Circadian Rhythms, Sleep Deprivation, and Human Performance - Progress in Molecular Biology and Translational Science - page 176

technique—cannoninvasivelymeasure absolute cerebral blood flow(CBF) that
is tightly coupled to regional brain function, 240,241 providing a method for
imaging variations of brain function at different time of day or circadian phases
or after sleep loss. ASLhas been increasingly used to assess waking brain function
at task-free resting states as well as during different cognitive tasks. 242,243
We successfully used ASL to quantify CBF changes after prolonged cog-
nitive workload without sleep loss. 244 Currently, only one published study
has used ASL and measured resting CBF changes after one night of sleep
restriction. 245 This study reported significantly reduced frontoparietal
CBF following sleep loss, but only in participants with significant signs
of drowsiness, while nondrowsy participants maintained CBF in the
frontoparietal regions and increased CBF in basal forebrain and cingulate
regions. These findings also suggest a potential neurobiological mechanism
to compensate for drowsiness after sleep loss. Ongoing studies in our group
as well as others are using ASL to quantify regional neural activity changes
associated with time-of-day variation and sleep deprivation. 246 Our prelim-
inary data from scans during PVT performance in the morning and after-
noon in two independent groups also showed significant time-of-day
effects. Both morning and afternoon scans showed similar sensorimotor, cin-
gulate, and frontoparietal activation while subjects performed the PVT.
However, thalamic activation was observed only in the morning PVT scan,
while increased activation in the right frontal eye field was observed in the
afternoon PVT scan ( Fig. 7.4 ) .
Another emerging imaging method for studying sleep deprivation and
time-of-day or circadian phase effects on brain activity is resting-state func-
tional connectivity fMRI (FC-fMRI), which usually uses low frequency
fluctuations of resting-state BOLD signal to examine intrinsic and spontane-
ous neural activity in the absence of external stimuli or tasks. 247,248 Con-
verging evidence from resting-state fMRI studies has indicated an
organized mode of resting brain function and identified a number of
brain networks associated with different domains of neurocognitive func-
tioning. 249-252 Two recent studies have used FC-fMRI to investigate the
effect of one night of either total or partial sleep deprivation on functional
connectivity. 253,254 Both studies found that sleep deprivation reduced
resting functional connectivity within the default mode network (DMN)
and between DMN and its anticorrelated network, suggesting that reduced
brain functional connectivity may be a precursor to behavioral impairments
from sleep loss.

In addition, one recent study used FC-fMRI to