NEW YORKChennel King, a nurse from Norwalk, Conn., went Christmas shopping the other day with a new holiday companion: a budget.

Despite a tough economic situation - her husband was laid off almost a year ago - King didn't want to disappoint her five children. So she still went to a mall in suburban New Jersey, but with a limit of $200 per child.

Plenty of Americans are having to hold back this year as the lure of flashy ads, tempting bargains and family expectations clashes with the realities of the economy. Experts in consumer behavior say that situation can strain the brain.

Scientists say we are to some extent wired for shopping. It seems to tap into circuits that originally spurred our ancestors to go out looking for food, says Brian Knutson, an associate professor of psychology and neuroscience at Stanford University.

"We are built to forage, just like rats, just like dogs," Knutson said. So we have brain circuitry that "compels us to go out there ... to get good stuff, even if we don't know what that good stuff is."

Brain scanning in his lab shows deep brain circuitry called the nucleus accumbens goes to work when people are considering products and prices. When brain cells in that area release a chemical called dopamine, people are motivated to take action, he said.

So the very prospect of shopping - maybe brought on by ads and other marketing tools - may arouse that circuitry and put us in a mood to hit the stores, and then to keep on shopping, he said. "You feel good... It's exciting," Knutson said.

Other circuitry reacts to excessively high prices and dampens the enthusiasm to buy, he said. The competing signals - buy and don't-buy - are passed to the front of the brain, in the prefrontal cortex, where a decision about whether to purchase something is apparently made, he said.

But how does that decision get made when money is tight? Knutson said he hasn't studied that question. But he notes that yet another area of the brain, called the cingulate cortex, responds to conflicts like wanting to buy something that costs too much. So maybe it pitches in when a shopper feels restrained by a budget.

King, the recent mall shopper, isn't sure how much she spent last year but it was a lot, with new bedroom sets, a camera for one daughter, a camcorder for one son, and four PlayStations. This year, she turned down the requests of her oldest two for an iPad. But she didn't consider cutting out Christmas totally. And she's mindful to buy the same number of presents for each kid.

"You only live once," King said. "If it's something my kids really want, I try to get it at the lowest possible price."

From what experts recommend about holding down spending, King was smart to set a budget ahead of time, but she probably made her task tougher by going to a mall.

When you're surrounded by attractive goods and crowds of people buying them, "natural human desires can trigger off intense cravings" to buy, says George Loewenstein, a professor of economics and psychology at Carnegie Mellon University. "Not spending when you're tempted to spend is exhausting and miserable," like not eating when you're hungry, he says.

Trying to apply will power "should be your last resort," he said. Much better is to stay away from the mall in the first place, "and it will be much easier to exert self-control."

It might be preferable to shop on the Internet so you're not surrounded by buyers, although the convenience of online shopping holds its own temptations, he said.

If you do go to a mall, commit yourself beforehand to a hard limit on spending, Loewenstein recommends. "Generally, people tend to be a lot more tempted when there is some kind of uncertainty about whether you're going to get whatever it is you're tempted by," he said.

A definite budget removes that uncertainty when a shopper spots something extra, and so it's easier for the brain to say no, he said.

But how to make that budget limit stick? "The last thing you want to do is spend with a card, especially a credit card, or even a debit card," he said. "It doesn't feel like spending."

Much better to count out some cash and put it in an envelope. When the cash is gone, you're done shopping. Even before then, the act of forking out cash introduces "the pain of paying," which can make a shopper more rational and less vulnerable to impulse purchases, he said.

To Kathleen Vohs, an associate marketing professor at the University of Minnesota, Christmas shopping on tight money is "a classic dilemma between Wants and Shoulds," between enjoying something now or holding back for a payoff later. If you don't give in now, "your wallet will be fatter" later, she says.

Her tips for exerting self-control: Shop alone. Carry a list of things you want to buy, so you don't get drained psychologically by having to make a lot of choices in stores. And if you're trying to hold down spending, ease up on other demands for self-control like dieting.

"If you're trying to watch your waist and you're trying to watch your wallet ... it's probably not a good recipe at being successful at both of those," she said.

In fact, willpower to resist overspending can get depleted over hours of shopping as people face temptations, so that self-control and wise decision-making gradually break down, says psychologist Roy F. Baumeister of Florida State University.

When it gets depleted, people will pay more money for the same products and buy more things on impulse that they don't really need, said Baumeister, co-author of the new book, "Willpower: Rediscovering the Greatest Human Strength."

Like Vohs, he recommends trying to limit the number of decisions or demands on self-control you face. And if that's not possible over the course of a shopping day, he said, "try not to make expensive decisions at the end."

But what do you do when you've decided to buy a $1,000 TV, but then you see another model for $1,500 that has more features? If you buy the less expensive one, won't you miss what you passed up for just $500 more?

That's the time to ask yourself, "What else could I do with that $500?" says Michael I. Norton of Harvard Business School. "It really changes your mindset."

If you think about using the money to vacation in Florida or invest in a college fund, "that can help you avoid buying more expensive things," he said.

One more tip to hold down Christmas spending comes from King, the mall shopper.

Her gift list included her niece and goddaughter, but no grown-ups.

"The adults," she said, "they have to wait till their birthdays."

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AP business writer Christina Rexrode reported from Elizabeth, N.J. Follow AP retail coverage at http://www.twitter.com/AP_Retail .

Follow Ritter at http://www.twitter.com/malcolmritter .