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A
Morning PVT
B
Afternoon PVT
Figure 7.4 Time-of-day effects on absolute cerebral blood flow (CBF) activation during
the Psychomotor Vigilance Test (PVT). Twenty healthy adults performed the PVT in the
morning (between 0700- and 0900 h) and a separate group of 15 healthy adults per-
formed the PVT in the afternoon (between 1400- and 1700 h)—both groups did so dur-
ing ASL perfusion f MRI scanning. Brain scans at both times of day showed significant
activation in the sensorimotor, cingulate, and frontoparietal regions. However, thalamic
activation (indicated by the arrows in A) was only observed in the morning scan while
increased activation in the right frontal eye field (indicated by the arrow in B) was
observed in the afternoon scan (Hengyi Rao, unpublished data).
examine daily variations in resting brain functional connectivity and found
that the DMN and sensorimotor network showed highly rhythmic connec-
tivity patterns while the executive control network was most stable across
the day.
255
Almost all published neuroimaging studies to date have focused on acute
total sleep deprivation or time-of-day effects—very few studies have exam-
ined the dynamic effects of chronic partial sleep loss and recovery on brain
function and their interactions with circadian timing. Findings from the few
available ASL and resting-state FC-fMRI studies already provide some
important new insights. However, application of these newmethods to sleep
deprivation and circadian research is still in the early stages and studies are
needed to further elucidate the dynamic effects of both acute and chronic
sleep loss as well as circadian timing on neural activity.
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