[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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