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Original Paper: Chee, M. W. L., L. Y. M. Chuah, V. Venkatraman, W. Y. Chan, P. Philip and D. F. Dinges. 2006. Functional imaging of working memory following normal sleep and after 24 and 35 h of sleep deprivation: Correlations of fronto-parietal activation with performance. NeuroImage 31: 419−428.

Insufficient sleep has negative consequences. There are the physiological ones: lack of energy, difficulty staying awake, and even high blood pressure, diabetes, and stroke. And what about cognitive abilities—functions such as memory and alertness? Looking for answers, researchers ran tests on three groups of subjects. In the first group, subjects were rested and wakeful. This “RW” group was compared with subjects who were sleep-deprived for 24 hours (“SD24”) and subjects who were sleep-deprived for 35 hours (“SD35”). The researchers looked at both alertness and working memory (the ability to hold new information in memory for a short time to enable cognitive processing). They also performed brain scans, using magnetic resonance imaging (MRI), to see what specific areas of the brain were affected by sleep deprivation.

In one test (referred to as the LTR test), subjects looked at a picture of four capital letters for 0.5 seconds. Three seconds later they were shown a lowercase letter for 1.5 seconds and were to press a button if the lowercase letter matched one of the capital letters they had just seen.

The second test (referred to as the PLUS test) required more cognitive processing than the LTR test. In the PLUS test, subjects looked at a picture of two capital letters for 0.5 seconds. Three seconds later they were shown a lowercase letter for 1.5 seconds and were to press a button if this was the next letter, in alphabetical sequence, after either of the two capital letters.

The effect of sleep deprivation on working memory was measured by the accuracy of responses of sleep-deprived (SD) subjects compared with rested and wakeful (RW) subjects. The alertness of the SD and RW subjects was measured by their reaction times in milliseconds. The results are shown in the table. Asterisks (*) indicate significant differences between RW and SD subjects.

Using MRI, the researchers measured activation of different brain regions during the testing. Two areas with the most significant differences between RW and SD subjects are shown in the graph. Plus signs (+) indicate significant differences between RW and SD24 subjects; hashtags (#) indicate significant differences between RW and SD35 subjects.

Questions

Question 1

The subjects who were well rested gave correct answers to working-memory tests at least 95 percent of the time. Sleep-deprived subjects were almost 10 percent more likely to give incorrect answers.

Question 2

Compared with well-rested subjects, sleep-deprived subjects took approximately 50 milliseconds longer to answer the questions, which could reflect decreased alertness. The results could also be due to an effect of sleep deprivation on cognitive processing time.

Question 3

The left side of the cerebral cortex is responsible for processing and understanding language. Since the tests involved letter recognition and sequencing, this is likely to be the area most activated by the tests.

Question 4

Sleep deprivation caused a 20-30 percent decrease in parietal lobe activity but only a 10-15 percent decline in prefrontal lobe activity. Testing this conclusion would require a statistical evaluation of the differences between activities in the two brain areas as a function of the sleep-deprivation treatment.