Circadian Rhythms, Sleep Deprivation, and Human Performance - Progress in Molecular Biology and Translational Science - page 174

utility of PET in imaging human brain metabolism variations associated with
sleep deprivation and time-of-day effects is limited.
The vast majority of sleep deprivation and time-of-day or circadian neu-
roimaging studies are based on the blood oxygenation level-dependent
(BOLD) fMRI. Compared with PET, BOLD fMRI is noninvasive, more
cost effective, and easier to apply, thus making it the most widely used imag-
ing method for localizing regional brain function. BOLD studies typically
compare fMRI signals during a specific cognitive task with those during
a control or baseline condition to obtain task-related brain activation.
A large number of BOLD studies have investigated the effects of acute total
or partial sleep deprivation on brain activation during performance on
a broad range of neurocognitive tasks, including arithmetic calculation, 195
attention, 196-208 decision making, 209-211 emotional processing, 212 episodic
memory, 213-215 inhibition control, 216 logical reasoning, 217 spatial
navigation, 218 verbal learning, 219,220 visuomotor adaptation memory, 221
and working memory tasks. 222-230 Many BOLD fMRI studies have found
changes in neural activity after sleep deprivation. For example, a reproduc-
ibility study showed that brain activation patterns were highly correlated
across test-retest sessions and the magnitude of decreased activation in pari-
etal regions was preserved and reproducibly correlated with behavioral
decline after acute total sleep deprivation. 228 Reduced frontoparietal activa-
tion was found during lapses on a visual, selective attention task in addition
to decreased overall activation after total sleep deprivation. 199 However,
robust interindividual differences in brain responses to sleep loss have also
been reported. Individuals cognitively vulnerable to sleep deprivation
showed reduced frontoparietal activation, while resilient individuals showed
increased parietal activation associated with lapses of attention during total
sleep deprivation 201 suggesting a potential neurobiological compensatory
mechanism in some individuals.
Far fewer neuroimaging studies have been conducted to examine either
time-of-day or circadian phase effects on brain activation. One study used
functional near-infrared spectroscopy to examine circadian variability of
the hemodynamic response in visual cortex throughout the day from
0800-1800 h, reporting no significant time-of-day influences on visual acti-
vation. 231 However, BOLD fMRI studies have shown significant time-of--
day effects on brain activation when subjects performed various
neurocognitive tasks. For example, Gorfine and Zisapel 232 found that left
hippocampal activation was reduced during an autobiographic memory task