The spatial relationship between event-related changes in cortical synchrony, and the haemodynamic response: an MEG-fMRI study (original) (raw)

Functional brain imaging with fMRI and MEG

2005

The work described in this thesis was performed by the author, except where indicated. All the studies were accomplished on the 3 Tesla system within the Magnetic Resonance Centre at the University of Nottingham, and the Wellcome Trust MEG Laboratory at the Aston University during the period between October 1999 and June 2005. Functional Magnetic Resonance Imaging (fMRI) and Magnetoencephalography (MEG) are two promising brain function research modalities, sensitive to the hemodynamic and electrophysiological responses respectively during brain activites. The feasibility of joint employment of both modalities was examined in both spatial and temporal domains. A somatosensory tactile stimulus was adopted to induce simple functional reaction. It was shown that a reasonable spatial correspondence between fMRI and MEG can be established. Attempts were made on MEG recordings to extract suitable aspects for temporal features matching fMRI with a method reflecting the physical principles. It was shown that the this method is capable of exposing the nature of neural electric activities, although further development is required to perfect the strategy.

Quantification and reproducibility of tracking cortical extent of activation by use of functional MR imaging and magnetoencephalography

AJNR. American journal of neuroradiology, 2000

Functional MR imaging and magnetoencephalography are commonly used to study normal cortical sensory and cognitive processing as well as a variety of disease states. The usefulness of these techniques is dependent on the reproducibility and sensitivity to change of derived measures of brain function. The purpose of this study was to compare the efficacy of functional MR imaging and magnetoencephalography as measures of the extent of cortical activity in response to a graded stimulus. Five participants underwent functional MR imaging and magnetoencephalography involving stimulation of one, two, three, and four digits of the left hand. Measurements of activation were repeated three times per participant. The cortical extent of activation was assessed for functional MR imaging by observing the number of "activated" pixels and the "amount of activation": the product of the number of activated pixels and the mean signal change. Activation was quantified for magnetoence...

Integration of Functional MRI, Structural MRI, EEG, and MEG

International Journal of Bioelectromagnetism

The combination of functional Magnetic Resonance Imaging (fMRI) with Electroencephalography (EEG) and Magnetoencephalography (MEG) source reconstruction techniques promises to add temporal resolution in the [ms] range to fMRI activation maps. Depending on the available information, different co-registration methods for merging structural Magnetic Resonance Imaging (sMRI) and fMRI coordinate systems may be useful. The usage of scanner coordinates as well as landmark-, surface-, and volume-based registration is discussed. Dipole fits can benefit from fMRI constraints: Meaningful seed points for source locations are obtained. A reconstructed dipole in the vicinity of each fMRI hotspot yields the corresponding source time course. Spatially unconstrained dipoles are then necessary to account for remaining activity. Current density reconstructions react upon fMRI constraints in two ways: Activity in the vicinity of fMRI hotspots is bundled. Remaining activity can be localized correctly, i...

Magnetoencephalography as a research tool in neuroscience: state of the art

The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry, 2006

Magnetoencephalography (MEG) is a noninvasive neuroimaging method for detecting, analyzing, and interpreting the magnetic field generated by the electrical activity in the brain. Modern hardware can capture the MEG signal at hundreds of points around the head in a snapshot lasting only a fraction of a millisecond. The sensitivity of modern hardware is high enough to permit the extraction of a clean signal generated by the brain well above the noise level of the MEG hardware. It is possible to identify signatures of superficial and often deep generators in the raw MEG signal, even in snapshots of data. In a more quantitative way, tomographic images of the electrical current density in the brain can be extracted from each snapshot of MEG signal, providing a direct correlate of coherent collective neuronal activity. A number of recent studies have scrutinized brain function in the new spatiotemporal window that real-time tomographic analysis of MEG signals has opened. The results have ...

Synchronous neural interactions assessed by magnetoencephalography: a functional biomarker for brain disorders

Journal of Neural Engineering, 2007

We report on a test to assess the dynamic brain function at high temporal resolution using magnetoencephalography (MEG). The essence of the test is the measurement of the dynamic synchronous neural interactions, an essential aspect of the brain function. MEG signals were recorded from 248 axial gradiometers while 142 human subjects fixated a spot of light * Contribution by the authors: Designed research (APG); acquired data (AAA, IGK, FJPL, ACL, SML,

Comparison of BOLD fMRI and MEG characteristics to vibrotactile stimulation

NeuroImage, 2003

The characteristics of blood oxygenation level-dependent (BOLD) fMRI and magnetoencephalographic (MEG) responses to vibrotactile stimuli in humans were studied and compared. The stimuli, presented with interstimulus intervals (ISIs) ranging from 1 to 5 s, yielded highly reproducible MEG responses, with current dipoles in the primary somatosensory (SI) cortex in all subjects. BOLD fMRI responses to similar stimuli showed substantial intrasubject variation in the activation sites around the SI cortex. BOLD responses were detected in all subjects in the secondary somatosensory (SII) cortices as well, with comparable BOLD response amplitudes to those in the SI cortex. Current dipoles, used to model the MEG signals, were stronger at longer ISIs than shorter ISIs. The BOLD response amplitudes did not show a similar dependence on ISI, but the activated brain area was larger when longer ISIs or longer stimuli were applied. Our results support the view that combined use of brain mapping methods provides complementary information and should be considered in functional brain examinations.