Biomedical Engineering Reference
In-Depth Information
maximally in the frontal cortices and greatest towards the midline
(
Fig. 9.1A
)
(8-11)
, and this distribution is also found in animal
models of absence seizures
(12-15)
(
Fig. 9.1B
). Human and
animal studies to date have implicated the cortex and thalamus
in the generation of abnormal network oscillations involved in
SWDs
(16-23)
. However, it has not been definitively determined
whether it is an overall increase or decrease in neuronal activity in
cortical and subcortical circuits that leads to spike-and-wave activ-
ity
(14, 15, 24-26)
. While the electrographic signature and distri-
bution of SWDs have been characterized in previous studies, this
review intends to discuss the question of metabolic activity and
neuroenergetics during SWD. It is hoped that an extensive under-
standing of the neuronal activity changes during SWD might lead
to improved treatment for absence seizures.
3. Neuroimaging
in Generalized
Epilepsy
Although EEG provides high temporal resolution, it is limited
in its spatial sampling and cannot fully describe seizure activity
throughout the brain. Neuroimaging techniques provide more
comprehensive spatial sampling and can look deep into subcor-
tical structures in which EEG recordings are not generally feasi-
ble in humans. The first goal of neuroimaging studies of SWD
is the localization of seizure activity in specific brain regions as
well as the identification of distributed networks during SWD.
Because fMRI signals are only an indirect measure of neuronal
activity, comparable animal models of SWD are necessary to
(1)
relate fMRI signal changes seen during SWD to underly-
ing physiology and
(2)
aid the interpretation of fMRI changes
seen in human SWD. Understanding the brain regions respon-
sible for SWD generation yields numerous therapeutic implica-
tions including improved applications of deep brain stimulation,
more effective medications, and the possibility of targeted gene
therapy. A second goal of SWD fMRI research is to understand
the brain's physiology during abnormal activity of spike-and-wave
discharges. For example, the study of epileptogenesis might be
furthered by identifying those areas which may be more suscep-
tible to chronic activity-dependent changes
(27)
. Finally, a third
goal is to relate fMRI changes throughout the brain to behav-
ioral changes during seizures. Pairing behavioral analysis, includ-
ing studies of impaired consciousness, with identification of the
brain areas that demonstrate changes in fMRI signal will lead to a
greater understanding of functional brain impairment during and
between seizures
(3, 17, 28)
.
