[Eeglablist] Can amygdala activity be detected on the scalp?

Darren Weber dweber at radmail.ucsf.edu
Wed Jan 4 12:35:04 PST 2006


Ionnides etal. has published recent work on these problems, including 
dynamic imaging of cerebellum, a "deep" structure relative to the 
cortex, in some respects it may be deeper than the amygdala.  I think 
this paper discusses some of the issues related to your question, but 
consider some technical differences between EEG/MEG (see below):


@ARTICLE{Ioannides2004,
  author = {Andreas A Ioannides and Vahe Poghosyan and Jürgen Dammers 
and Marcus
        Streit},
  title = {Real-time neural activity and connectivity in healthy individuals
        and schizophrenia patients.},
  journal = {Neuroimage},
  year = {2004},
  volume = {23},
  pages = {473--482},
  number = {2},
  month = {Oct},
  abstract = {Processing of facial information is distributed across 
several brain
        regions, as has been shown recently in many neuroimaging studies.
        Disturbances in accurate face processing have been repeatedly 
demonstrated
        in different stages of schizophrenia. Recently, 
electroencephalography
        (EEG) and tomographic analysis of average magnetoencephalographic
        (MEG) data were used to define the latencies of significant regional
        brain activations in healthy and schizophrenic subjects elicited
        during the recognition of facial expression of emotions. The current
        study re-examines these results using tomographic analysis of single
        trial MEG data. In addition to the areas identified by the analysis
        of the average MEG data, statistically significant activity is 
identified
        in several other areas, including a sustained increase in the right
        amygdala activity in response to emotional faces in schizophrenic
        subjects. The single trial analysis demonstrated that the reduced
        activations identified from the average MEG signal of schizophrenic
        subjects is due to high variability across single trials rather than
        reduced activity in each single trial. In control subjects, direct
        measures of linkage demonstrate distinct stages of processing of
        emotional faces within well-defined network of brain regions. 
Activity
        in each node of the network, confined to 30 to 40 ms latency 
windows,
        is linked to earlier and later activations of the other nodes of
        the network. In schizophrenic subjects, no such well-defined stages
        of processing were observed. Instead, the activations, although 
strong
        were poorly linked to each other, managing only isolated links 
between
        pairs of areas.},
  doi = {10.1016/j.neuroimage.2004.06.023},
  keywords = {Adult, Age of Onset, Brain, Brain Mapping, Cerebellum, 
Computer Systems,
        Emotions, Face, Female, Humans, Magnetoencephalography, Male, Mental
        Processes, Neural Pathways, Non-U.S. Gov't, Photic Stimulation, 
Psychiatric
        Status Rating Scales, Recognition (Psychology), Research Support,
        Schizophrenia, Schizophrenic Psychology, 15488397},
  pii = {S1053-8119(04)00332-5},
  pmid = {15488397},
  url = {http://dx.doi.org/10.1016/j.neuroimage.2004.06.023},
}



@ARTICLE{Ioannides2005a,
  author = {Andreas A Ioannides and Peter B C Fenwick},
  title = {Imaging cerebellum activity in real time with 
magnetoencephalographic
        data.},
  journal = {Prog Brain Res},
  year = {2005},
  volume = {148},
  pages = {139--150},
  abstract = {The cerebellum has traditionally been associated with 
motor movements
        but recent studies suggest its involvement with fine timing, sensory
        analysis and cognition. Much of the new data comes from neuroimaging
        techniques such as fMRI and PET, which have high spatial resolution
        and show that for even simple stimuli many cerebellar and cortical
        areas are involved. We use examples from recent studies to 
demonstrate
        that magnetic field tomography (MFT) offers a new and powerful tool
        for studying cerebellar function through real time localization of
        cortical, brainstem and cerebellar activations over timescales 
ranging
        from a fraction of a millisecond to seconds, minutes and hours. The
        examples include demonstration of cerebellar activations along 
well-established
        anatomical pathways during saccades and the visualization of the
        ascending medullar volley after median nerve stimulation. MFT 
analysis
        of single trial MEG signals elicited by the presentation of faces
        in emotion and object recognition tasks, show changes in cerebellar
        activation between schizophrenics and normal subjects in agreement
        with proposals for disturbed cerebellar function in schizophrenia.
        The ability of MFT to identify cerebellar, brainstem and cortical
        activations in real time can add new insights about dynamics of 
brain
        activity to the recent findings about cerebellar function from PET
        and fMRI.},
  doi = {10.1016/S0079-6123(04)48012-1},
  keywords = {Brain Mapping, Cerebellum, Computer Systems, Humans, 
Magnetoencephalography,
        Schizophrenia, 15661187},
  pii = {S0079612304480121},
  pmid = {15661187},
  url = {http://dx.doi.org/10.1016/S0079-6123(04)48012-1},
}








