Study designed to test sleep deprivation network, by influencing the expression of key brain areas in the network
In a previous study , the investigators identified a sleep deprivation network of brain areas that was active during the performance of a working memory task. Expression of this network was reduced following sleep deprivation. They also found a relationship between reduced expression of this network following sleep deprivation and poorer performance on the working memory task.
In the study, 15 young, healthy subjects underwent sleep deprivation for 48 hours. Working memory was tested using a letter recognition test, known as the delayed match to sample (DMS) task, in which subjects have to recall as quickly as possible whether a letter was included in a set of letters they had just seen. Participants performed this task during fMRI sessions both before sleep deprivation and at the conclusion of the sleep deprivation period.
The researchers used repetitive transcranial magnetic stimulation (rTMS) to test whether stimulation of three brain regions in the previously identified network following the sleep deprivation period, could improve performance on the working memory task. rTMS administers a rapid sequence of magnetic pulses to a specific brain area.
Results showed that stimulation at a site over left lateral occipital cortex, a prominent part of the brain network identified with fMRI, resulted in a reduction of sleep-induced slower reaction time without a corresponding decrease in accuracy. This improvement in performance was most marked in those individuals who showed the greatest reduction in the expression of the brain network following sleep deprivation.
“In addition to expanding our understanding of cognitive decline in the elderly, these findings may also have implications for new ways to treat sleep deprivation, a pervasive problem for soldiers, truck drivers and night-shift workers, which can result in impairment on the job and accidents,” said Dr. Stern.
‘Cognitive reserve’ varies among individuals
Elderly persons show a broad range of individual differences in the degree to which they experience cognitive deficits as they age. One hypothesis to explain these differences was first formulated by Dr. Stern in 2002 and has since been adopted by neuroscientists worldwide, and is known as cognitive reserve. The theory of cognitive reserve suggests that some individuals are better able to cope with age-related or other neuropathology because they can call upon more neural resources.
These present findings are consisted with the concept of cognitive reserve because some participants suffered larger deficits in working memory performance due to sleep deprivation, while others were much less affected. These susceptibility differences were related to differential expression of a brain network.
This suggests that the activity of the sleep deprivation network exhibited properties of neural reserve, where a greater capacity or efficiency in the network allowed some individuals to maintain performance in the face of sleep deprivation. Moreover, these results suggest that rTMS was able to somehow enhance the network activity in those who were not able to maintain performance, artificially facilitating neural reserve.
Source: Columbia University Medical Center