Last January, a group of UCLA psychologists published research confirming a truth known to anyone who has spent serious time in a casino: When people start thinking about potential losses, most gamble not to lose rather than to win. Using magnetic resonance imaging, the study showed that when subjects were made aware of how much they stood to lose on a wager, neural activity in the parts of the brain that respond well to winning, chocolate, and other good things was depressed. We’re apparently hardwired to be more sensitive to potential loss than to potential gain.

Here you have an explanation for the continued caterwauling over the Yankees’ willingness to include top prospect Phil Hughes in a potential trade for Minnesota Twins ace Johan Santana. (Yankee claims are that such a trade will be completed this week if at all, but as the Alex Rodriguez negotiations proved, such claims are to be taken only so seriously.) Hughes, all agree, has the tools to become a frontline starter, and will make very little money for the next few years. Still, trading a 22-year-old, even one with the potential to be the best homegrown Yankees starter since Whitey Ford, for the best pitcher in baseball makes good sense. Coming out against it may have more to do with brain chemistry than with a dispassionate appraisal of the facts.

Everyone knows that even highly touted young starters are sketchy propositions, but most people probably don’t appreciate just how sketchy they are. From 2000 to 2004, for instance, 29 different pitchers (not counting Jose Contreras, who as an established veteran was not really a prospect) earned a top 20 spot in Baseball America’s annual ranking of the best prospects in the game. These pitchers have collectively had 36 seasons in which they qualified for the ERA title and posted an average park-adjusted ERA, and of those 36 seasons, 21 belong to four pitchers: Roy Oswalt, C.C. Sabathia, A.J. Burnett, and Mark Mulder. Those four, plus Kip Wells and Ben Sheets, account for 59% of the total innings thrown by all 29 pitchers.

There are, of course, other highly valuable properties on this list, such as Josh Beckett and Scott Kazmir, but looking over any list of this sort, it’s striking how highly concentrated the value is. The problem with high-end pitching prospects isn’t just that they have a high attrition rate, it’s that they’re all-or-nothing propositions. They tend to either become stars or contribute almost zero value. It’s only a slight exaggeration to say that right now Hughes’s entire worth is in his one-in-five shot of becoming a true star.

The above-referenced neuroscience suggests that because of the way the brain works, most people will focus on the one rather than the five, but for the Yankees it’s the latter that’s more important. Hughes is a terrific young pitcher — last February I wrote that he had a good chance of being the Yankees’ best starter, and down the stretch he may well have been — but more important than his absolute potential are the odds of his reaching it. No matter how good he was in September they simply aren’t very high, and they’re not what people should focus on. Especially if these people happen to be professional baseball executives who are paid to think things through rationally rather than responding with the lizard-like parts of their brains.

Instead, a potential deal — for Santana or anyone else — should be thought of at least as much in terms of potential gain as of potential loss. One way to frame this is to point out that there have been only 21 individual seasons this decade in which a qualifying American League pitcher has posted an ERA of 3.33 or below. Santana has matched or bested that mark every year he has been a starter, and he’s just 28. Even allowing that he’s in decline (a point I personally wouldn’t concede) he’ll probably pitch for the foreseeable future at a level Hughes will likely never reach.

The difference between the probability that Santana will contend for Cy Young awards for the next several years and the probability that Hughes will even be a consistently effective starter isn’t just an abstract concept. It has a price — to oversimplify, it’s the difference of $100 million or so between the artificially depressed salaries Hughes will earn until he’s eligible for free agency and the salary Santana will earn over that time. There is a very good argument to be made that the Yankees should be unwilling to pay it, especially because they’d be paying a 40% luxury tax on it, but this argument has much less to do with Hughes’s potential than with the inherent dodginess of even truly great pitchers like Santana.

Of course there’s a real chance that Hughes will be the next Roy Oswalt while Santana will blow out his arm next year, but that’s why a trade is a gamble. The point is to stack the odds in your favor consistently, not to eliminate the chance of losing something, and one way for smart baseball teams to do this is to market prospects while they’re at the likely height of their value. As impulse-driven as the Hank Steinbrenner Yankees may seem, in this case at least, they’re behaving very much like a smart baseball team.

tmarchman@nysun.com