A recent article by Press Democrat reporter Kerry Benefield ("Sonoma County students, educators debate later start to high school days," Sept. 5) discussed the effect fatigue and lack of sleep can have on a student's learning potential.

For example, according to brain scientists, there are certain periods during the school day when students learn more efficiently. A student's circadian rhythms — biological clocks that regulate periods of sleepiness and wakefulness — regulate when a student has the highest ability to focus and absorb new material.

Interestingly, cognitive rhythms are about the same for preadolescents and adults, but for adolescents, a group most susceptible to disrupted sleep patterns, this cognitive rhythm occurs one hour later.

Most teachers are acutely aware that 8 a.m. to noon is a high learning period, when students' circadian rhythms are considered best for learning. However, the weakest time for learning potential is from noon to 4 p.m. From 4 p.m. and later, student circadian rhythms regroup and move back to high points of learning potential.

Unfortunately, there is a Catch-22 to all of this, and that has to do with rapid eye movement, or REM, sleep. Students should be allowed to experience six REM periods over the course of nine hours of sleep. Therefore, the adolescent would have to go to bed at 10 p.m. and get up at 7 a.m. to satisfy the need for six REM cycles.

The selling point is that with each REM cycle, we have greater capacity for memory consolidation. In short, what your student learned during the day has a greater chance of being encoded or stored into long-term memory during REM sleep cycles.

Moreover, memory consolidation occurs more easily when the brain is not preoccupied with external stimuli, which occurs during REM sleep and which also supports your student's circadian rhythms. This may explain why people who review important information before going to sleep are likely to remember that information the next day on a test.

Our major dilemma? We cannot expect students to simply retire to bed early. According to medical researchers, the adolescents' late sleep cycles are part of the maturation of the endocrine system. From the onset of puberty until the late teen years, the brain chemical melatonin, which is responsible for sleepiness, is secreted from about 11 p.m. until around 8 a.m., nine hours later.

This secretion is based on human circadian rhythms and is fixed. In other words, typical students are not able to fall asleep much before 11 p.m., and their brains will remain in sleep mode until about 8 a.m., regardless of what time they go to bed.

The Catch-22 is that many high school classes with early start times will cause students to rise earlier to get to school.

Data from a research study at a major metropolitan public school showed that there was a significant reduction in school dropout rates, less depression and less drug use, accompanied by higher grades, when students' REM sleep and circadian rhythms were addressed.

For starters, we need to look more closely at academic classes that occur during the peak and down periods. The second suggestion is that schools, especially high schools, should start later to support both circadian rhythms and REM sleep patterns as demonstrated by scientific research studies.