Sleep deprivation can make it hard to concentrate. A possible reason is that neurons in different regions of the brain seem to go 'off line,' or shut off for brief periods, during forced periods of wakefulness, according to a study of rats published in Nature. U.S. and Italian researchers kept laboratory rats awake for four hours past their normal sleep time by stimulating them with new objects. EEG (electroencephalogram) readings, which test the brain's electrical activity, were typical of an awake state and the rats moved about freely with their eyes open. However, electrodes implanted in the rat brains showed that some neurons went off line briefly in seemingly wide-awake animals while other neurons remained on. Neuronal off periods increased with prolonged sleep deprivation, impairing the rats' performance in the routine task of reaching for a sugar pellet. Researchers said these off periods during wakefulness aren't well understood but they may be a means of conserving energy or part of a restorative process.
Caveat: It's not clear if the periods of neuronal off-time reflect the capacity of neurons to exist in two states, a phenomenon known as bistability, researchers said.
Stocks and hearts: Stock-market investors may be at increased risk of heart attack and sudden death during periods of extreme market volatility, according to research carried out in Shanghai, the financial capital of China, and published in the European Heart Journal. The study, carried out during a period of sharp gains and declines in stock prices from 2006 to 2008, found that each 1% change in the stock index, either up or down, resulted in a nearly 2% increase in cardiac deaths; on a points basis, each 100-point change in the stock index, either up or down, corresponded with more than a 5% increase in heart-attack deaths. The findings support a 2010 U.S. study, which found that heart-attack deaths increased when stock-market values decreased. In the latest study, researchers said there were 22,272 heart-attack deaths, or about 20.3 per day, during the period studied. Half the deaths occurred out of hospital. The study noted that many Chinese investors were inexperienced retirees with unrealistic expectations for stocks.
Caveat: The researchers did not have access to information about possible pre-existing cardiovascular diseases in the investors. The results may not apply to other areas of the world, as the subjects were a unique, susceptible group of individuals. |