. Deco G, Jirsa V K and McIntosh A R 2011 Emerging concepts for the dynamical organization of resting-state activity in the brain Nat. Rev. Neurosc. 12 43-56
29. Diwakar M, Tal O, Liu T T, Harrington D L, Srinivasan R, Muzzatti L, Song T, Theilmann R J, Lee R R and Huang M X 2011 Accurate reconstruction of temporal correlation for neuronal sources using the enhanced dual-core MEG beamformer Neuroimage 56 1918-28
30. Engel A K, Gerloff C, Hilgetag C C and Nolte G 2013 Intrinsic coupling modes: multiscale interactions in ongoing brain activity Neuron 80 867-86
31. Ewald A, Marzetti L, Zappasodi F, Meinecke F C and Nolte G 2012 Estimating true brain connectivity from EEG/MEG data invariant to linear and static transformations in sensor space Neuroimage 60 476-88
32. Florin E and Baillet S 2015 The brain's resting-state activity is shaped by synchronized cross-frequency coupling of neural oscillations Neuroimage 111 26-35
33. Fox M D and Raichle M E 2007 Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging Nat. Rev. Neurosci. 8 700-11
34. Fox M D, Snyder A Z, Vincent J L, Corbetta M, Van Essen D C and Raichle M E 2005 The human brain is intrinsically organized into dynamic, anticorrelated functional networks Proc. Natl Acad. Sci. USA 102 9673-8
35. Freeman W J 2004 Origin, structure, and role of background EEG activity. Part 1. Analytic amplitude Clin. Neurophysiol. 115 2077-88
36. Friston K J 1998 The disconnection hypothesis Schizophrenia Res. 30 115-25
37. Fuchs M, Wagner M, Kohler T and Wischmann H A 1999 Linear and nonlinear current density reconstructions J. Clin. Neurophysiol. 16 267-95
38. Gow D W Jr, Segawa J A, Ahlfors S P and Lin F H 2008 Lexical influences on speech perception: a Granger causality analysis of MEG and EEG source estimates Neuroimage 43 614-23
39. Grady C L, Furey M L, Pietrini P, Horwitz B and Rapoport S I 2001 Altered brain functional connectivity and impaired short-term memory in Alzheimer's disease Brain 124 739-56
40. Greenblatt R E, Ossadtchi A and Pflieger M E 2005 Local linear estimators for the bioelectromagnetic inverse problem IEEE T Signal Process 53 3403-12
41. Gross J, Kujala J, Hamalainen M, Timmermann L, Schnitzler A and Salmelin R 2001 Dynamic imaging of coherent sources: studying neural interactions in the human brain Proc. Natl Acad. Sci. USA 98 694-9
42. Gross J, Timmermann L, Kujala J, Dirks M, Schmitz F, Salmelin R and Schnitzler A 2002 The neural basis of intermittent motor control in humans Proc. Natl Acad. Sci. USA 99 2299-302
43. Hacker C D, Perlmutter J S, Criswell S R, Ances B M and Snyder A Z 2012 Resting state functional connectivity of the striatum in Parkinson's disease Brain 135 3699-711
44. Hadamard J 1902 Sur les problèmes aux dérivés partielles et leur signification physique Princeton Univ. Bull. 13 49-52
45. Hall E L, Robson S E, Morris P G and Brookes M J 2014 The relationship between MEG and fMRI Neuroimage 102 80-91
46. Hall E L, Woolrich M W, Thomaz C E, Morris P G and Brookes M J 2013 Using variance information in magnetoencephalography measures of functional connectivity Neuroimage 67 203-12
47. Hämäläinen M, Hari R, Ilmoniemi R, Knuutila J and Lounasmaa O 1993 Magnetoencephalography - theory, instrumentation, and applications to noninvasive studies of the working human brain Rev. Mod. Phys. 65 413-97
48. Hamalainen M S and Ilmoniemi R J 1994 Interpreting magnetic fields of the brain: minimum norm estimates Med. Biol. Eng. Comput. 32 35-42
49. Haneef Z, Lenartowicz A, Yeh H J, Levin H S, Engel J Jr and Stern J M 2014 Functional connectivity of hippocampal networks in temporal lobe epilepsy Epilepsia 55 137-45
50. Hansen E C, Battaglia D, Spiegler A, Deco G and Jirsa V K 2015 Functional connectivity dynamics: modeling the switching behavior of the resting state Neuroimage 105 525-35
51. Hawellek D J, Hipp J F, Lewis C M, Corbetta M and Engel A K 2011 Increased functional connectivity indicates the severity of cognitive impairment in multiple sclerosis Proc. Natl Acad. Sci. USA 108 19066-71
