Sensory understanding advances by a whisker [pg. 7]

February 12, 2006 02:14
4 minute read.

Studying how rats use their whiskers may seem a bit esoteric. But neurobiologists at the Weizmann Institute of Science in Rehovot have focused on this topic to find out whether there is such a thing as a universal neural code, in which the complexity of sense and experience can be reduced to a few simple rules. Prof. Ehud Ahissar, who with his colleagues have been watching to see how rats use whiskers to sense their environment, says the answer might be no. They have found that the seemingly simple act of feeling out a 3-D object requires three different types of code. Rats' whiskers are highly developed sense organs. To get a fix on their surroundings, rats whisk their whiskers back and forth as they move. Researchers had previously shown that such "whisking" is crucial, but how does a rat's brain perceive a three-dimensional object this way? Sensing begins in the neurons at the whiskers' bases, which then fire signals off to the brain. The scientists, Marcin Szwed, Knarik Bagdasarian and Ahissar, found that in perceiving each of the three dimensions in the rat's surroundings - the horizontal, the vertical, and the radial (distance from the whisker base) - the neurons encode information in completely different forms. To sense the horizontal, for instance, neurons fire with exact temporal precision, and the timing of these signals relative to the whisking motion identifies the horizontal placement of an object. The radial, on the other hand, is encoded in quantity, specifically the number of times the neurons fire. The closer an object is to a rat's snout, the higher the number of neuron-signaling spikes the team recorded. Height seems to be sensed through spacing: Since whisking only takes place in the horizontal plane, the researchers concluded that information about the vertical dimensions of an object is mapped out in the vertical placement of the whiskers, which are arranged grid-like on either side of the snout. In addition to finding different codes for each dimension, the researchers noted that the nerve cells at the base of the whiskers seemed to be specialized for the different kinds of encoding. Now the team plan to continue following the whiskers' signals to find out how the brain melds the three signals into one percept. NO PAIN, NO GAIN Confirming what many have long suspected, scientists have found that male monkeys of two different species gain weight when their mates are pregnant. The 10% gain in male girth occurs in common marmosets and cotton-top tamarins - both squirrel-sized primates known for their monogamous lifestyles and good parenting. Since fathers in these species are heavily involved in infant care, they may be stocking up during pregnancy in preparation for the rigors of fatherhood. University of Wisconsin-Madison's National Primate Research Center endocrinologist Dr. Toni Ziegler and colleagues reported their findings in a recent issue of Biology Letters. The knowledge that expecting primate fathers also experience biological changes can help scientists understand what governs human fathering behavior, Ziegler adds. "We're interested in what motivates dads to be good parents, because there are so many men who just aren't good fathers. This work could help to tease apart what makes a good father." In the past few decades, scientists have noted weight gain and other symptoms of pregnancy in men, but the phenomenon has never been systematically studied. Known as the "couvades effect" - from the French word meaning "to incubate or hatch" - researchers have generally explained sympathetic symptoms in men as entirely psychosomatic events. But the UW-Madison work helps prove that this phenomena is actually real, with a possible evolutionary purpose. "The males somehow cue in to the cascade of hormonal changes going on in their pregnant mates," says Ziegler. That cue triggers changes in their own reproductive hormones. Rising levels of lactation-inducing prolactin most likely cause the weight gain in expecting males. TIME OFF IS NOT TIME OUT This news item will not surprise any busy woman: While more free time sounds like a good thing, new research suggests it is a better deal for males. A study by sociologists at Ohio State University found that men who have more free time feel less rushed than men with less leisure time. But even when women have more time free from paid work and household tasks, they don't feel less rushed. The results, published in the February issue of the Journal of Marriage and Family, suggest that women - particularly mothers - feel the pressures of childcare and housework even when they have time for relaxation, says study co-author Prof. Liana Sayer. "The meaning of free time for men's and women's lives are quite different; especially for wives and mothers, it appears free time is still combined with other activities or responsibilities." The study found that men who were married with children didn't feel more rushed in their daily lives than single, childless men. But the odds of feeling sometimes or always rushed were 2.2 times higher for married women with children than it was for single, childless women. The researchers compared data in two US national surveys conducted among a total of some 2,000 people in 1975-76 and 1998-99. In both surveys, respondents filled out a diary that showed how they spent a specific 24-hour period. Free time was measured as time not spent at paid work, household chores, child care or self care such as eating, grooming and sleeping. Participants were also asked how often they felt rushed during a typical day. The results showed that time pressures increased for women between 1975 and 1998, especially in comparison to men. The fact that women were more likely than men to feel rushed - and were not helped by having more free time - may be related to how men and women view household responsibilities and child care, Sayer said. While this study didn't delve into why women feel more rushed, Sayer said other research suggests they still feel more responsible for taking care of children and housework, even if men are pitching in more than they used to.

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