Learning from the Unexpected
As any slot-machine operator can tell you, what keeps gamblers hooked to the lever is the random and unpredictable nature of jackpot payouts. It’s a classic tenet of operant conditioning: unexpected rewards have an unusually powerful effect on learning and behavior. For the first time, a research team led by Penn neurosurgery postdoctoral fellow Kareem Zaghloul has recorded the neural activity underlying this process in humans. They published their findings in the March 13 issue of Science.
The scientists asked people with Parkinson’s disease to play a computer card game involving a choice between two decks, one of which carried a higher probability of yielding a virtual financial reward. Microelectrodes implanted in a part of the brain called the substantia nigra (SN) recorded significantly higher rates of firing in dopaminergic neurons after unexpected gains than after unexpected losses, while no such differences were observed after expected gains and losses. “Our findings suggest that neurons in the human SN play a central role in reward-based learning, modulating learning based on the discrepancy between the expected and the realized outcome,” the authors conclude. This sheds new light on a part of the brain that has been suspected of playing a role in addiction and various disorders involving reward-seeking behavior.
The Bachelor Blues
An experiment revealed that the reproductive life of a male mouse can be extended by as much as 20 percent by means of a simple mechanism: just sharing a home with a female. Researchers led by Ralph Brinster V’60 Gr’64, the Richard King Mellon Professor of Reproductive Physiology, found that male mice that live on their own lose their fertility at around 26 months of age, compared with 32 months for those placed in co-ed housing. Their finding was published in January in Biology of Reproduction.
The underlying mechanism remains unclear, although it appears that defects in the sperm-production process are at play.
“If it turns out that this reproductive effect is mimicked in other species,” Brinster said, “a 20 percent increase in male fertility could mean an extension of the male reproductive life-span of years” for some livestock animals.
Swallowing the Holiday-Suicide Myth
If you’ve read that suicides peak during the winter holiday season in the United States, you’re not alone. The popular press trots out that supposed fact every time the decorations go up. The problem is, it’s not true. There are actually fewer suicides in December than any other month, according to national health statistics.
The Annenberg Public Policy Center first debunked this myth in 2000, but a recent APPC analysis of the latest crop of stories showed that half of them got it wrong. That represented quite a relapse; the year before, only 10 percent missed the mark.
“Perpetuating the myth not only misinforms the public,” said APPC director Kathleen Hall Jamieson. “It also misses an opportunity to educate the public about the most important risk factors for suicide— namely, mental disorders.”