Читать книгу The New IQ: Use Your Working Memory to Think Stronger, Smarter, Faster - Tracy Alloway - Страница 64

Is your working memory also working against you when you want to lose weight but can’t seem to step away from the dessert tray? Do you just lack willpower? Or is something else preventing you from getting control over your eating? Consider Michael, a man from New York who weighed twelve hundred pounds. Partly encouraged by an obese mother, he liked to start the day with four bowls of cereal, toast, waffles, cake, and a quart of soda, and end it with a pizza. Michael tried diet after diet, but he was unable to control his urges.

New science suggests that some of us may in fact be addicted to fat. Considering that two-thirds of U.S. adults are overweight or obese, it is clear that a lot of us are eating more than our fair share of fatty foods, and it is having a devastating impact on our working memory. A 2007 study in the journal Appetite found that obese children perform worse on tests involving working memory compared to their non-obese peers. When you hit middle age, it doesn’t get any better. In 2010, researchers from the University of Texas at Austin found that when obese individuals performed a working memory task, there was less activation in a brain area associated with working memory compared to normal-weight people or those who were just somewhat overweight.

In 2003, scientists at Boston University found that senior citizens who were obese and had hypertension had poorer working memory skills. Other research appearing in Current Alzheimer’s Research in 2007 shows that being obese in midlife is linked to cognitive disease later in life. People who were obese in middle age were five times more likely to be diagnosed with vascular dementia and three times more likely to develop Alzheimer’s. And don’t think you’re off the hook if you’re just a little pudgy rather than outright obese. In this same study, people who were overweight were two times more likely to develop Alzheimer’s or vascular dementia in their not-so-golden years. These studies with humans offer a useful first step in understanding the link between overeating and working memory. More recent research has benefited from using rats in order to more rigorously control experimental conditions—like altering brain cells or introducing electrical shocks—allowing scientists to learn how overeating can be addictive and ultimately impair working memory.

In 2010, neuroscientists Paul Johnson and Paul Kenny of the Scripps Research Institute in Florida set out to understand how fatty foods can act like a drug in the brain to send the reward system spiraling out of control. They took three groups of rats and fed them a variety of diets to see how fatty foods affected their brain and weight. Group 1—we’ll call them the smorgasbord rats—enjoyed nearly unlimited access to high-fat foods, kind of like going to an all-you-can-eat buffet—including some human favorites like bacon, sausage, chocolate, and cheesecake. Group 2—we’ll call them the restrained rats—had access to the same fatty foods but only for a short period once a day. Group 3, a control group—we’ll call them the healthy rats—had access to only healthy rat food. Can you guess what happened? It’s no big surprise that the smorgasbord rats ended up consuming twice as many calories as the healthy rats and quickly grew obese.

The researchers then conditioned the rats: every time a light went on, they would receive a mild electrical shock. The next time the groups went to feed, the researchers turned on the light and waited to see what would happen. The restrained rats and the healthy rats refused to eat when the light was switched on, but the smorgasbord rats went straight for their food. They had become so addicted to the fatty fare that the threat of a mild electrical shock couldn’t deter them from scarfing down every bite.

Johnson and Kenny also wanted to explore more fully the role of dopamine in food addiction. As we’ve said, a person who becomes addicted to a substance tends to need more and more of it to get that same surge of dopamine. That’s because an addicted brain has fewer dopamine receptors to receive the dopamine signals.

Johnson and Kenny wanted to find out what the smorgasbord rats would do if they had fewer dopamine receptors, so they inserted a virus in their brain to attack the receptors. The researchers expected that the rats would gradually adjust and eat less of the fatty food because it didn’t provide the same dopamine high. Imagine their surprise when they found that the rats resorted to eating even more to try to achieve the same high.

So if you’ve ever wondered why it takes three candy bars to get the same satisfaction when it used to take only one, now you know that your brain might be compensating for the declining dopamine receptors. This also helps explain why some of us continue to gorge on fattening foods even though we hate the fact that we can barely zip up our pants, have type 2 diabetes, and are saddled with high blood pressure.

The research on diet and working memory also suggests that overindulgence in fatty foods directly assaults your working memory. Andrew Murray and colleagues at the University of Oxford took two groups of rats. Both were fed a healthy diet for up to two months and were given a working memory test for rats known as a radial maze task. This commonly used task for measuring working memory in rats uses an elevated platform with eight arms that extend from the maze in the center. The rats learn which of the arms have a food reward hidden out of sight at the end of the arm. A working memory error is counted when the rat goes to an arm with no food even though the animal looked there previously. This is considered a working memory task because the rat has to navigate the maze and at the same time hold in mind where it has already been. The researchers noted the scores of the groups.

After this test, they fed one group a high-fat diet for nine days and retested the two groups. The rats on the healthy diet blasted through the maze, and though they weren’t perfect, they scored slightly higher than they did the first time. The rats on the high-fat diet took a lot longer to complete the maze than they did the first time and made more mistakes. The high-fat diet apparently diminished their working memory ability.

Other theories about specific foods that turn the brain reward system against us abound. In 2009, David Kessler suggested that it’s foods that combine salt, sugar, and fat that do a number on the brain’s reward system and lead to overconsumption and obesity. Sugar has also been implicated on its own, including high-fructose corn syrup, maltose, dextrose, and dozens of other sugar sources found in our food supply. As scientists attempt to pinpoint a single food, category of food, or combination of foods that trip up our reward system, it seems that it’s when we overindulge in these foods that it becomes a problem. After all, it is important to remember that the human body needs fat for a healthy brain, needs glucose to think clearly, and needs salt. But when we overindulge, our working memory suffers.