Affiliations: Department of Neurology, Yale University School of
Medicine, 333 Cedar Street, New Haven, CT, USA | Department of Neurobiology, Yale University School of
Medicine, 333 Cedar Street, New Haven, CT, USA | Department of Neurosurgery, Yale University School of
Medicine, 333 Cedar Street, New Haven, CT, USA
Note: [] Corresponding author: Hal Blumenfeld, MD, PhD, Yale Depts.
Neurology, Neurobiology, Neurosurgery, 333 Cedar Street, New Haven, CT
06520-8018, USA. Tel.: +1 203 785 4836; Fax: +1 203 737 2538; E-mail:
hal.blumenfeld@yale.edu
Abstract: The default mode network has been hypothesized based on the
observation that specific regions of the brain are consistently activated
during the resting state and deactivated during engagement with task. The
primary nodes of this network, which typically include the precuneus/posterior
cingulate, the medial frontal and lateral parietal cortices, are thought to be
involved in introspective and social cognitive functions. Interestingly, this
same network has been shown to be selectively impaired during epileptic
seizures associated with loss of consciousness. Using a wide range of
neuroimaging and electrophysiological modalities, decreased activity in the
default mode network has been confirmed during complex partial, generalized
tonic-clonic, and absence seizures. In this review we will discuss these three
seizure types and will focus on possible mechanisms by which decreased default
mode network activity occurs. Although the specific mechanisms of onset and
propagation differ considerably across these seizure types, we propose that the
resulting loss of consciousness in all three types of seizures is due to active
inhibition of subcortical arousal systems that normally maintain default mode
network activity in the awake state. Further, we suggest that these findings
support a general "network inhibition hypothesis", by which active inhibition
of arousal systems by seizures in certain cortical regions leads to cortical
deactivation in other cortical areas. This may represent a push-pull mechanism
similar to that seen operating between cortical networks under normal
conditions.
