**6. Conclusion**

34 Infrared Spectroscopy – Life and Biomedical Sciences

Fig. 8. Significant positive correlation between changes in oxy-Hb concentration and

Fig. 9. Correlation between changes in oxy-Hb concentration and alertness on the 2-back

Fig. 10. Correlation between changes in oxy-Hb concentration and alertness on the 2- and 0-

alertness for the difference between the 2- and 0-back tasks

task (left panel) and 0-back task (right panel)

back tasks for channel 10

When the ROI is compatible with the strengths of NIRS, the technique is valuable for investigating human frontal functioning associated with deteriorated cognition caused by sleep loss. Indeed, our studies demonstrated that certain functional differences in the bilateral PFC under sleep loss conditions correspond to certain cognitive tasks.

We can sum up by saying the PFC mediates various cognitive functions, from basic functions such as simple response to stimulus and time perception to higher functions such as working memory including executive functions, to orchestrate perception, memory,

Effects of Sleep Debt on Cognitive Performance and Prefrontal Activity in Humans 37

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thought, and action in accordance with a given purpose (Halford et al., 2010). The findings discussed here clearly suggest a novel function for the PFC, that of controlling sleepiness and compensating brain function deteriorated by sleep loss.

NIRS is a developing technique and it is expected that its applications will increase to cover other cerebral regions in future and that further noise reductions will improve the technique further: it will undoubtedly provide invaluable information about human cognition and its neural substrates.