With regard to technical details on EEG / MEG sensitivity, see also:



@ARTICLE{HillebrandBarnes2002,
  author = {Hillebrand, A. and Barnes, G. R.},
  title = {A Quantitative Assessment of the Sensitivity of Whole-Head {MEG}
        to Activity in the Adult Human Cortex},
  journal = {NeuroImage},
  year = {2002},
  volume = {16},
  pages = {638-650},
  number = {3},
  month = {Jul},
  abstract = {{MagnetoEncephaloGraphy ({MEG}) relies on the detection of 
cortical
        current flow by measurement of the associated magnetic field outside
        the head. The amplitude of this magnetic field depends strongly on
        the depth of the electrical brain activity. Additionally, radially
        orientated sources are magnetically silent in a concentrically 
homogeneous
        volume conductor, giving rise to the anecdotal assumptions that MEG
        is insensitive to both deep and gyral sources. Utilising cortical
        surfaces extracted from Magnetic Resonance Images (MRIs) of two 
adult
        brains we constructed all possible single source elements and 
examined
        the proportion of active neocortex that is actually detectable with
        a whole-head MEG system. We identified those electrically active
        regions to which MEG is maximally sensitive by analytically 
computing
        the probability of detecting a source within a specified confidence
        volume. Our findings show that source depth, and not orientation,
        is the main factor that compromises the sensitivity of MEG to 
activity
        in the adult human cortex. There are thin strips (~2 mm wide) of
        poor resolvability at the crests of gyri; however, these strips 
account
        for only a relatively small proportion of the cortical area and are
        abutted by elements with nominal tangential component yet high 
resolvability
        due to their proximity to the sensor array. Finally, we varied the
        extent of the patches of cortical activity, showing that small 
patches
        have a small net-current moment and are therefore less visible 
whereas
        large patches have a strong net-current moment, are generally more
        visible to the MEG system, yet are less appropriately modelled as
        single dipoles.}},
  keywords = {magnetoencephalography; MEG; cortical surface model; 
detection probability;
        sensitivity; radial; cortical patch.},
  url = 
{http://www.sciencedirect.com/science/article/B6WNP-46HDMPV-8/2/f62305a8d87d5b2934d923352e203175},
}


@ARTICLE{MalmivuoSuihkoEskola1997,
  author = {Malmivuo, J. and Suihko, V. and Eskola, H.},
  title = {Sensitivity distributions of {EEG} and {MEG} measurements.},
  journal = {IEEE Transactions On Biomedical Engineering},
  year = {1997},
  volume = {44},
  pages = {196--208},
  number = {3},
  month = {Mar},
  abstract = {It is generally believed that because the skull has low 
conductivity
        to electric current but is transparent to magnetic fields, the 
measurement
        sensitivity of the magnetoencephalography (MEG) in the brain region
        should be more concentrated than that of the electroencephalography
        (EEG). It is also believed that the information recorded by these
        techniques is very different. If this were indeed the case, it might
        be possible to justify the cost of MEG instrumentation which is at
        least 25 times higher than that of EEG instrumentation. The 
localization
        of measurement sensitivity using these techniques was evaluated 
quantitatively
        in an inhomogeneous spherical head model using a new concept called
        half-sensitivity volume (HSV). It is shown that the planar 
gradiometer
        has a far smaller HSV than the axial gradiometer. However, using
        the EEG it is possible to achieve even smaller HSV's than with 
whole-head
        planar gradiometer MEG devices. The micro-superconducting quantum
        interference device (SQUID) MEG device does have HSV's comparable
        to those of the EEG. The sensitivity distribution of planar 
gradiometers,
        however, closely resembles that of dipolar EEG leads and, therefore,
        the MEG and EEG record the electric activity of the brain in a very
        similar way.},
  doi = {10.1109/10.554766},
  keywords = {Adult, Algorithms, Anatomic, Anisotropy, Biological, 
Brain, Cerebral
        Cortex, Computer Simulation, Computer-Assisted, Coronary Disease,
        Coronary Vessels, Electric Conductivity, Electrocardiography, 
Electrodes,
        Electroencephalography, Equipment Design, Exercise Test, Female,
        Head, Heart Rate, Humans, Image Processing, Magnetic Resonance 
Imaging,
        Magnetoencephalography, Male, Middle Aged, Models, Myocardial 
Ischemia,
        Neurological, Non-U.S. Gov't, ROC Curve, Reproducibility of Results,
        Research Support, Sensitivity and Specificity, Skull, 9216133},
  pdf = {MEG_EEG_sensitivity_MalmivuoSuihkoEskola1997.pdf},
  pmid = {9216133},
  url = {http://dx.doi.org/10.1109/10.554766},
}






