Sleep deprivation (SD) results in a decline in cognitive performance. Our research uses functional imaging to study the neural correlates of this decline with a view to understanding the underlying mechanisms. We are also interested in why some individuals are better able to maintain cognitive performance when sleep deprived better than others.

To date, we have explored imaging and behavioral changes in short term memory, visual attention, inhibition of unwanted responses and risky decision-making following 24 hours of total sleep deprivation.

The first experiments we performed tested verbal working memory. We were initially interested in how performing a more complex task might result in better maintenance of performance than engaging in a simpler task (Chee and Choo, 2004). We found that this is the consequence of greater task related frontal lobe activation. The frontal lobe figures prominently in theoretical accounts of why behavior changes after sleep deprivation. We found how sleep deprivation modulates activation in frontal lobe activation to be strongly task and individual dependent.

Later experiments with short-term memory showed that the extent to which parietal lobe activation declines following sleep deprivation corresponds to increased performance variability. Changes in parietal lobe activation appear to be a promising marker of vulnerability to memory decline.

We have found that it may not be memory storage failure per se but decline in attention and visual processing that may underlie performance drops in short term memory after sleep deprivation (Chee and Chuah, 2007). We are actively pursuing further investigation into this 'sensory failure' hypothesis using different experimental paradigms (Chee et al., 2008).

Our work regarding inhibition showed that most subjects exhibit tonic or sustained decline in activation in some parts of the frontal lobe after sleep deprivation (Chuah et al., 2006). Interestingly, persons who are more likely to lose inhibitory efficiency following sleep deprivation recruit the right inferior frontal region to a greater extent after normal sleep. These persons appear unable to increase activation of this area further following sleep deprivation. This finding further illustrates that there are neural correlates to inter-individual differences in tolerance of sleep deprivation.

Regarding risky decision-making, we found that the nucleus accumbens, an area in the brain that is involved with the anticipation of reward was selectively more active when risky decisions were made under conditions of sleep deprivation. The number of high-risk decisions did not increase with sleep deprivation - but the expectation of being rewarded for making the high risk gamble appears to be elevated. Allied to this finding, we observed an attenuated response to losses in the insula. The insula is a part of the brain that is involved in evaluating the emotional significance of an event. Our findings show how sleep deprivation could pose a double threat to advantageous decision making (Venkatraman et al., 2007).

By discovering functional imaging markers of SD tolerance, we hope to be able to evaluate interventions designed for individuals who are vulnerable to SD. The first example of this line of research concerns the use of the cholinesterase inhibitor donepezil in ameliorating visual attention deficits in the setting of SD (Chuah and Chee, 2008). In this proof-of-concept study, we found that cholinergic augmentation benefits individuals who show performance decline after SD but that persons who don’t decline do not benefit and may actually deteriorate a little. We found fMRI task-related signal change to parallel behavioral changes causing us to be excited about the prospect of using fMRI as a supplementary marker for the evaluation of SD countermeasures.

We also hope that our imaging markers may help inform individuals of their suitability for occupations where repeated and prolonged sleep deprivation come with the job. We will be working with collaborators to identify genetic markers for susceptibility to cognitive decline under conditions of sleep deprivation.

In addition to the published fMRI work, the lab is beginning to run neurophysiological studies using EEG.

The signal-processing group that supports this work is also involved in evaluating some ‘hot’ areas – evaluation of resting state activity and the relationship between task-related deactivation and activation. We are also working on some really cool stuff related to multi-voxel pattern analysis of visual attention data.

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If you are healthy, have generally good sleep habits, and are interested to be a participant in one of our sleep studies, please fill in the questionnaire on this page, and we will be in touch with you if you meet our volunteer requirements.