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Anisotropy; EEG/MEG source reconstruction; Finite element method; Local conductivity changes; Return currents; Thalamus; Visualization
Abstract:
nverse
methods
are
used
to
reconstruct
current
sources
in
the
human
brain
by
means
of
Electroencephalogra-
phy
(EEG)
and
Magnetoencephalography
(MEG)
measure-
ments
of
event
related
fields
or
epileptic
seizures.
There
exists
a
persistent
uncertainty
regarding
the
influence
of
anisotropy
of
the
white
matter
compartment
on
neural
source
reconstruc-
tion.
In
this
paper,
we
study
the
sensitivity
to
anisotropy
of
the
EEG/MEG
forward
problem
for
a
thalamic
source
in
a
high
resolution
finite
element
volume
conductor.
The
influence
of
anisotropy
on
computed
fields
will
be
presented
by
both
high
resolution
visualization
of
fields
and
return
current
flow
and
topography
and
magnitude
error
measures.
We
pay
particular
attention
to
the
influence
of
local
conductivity
changes
in
the
neighborhood
of
the
source.
The
combination
of
simulation
and
visualization
provides
deep
insight
into
the
effect
of
white
matter conductivity anisotropy.
We
found
that
for
both
EEG
and
MEG
formulations,
the
local
presence
of
electrical
anisotropy
in
the
tissue
surroun-
ding
the
source
substantially
compromised
the
forward
field
computation,
and
correspondingly,
the
inverse
source
recons-
truction.
The
degree
of
error
resulting
from
the
uncompen-
sated
presence
of
tissue
anisotropy
depended
strongly
on
the
proximity
of
the
anisotropy
to
the
source;
remote
anisotropy
had
a
much
weaker
influence
than
anisotropic
tissue
that
included the source.