52. Hillebrand A, Barnes G R, Bosboom J L, Berendse H W and Stam C J 2012 Frequency-dependent functional connectivity within resting-state networks: an atlas-based MEG beamformer solution Neuroimage 59 3909-21
53. Hillebrand A, Singh K D, Holliday I E, Furlong P L and Barnes G R 2005 A new approach to neuroimaging with magnetoencephalography Hum. Brain Mapp. 25 199-211
54. Hipp J F, Hawellek D J, Corbetta M, Siegel M and Engel A K 2012 Large-scale cortical correlation structure of spontaneous oscillatory activity Nat. Neurosci. 15 884-90
55. Hipp J F and Siegel M 2015 BOLD fMRI correlation reflects frequency-specific neuronal correlation Curr. Biol. 25 1368-74
56. Hutchison R M et al 2013 Dynamic functional connectivity: promise, issues, and interpretations Neuroimage 80 360-78
57. Ioannides A A, Liu L C, Kwapien J, Drozdz S and Streit M 2000 Coupling of regional activations in a human brain during an object and face affect recognition task Hum. Brain Mapp. 11 77-92
58. Jerbi K, Lachaux J P, N'Diaye K, Pantazis D, Leahy R M, Garnero L and Baillet S 2007 Coherent neural representation of hand speed in humans revealed by MEG imaging Proc. Natl Acad. Sci. USA 104 7676-81
59. Kessler D, Angstadt M, Welsh R C and Sripada C 2014 Modality-spanning deficits in attention-deficit/hyperactivity disorder in functional networks, gray matter, and white matter J. Neurosci. 34 16555-66
60. Kiebel S J, Tallon-Baudry C and Friston K J 2005 Parametric analysis of oscillatory activity as measured with EEG/MEG Hum. Brain Mapp. 26 170-7
61. Le Van Quyen M, Foucher J, Lachaux J-P, Rodriguez E, Lutz A, Martinerie J and Varela F J 2001 Comparison of Hilbert transform and wavelet methods for the analysis of neuronal synchrony J. Neurosci. Methods 111 83-98
62. Leavitt V, Wylie G, Girgis P, DeLuca J and Chiaravalloti N 2014 Increased functional connectivity within memory networks following memory rehabilitation in multiple sclerosis Brain Imaging Behav. 8 394-402
63. Liu Z, Fukunaga M, de Zwart J A and Duyn J H 2010 Large-scale spontaneous fluctuations and correlations in brain electrical activity observed with magnetoencephalography Neuroimage 51 102-11
64. Logothetis N K, Pauls J, Augath M, Trinath T and Oeltermann A 2001 Neurophysiological investigation of the basis of the fMRI signal Nature 412 150-7
65. Lowdin P O 1950 On the non-orthogonality problem connected with the use of atomic wave functions in the theory of molecules and crystals J. Chem. Phys. 18 365-75
66. Luckhoo H, Hale J R, Stokes M G, Nobre A C, Morris P G, Brookes M J and Woolrich M W 2012 Inferring task-related networks using independent component analysis in magnetoencephalography Neuroimage 62 530-41
67. Maccotta L, He B J, Snyder A Z, Eisenman L N, Benzinger T L, Ances B M, Corbetta M and Hogan R E 2013 Impaired and facilitated functional networks in temporal lobe epilepsy Neuroimage Clin. 2 862-72
68. Maldjian J A, Davenport E M and Whitlow C T 2014 Graph theoretical analysis of resting-state MEG data: identifying interhemispheric connectivity and the default mode Neuroimage 96 88-94
69. Marzetti L, Della Penna S, Snyder A Z, Pizzella V, Nolte G, de Pasquale F, Romani G L and Corbetta M 2013 Frequency specific interactions of MEG resting state activity within and across brain networks as revealed by the multivariate interaction measure Neuroimage 79 172-83
70. Mayer I 2002 On Lowdin's method of symmetric orthogonalization Int. J. Quantum Chem. 90 63-5
71. Moradi F, Liu L C, Cheng K, Waggoner R A, Tanaka K and Ioannides A A 2003 Consistent and precise localization of brain activity in human primary visual cortex by MEG and fMRI Neuroimage 18 595-609
72. Mukamel R, Gelbard H, Arieli A, Hasson U, Fried I and Malach R 2005 Coupling between neuronal firing, field potentials, and FMRI in human auditory cortex Science 309 951-4
73. Murphy K, Birn R M and Bandettini P A 2013 Resting-state fMRI confounds and cleanup Neuroimage 80 349-59
74. Muthukumaraswamy S D and Singh K D 2008 Spatiotemporal frequency tuning of BOLD and gamma band MEG responses compared in primary visual cortex Neuroimage 40 1552-60
