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Florin, E., Bock, E. & Baillet, S. Targeted reinforcement of neural oscillatory activity with real-time neuroimaging feedback. Neuroimage 88, 54–60 (2014). A proof-of-concept study of neurofeedback training using MEG source imaging. The data show the positive effect of training in targeted brain regions and for the specific type of brain activity that was targeted.
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Hansen, P., Kringelbach, M. & Salmelin, R. MEG: An Introduction to Methods (Oxford Univ. Press, 2010). This first textbook entirely dedicated to MEG methods is an excellent gateway for trainees and scientists intrigued by the technique.
Giraud, A.-L. & Poeppel, D. Cortical oscillations and speech processing: emerging computational principles and operations. Nat. Neurosci. 15, 511–517 (2012). An excellent review of how neuronal oscillations identified with MEG source imaging are engaged by the prosodic properties of speech at multiple time scales. The authors argue from an evolutionary perspective that oscillations participate in the foundations of speech and language processing, with the engagement of auditory and motor tuning.
Tallon-Baudry, C. On the neural mechanisms subserving consciousness and attention. Front. Psychol. 2, 397 (2012). This and the next thorough review of the neuroscience of consciousness survey both theoretical foundations and related experimental techniques. The focus and contribution of MEG are on the dynamical aspects of the timing of brain events involved in the emergence of the conscious experience.
Dehaene, S. & Changeux, J.-P. Experimental and theoretical approaches to conscious processing. Neuron 70, 200–227 (2011).
Kharkar, S. & Knowlton, R. Magnetoencephalography in the presurgical evaluation of epilepsy. Epilepsy Behav. 46, 19–26 (2015). A thorough review of the unique value of MEG in the evaluation of severe epilepsy cases.
Anderson, C.T., Carlson, C.E., Li, Z. & Raghavan, M. Magnetoencephalography in the preoperative evaluation for epilepsy surgery. Curr. Neurol. Neurosci. Rep. 14, 446 (2014).
Port, R.G. et al. Prospective MEG biomarkers in ASD: pre-clinical evidence and clinical promise of electrophysiological signatures. Yale J. Biol. Med. 88, 25–36 (2015). A review of how MEG can provide unique insight and practical markers of functional impairments in ASD.
Schnitzler, A., Timmermann, L. & Gross, J. Physiological and pathological oscillatory networks in the human motor system. J. Physiol. Paris 99, 3–7 (2006). A thorough review of how MEG imaging contributes to elucidating the brain networks affected in a variety of movement disorders. The method for dynamic imaging of coherent sources is reviewed as a means to identify and analyze cerebral oscillatory networks in health and pathology with MEG. The particular role and experimental evidence of the involvement of a cerebello-thalamo-premotor-motor cortical network are discussed in details in the context of Parkinson's disease.
Tan, H.R.M., Gross, J. & Uhlhaas, P.J. MEG-measured auditory steady-state oscillations show high test-retest reliability: a sensor and source-space analysis. Neuroimage 122, 417–426 (2015). Auditory steady-state responses represent another electrophysiological marker that is readily and robustly measured with MEG. These relatively simple signals are proposed to be used in the evaluation of neuropsychiatric conditions such as schizophrenia.
Bourguignon, M. et al. The pace of prosodic phrasing couples the listener's cortex to the reader's voice. Hum. Brain Mapp. 34, 314–326 (2013). A great demonstration of coupling between auditory speech signals and cortical activity using an ecologically valid continuous listening task. This study illustrates the capacity of MEG to produce brain maps of activity that are coherent with a peripheral, natural signal; here, throat contractions from the speech production of an individual. The temporal resolution of MEG imaging enabled the comparison between brain activity related to multiple temporal scales in speech rhythm and phrasing.
Ding, N., Melloni, L., Zhang, H., Tian, X. & Poeppel, D. Cortical tracking of hierarchical linguistic structures in connected speech. Nat. Neurosci. 19, 158–164 (2016). Another beautiful example of how MEG can track the brain activity related to the multiscale dynamics of sensory and speech signals. Results show that cortical activity at different timescales corresponded to the time course of abstract linguistic structures at different hierarchical levels, such as words, phrases and sentences.
Doelling, K.B. & Poeppel, D. Cortical entrainment to music and its modulation by expertise. Proc. Natl. Acad. Sci. USA 112, E6233–E6242 (2015). The dynamical ability of brain signals to be entrained by speech at multiple time scales corresponding to various hierarchical structures of spoken language (see previous two references) are further tested here in the context of music perception, with an emphasis on musical training. The data from musicians show that cortical entrainment is enhanced by years of musical training.
Cottereau, B. et al. Phase delays within visual cortex shape the response to steady-state visual stimulation. Neuroimage 54, 1919–1929 (2011). Tonic visual responses in occipital cortex are induced by steady-state stimulation. The study shows how such procedures enhance SNR in MEG imaging. It also allows measurement of phase differences between stimulus properties and responses at different brain sites that can be converted into time delays caused by neural signal propagation and/or processing.
Koelewijn, L., Rich, A.N., Muthukumaraswamy, S.D. & Singh, K.D. Spatial attention increases high-frequency gamma synchronisation in human medial visual cortex. Neuroimage 79, 295–303 (2013). MEG was used to explore sustained gamma activity in human early visual cortex, a hallmark of processes engaged by spatial attention. These signals are more ambiguous in EEG owing to possible confounds from muscle activity or eye saccades. Results show that stimulus- and goal-driven modulations of attention may be mediated at different frequencies within the gamma range in the early visual cortex.
Baldauf, D. & Desimone, R. Neural mechanisms of object-based attention. Science 344, 424–427 (2014). The authors used MEG and fMRI to separate rapid neuronal responses to attended and unattended objects. Delays as short as 20 ms between frontal and parahippocampal and basal posterior temporal regions were identified in a directed manner via measures of coupled oscillations. This study is a beautiful example of how MEG imaging contributes to identifying the dynamical flow of information processing in the brain.
Landau, A.N., Schreyer, H.M., van Pelt, S. & Fries, P. Distributed attention is implemented through theta-rhythmic gamma modulation. Curr. Biol. 25, 2332–2337 (2015). This article provides more compelling evidence that the phase of ongoing brain rhythms around 8 Hz that precede the onset of target stimuli of interest influences performance. Specifically, the authors test how this 8-Hz rhythm can implement the sequential sampling of multiple target locations in relation to gamma fluctuations in a visual attention task and explain the observed decrease in behavioral performances. The MEG findings suggest that theta rhythms implement an attentional sampling process that is continual and synchronized with power fluctuations in the gamma band.
Jerbi, K. et al. Coherent neural representation of hand speed in humans revealed by MEG imaging. Proc. Natl. Acad. Sci. USA 104, 7676–7681 (2007). This study is another demonstration of the powerful approach that consists in revealing the brain regions whose MEG source activity is coherent with a signal of reference. Results show that theta-band activity in sensorimotor regions is coherent with the instantaneous velocity of contralateral hand movements. The study also shows that further coherent cortico-cortical activity during movement performance spreads in a network of regions involving the supplementary motor area, dorsal parietal lobules and the ipsilateral cerebellum.
Hari, R. & Salmelin, R. Magnetoencephalography: from SQUIDs to neuroscience. Neuroimage 61, 386–396 (2012). A thorough review of MEG in neuroscience, with an emphasis on MEG's contributions to our understanding of sensory and cognitive processing, motor systems, plasticity and the neuroscience of language and social interactions.
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