Combinations of EEG/MEG can help, see:


@ARTICLE{FuchsWagnerWischmann98,
  author = {Fuchs, Manfred and Wagner, Michael and Wischmann, Hans-Aloys and
        K{\"{o}}hler, Thomas and Thei{\ss}en, Annette and Drenckhahn, Ralf
        and Buchner, Helmut},
  title = {Improving source reconstructions by combining bioelectric and 
biomagnetic
        data},
  journal = {Electroencephalography And Clinical Neurophysiology},
  year = {1998},
  volume = {107},
  pages = {93-111},
  number = {2},
  abstract = {Objectives: A framework for combining bioelectric and 
biomagnetic
        data is presented. The data are transformed to signal-to-noise 
ratios
        and reconstruction algorithms utilizing a new regularization 
approach
        are introduced. Methods: Extensive simulations are carried out for
        19 different EEG and MEG montages with radial and tangential test
        dipoles at different eccentricities and noise levels. The methods
        are verified by real SEP/SEF measurements. A common realistic volume
        conductor is used and the less well known in vivo conductivies are
        matched by calibration to the magnetic data. Single equivalent 
dipole
        fits as well as spatio-temporal source models are presented for 
single
        and combined modality evaluations and overlaid to anatomic MR 
images.
        Results: Normalized sensitivity and dipole resolution profiles of
        the different EEG/MEG acquisition systems are derived from the 
simulated
        data. The methods and simulations are verified by simultaneously
        measured somatosensory data. Conclusions: Superior spatial 
resolution
        of the combined data studies is revealed, which is due to the 
complementary
        nature of both modalities and the increased number of sensors. A
        better understanding of the underlying neuronal processes can be
        achieved, since an improved differentiation between quasi-tangential
        and quasi-radial sources is possible},
  keywords = {Electroencephalogram, Magnetoencephalogram, SEP, SEF, 
Source reconstruction,
        Regularization},
}



@ARTICLE{DaleSereno1993,
  author = {Dale, Anders M. and Sereno, Marty I. },
  title = {Improved localization of cortical activity by combining {EEG} and
        {MEG} with {MRI} cortical surface reconstruction: A linear 
approach},
  journal = {Journal of Cognitive Neuroscience},
  year = {1993},
  volume = {5},
  pages = {162--176},
  number = {2},
  abstract = {We describe a comprehensive linear approach to the problem 
of imaging
        brain activity with high temporal as well as spatial resolution 
based
        on combining EEG and MEG data with anatomical constraints derived
        from MRI images. The ?inverse problem? of estimating the 
distribution
        of dipole strengths over the cortical surface is highly 
underdetermined,
        even given closely spaced EEG and MEG recordings. We have obtained
        much better solutions to this problem by explicitly incorporating
        both local cortical orientation as well as spatial covariance of
        sources and sensors into our formulation. An explicit polygonal 
model
        of the cortical manifold is first constructed as follows: (1) slice
        data in three orthogonal planes of section (needle-shaped voxels)
        are combined with a linear deblurring technique to make a single
        high-resolution 3-D image (cubic voxels), (2) the image is 
recursively
        flood-filled to determine the topology of the gray-white matter 
border,
        and (3) the resulting continuous surface is refined by relaxing it
        against the original 3-D gray-scale image using a deformable 
template
        method, which is also used to computationally flatten the cortex
        for easier viewing. The explicit solution to an error minimization
        formulation of an optimal inverse linear operator (for a particular
        cortical manifold, sensor placement, noise and prior source 
covariance)
        gives rise to a compact expression that is practically computable
        for hundreds of sensors and thousands of sources. The inverse 
solution
        can then be weighted for a particular (averaged) event using the
        sensor covariance for that event. Model studies suggest that we may
        be able to localize multiple cortical sources with spatial 
resolution
        as good as PET with this technique, while retaining a much more fine
        grained picture of activity over time.},
  pdf = {MEG_EEG_source_DaleSereno1993.pdf},
}








Teresa Wong wrote:

> Dear colleagues,
>  
> I would like to hear your views on whether scalp ERPs can reflect 
> activity of the amygdala.
> Is it possible/valid to localize dipole sources (using 128-channel 
> recordings, emotional faces as stimuli) in subcortical brain regions, 
> limbic areas, amygdala, etc?
>  
> Wishing you all a very happy and healthy 2006 with much success in 
> research!
>  
> Teresa
> -- 
> Teresa Ka Wai Wong
> PhD Student
> Department of Psychiatry
> The University of Hong Kong
>  
>
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>
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