75. Nolte G, Bai O, Wheaton L, Mari Z, Vorbach S and Hallett M 2004 Identifying true brain interaction from EEG data using the imaginary part of coherency Clin. Neurophysiol. 115 2292-307
76. Nolte G, Ziehe A, Nikulin V V, Schlogl A, Kramer N, Brismar T and Muller K R 2008 Robustly estimating the flow direction of information in complex physical systems Phys. Rev. Lett. 100 234101
77. Nunez P L and Srinivasan R 2006 Electric Fields of the Brain: the Neurophysics of Eeg (New York: Oxford University Press)
78. O'Neill G C, Bauer M, Woolrich M W, Morris P G, Barnes G R and Brookes M J 2015 Dynamic recruitment of resting state sub-networks Neuroimage 115 85-95
79. O'Neill G C, Hall E, Palazzo Corner S, Morris P G and Brookes M J 2013 A Comparison of beamformer and minimim norm soultions for meg network connectivity mapping Organization of Human Brain Mapping
80. Palaniyappan L and Liddle P F 2012 Does the salience network play a cardinal role in psychosis? An emerging hypothesis of insular dysfunction J. Psychiatry Neurosci. 37 17-27
81. Palva J M, Monto S, Kulashekhar S and Palva S 2010 Neuronal synchrony reveals working memory networks and predicts individual memory capacity Proc. Natl Acad. Sci. USA 107 7580-5
82. Pascual-Marqui R D 2002 Standardized low-resolution brain electromagnetic tomography (sLORETA): technical details Methods Find. Exp Clin. Pharmacol. 24 5-12
83. Ponce-Alvarez A, Deco G, Hagmann P, Romani G L, Mantini D and Corbetta M 2015 Resting-state temporal synchronization networks emerge from connectivity topology and heterogeneity PLoS Comput. Biol. 11 e1004100
84. Popescu M, Popescu E A, Chan T, Blunt S D and Lewine J D 2008 Spatio-temporal reconstruction of bilateral auditory steady-state responses using MEG beamformers IEEE Trans. Biomed. Eng. 55 1092-102
85. Prendergast G, Green G G and Hymers M 2013 A robust implementation of a kurtosis beamformer for the accurate identification of epileptogenic foci Clin. Neurophysiol. 124 658-66
86. Prichard D and Theiler J 1994 Generating surrogate data for time-series with several simultaneously measured variables Phys. Rev. Lett. 73 951-4
87. Puts N A, Edden R A, Evans C J, McGlone F and McGonigle D J 2011 Regionally specific human GABA concentration correlates with tactile discrimination thresholds J. Neurosci. 31 16556-60
88. Raichle M E, MacLeod A M, Snyder A Z, Powers W J, Gusnard D A and Shulman G L 2001 A default mode of brain function Proc. Natl Acad. Sci. USA 98 676-82
89. Robinson S E and Vrba J 1998 Functional neuroimaging by synthetic aperture magnetometry (SAM) Recent Advances in Biomagnetism ed T Yashimoto, M Kotani, S Kuriki, H Karibe and N Nakasato (Sendai: Tohoku University Press) pp 302-5
90. Schnitzler A and Gross J 2005 Functional connectivity analysis in magnetoencephalography Int. Rev. Neurobiol. 68 173-95
91. Schoffelen J M and Gross J 2009 Source connectivity analysis with MEG and EEG Hum. Brain Mapp. 30 1857-65
92. Scholvinck M L, Leopold D A, Brookes M J and Khader P H 2013 The contribution of electrophysiology to functional connectivity mapping Neuroimage 80 297-306
93. Sekihara K, Hild K E and Nagarajan S S 2006 A novel adaptive beamformer for MEG source reconstruction effective when large background brain activities exist IEEE Trans Biomed Eng. 53 1755-64
94. Sekihara K and Nagarajan S S 2008 Adaptive Spatial Filters for Electromagnetic Brain Imaging (Berlin: Springer)
95. Sekihara K, Nagarajan S S, Poeppel D, Marantz A and Miyashita Y 2001 Reconstructing spatio-temporal activities of neural sources using an MEG vector beamformer technique IEEE Transactions Biomed. Eng. 48 760-71
96. Singer W 1999 Neuronal synchrony: a versatile code for the definition of relations? Neuron 24 49-65, 111-25
97. Singh K D, Barnes G R, Hillebrand A, Forde E M and Williams A L 2002 Task-related changes in cortical synchronization are spatially coincident with the hemodynamic response Neuroimage 16 103-14
98. Smith S M et al 2009 Correspondence of the brain's functional architecture during activation and rest Proc. Natl Acad. Sci. USA 106 13040-5
99. Smith S M et al 2012 Temporally-independent functional modes of spontaneous brain activity Proc. Natl Acad. Sci. USA 109 3131-6
