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46.1 Specific areas within the five lobes of the cerebral cortex have sensory, motor, and associative functions.

46.3 Sleep deprivation impairs cognitive functions.

46.3 Language functions are lateralized (typically within the left cerebral hemisphere). Language ability involves parts of the occipital, parietal, temporal, and frontal lobes.

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.

Accuracy (%) RW SD24 SD35 Reaction
time (ms)
RW SD24 SD35
LTR 95.2 86.5* 85.0* LTR 745 792* 769
PLUS 95.0 86.6* 84.3* PLUS 698 747* 746*

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Questions

Question 1

Based on the data in the table, justify the conclusion that sleep deprivation impairs working memory.

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

One interpretation of the reaction-time data in the table is that they reflect decreased alertness after sleep deprivation. What information would lead to this conclusion? What is another way to explain the results?

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

Based on the information in the text, explain why the areas of the cerebral cortex shown in the graph were more affected by sleep deprivation than most other areas of the cerebral cortex examined in this study.

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

After looking at the MRI data, the researchers concluded that sleep deprivation has a stronger effect on the parietal lobe than on the frontal lobe. How do the data support that conclusion? What statistical comparison would you use to test this conclusion?

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.

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