100. Stam C J 2004 Functional connectivity patterns of human magnetoencephalographic recordings: a 'small-world'network? Neurosci. Lett. 355 25-8
101. Stam C J, Nolte G and Daffertshofer A 2007 Phase lag index: assessment of functional connectivity from multi channel EEG and MEG with diminished bias from common sources Hum. Brain Mapping 28 1178-93
102. Stevenson C M, Brookes M J and Morris P G 2011 β-Band correlates of the fMRI BOLD response Hum. Brain Mapp. 32 182-97
103. Stevenson C M, Wang F, Brookes M J, Zumer J M, Francis S T and Morris P G 2012 Paired pulse depression in the somatosensory cortex: associations between MEG and BOLD fMRI Neuroimage 59 2722-32
104. Stockwell R G, Mansinha L and Lowe R P 1996 Localization of the complex spectrum: the S transform IEEE T Signal Process 44 998-1001
105. Tass P, Rosenblum M G, Weule J, Kurths J, Pikovsky A, Volkmann J, Schnitzler A and Freund H J 1998 Detection of n:m phase locking from noisy data: application to magnetoencephalography Phys. Rev. Lett. 81 3291-4
106. Tewarie P, Hillebrand A, van Dellen E, Schoonheim M M, Barkhof F, Polman C H, Beaulieu C, Gong G, van Dijk B W and Stam C J 2014a Structural degree predicts functional network connectivity: a multimodal resting-state fMRI and MEG study Neuroimage 97 296-307
107. Tewarie P et al 2014b Disruption of structural and functional networks in long-standing multiple sclerosis Hum. Brain Mapp. 35 5946-61
108. Tewarie P, Schoonheim M M, Stam C J, van der Meer M L, van Dijk B W, Barkhof F, Polman C H and Hillebrand A 2013 Cognitive and clinical dysfunction, altered MEG resting-state networks and thalamic atrophy in multiple sclerosis PloS One 8 e69318
109. Tomasi D and Volkow N D 2012 Abnormal functional connectivity in children with attention-deficit/hyperactivity disorder Biol. Psychiatry 71 443-50
110. Tong Y, Hocke L M, Fan X, Janes A C and Frederick B 2015 Can apparent resting state connectivity arise from systemic fluctuations? Front. Hum. Neurosci. 9 285
111. Troebinger L, Lopez J D, Lutti A, Bestmann S and Barnes G 2014 Discrimination of cortical laminae using MEG Neuroimage 102 885-93
112. Van Drongelen W, Yuchtman M, Van Veen B and Van Huffelen A 1996 A spatial filtering technique to detect and localize multiple sources in the brain Brain Topogr. 9 39-49
113. Van Veen B D, van Drongelen W, Yuchtman M and Suzuki A 1997 Localization of brain electrical activity via linearly constrained minimum variance spatial filtering IEEE Trans. Biomed. Eng. 44 867-80
114. Vinck M, Oostenveld R, van Wingerden M, Battaglia F and Pennartz C M 2011 An improved index of phase-synchronization for electrophysiological data in the presence of volume-conduction, noise and sample-size bias Neuroimage 55 1548-65
115. Wang K, Liang M, Wang L, Tian L, Zhang X, Li K and Jiang T 2007 Altered functional connectivity in early Alzheimer's disease: a resting-state fMRI study Hum. Brain Mapp. 28 967-78
116. Wens V et al 2014a Inter- and intra-subject variability of neuromagnetic resting state networks Brain Topogr. 27 620-34
117. Wens V, Mary A, Bourguignon M, Goldman S, Marty B, Beeck M O, Bogaert P V, Peigneux P and Tiege X D 2014b About the electrophysiological basis of resting state networks Clin. Neurophysiol. 125 1711-3
118. Wibral M, Lizier J T, Vogler S, Priesemann V and Galuske R 2014 Local active information storage as a tool to understand distributed neural information processing Front. Neuroinform. 8 1
119. Winterer G, Carver F W, Musso F, Mattay V, Weinberger D R and Coppola R 2007 Complex relationship between BOLD signal and synchronization/desynchronization of human brain MEG oscillations Hum. Brain Mapp. 28 805-16
120. Zimmerman J E, Thiene P and Harding J T 1970 Design and operation of stable rf-biased superconducting point-contact quantum devices, and a note on properties of perfectly clean metal contacts J. Appl. Phys. 41 1572
121. Zumer J M, Brookes M J, Stevenson C M, Francis S T and Morris P G 2010 Relating BOLD fMRI and neural oscillations through convolution and optimal linear weighting NeuroImage 49 1479-89