Brain Scans Helps Scientists "Read" Minds

Of the super powers one might like to have, mind reading would likely land near the top of the list for many people. Now two papers published this week by Nature Neuroscience show how scientists are inching toward this goal. Magnetic resonance imaging (MRI) scans of people's brains, researchers report, can reveal what types of images they have recently seen. Yukiyasu Kamitani of ATR Computational Neuroscience Laboratories in Kyoto, Japan, and Frank Tong of Princeton University showed subjects one of eight visual stimuli--images with stripes aligned in various orientations. They determined that the MRI data collected while the volunteers were gazing at the images showed slight differences depending on what picture they viewed. The scientists wrote a computer program that recognized the patterns and found that they could successfully predict what images subjects saw. What is more, when a volunteer was shown two sets of stripes simultaneously--but told to pay attention to just one--the team could tell which set the subject was concentrating on.

In the second experiment, John-Dylan Haynes and Geraint Rees of University College London showed volunteers two images in quick succession, with the first flashing so quickly that the subjects couldn't clearly identify it. But by analyzing their brain activity, the scientists successfully identified which image had been shown, even when the subjects themselves didn't remember seeing it. Together, the results elucidate how the brain reacts to stimuli, even when they are "invisible." If scientists could gain a true understanding of the neural basis of subjective experience, Kamitani and Tong write, it might one day "allow for reliable prediction of a person's mental state based solely on measurements of his or her brain state." --Sarah Graham

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Too Cold for Comfort

Dark energy chills our galactic neighborhood

By George Musser

Image: USED WITH PERMISSION FROM A. KLYPIN, Y. HOFFMAN ET AL. IN ASTROPHYSICAL JOURNAL, VOL. 596, PAGES 19-33; OCTOBER 10, © 2003 AAS SIMULATED MILKY WAY AND ITS NEIGHBORS are moving (arrows) toward the Virgo Cluster of galaxies. But they are hardly moving relative to one another--maybe because of dark energy or gravitational tides. When you first meet dark energy, it seems so charming. An alluring stranger, outsider to the Standard Model of particle physics, it entered astronomers' lives a decade ago and won their hearts by fixing all kinds of problems, such as discrepancies in the age of the universe and the cosmic census of matter. Cosmic expansion has got its groove back: once thought to be winding down, it is actually speeding up. But astronomers have come to realize that dark energy has a dark side. The cold grip of its repulsive gravity is strangling the formation of large cosmic structures. And now observers see it prowling the neighborhood of our own Milky Way. "You don't need to go so far to find dark energy," says Andrea Macciò of the University of Zurich. "Dark energy is also around us." Up until recently, those seeking the exotica of the universe--dark matter as well as dark energy--focused on the very largest scales (galaxy clusters and up) and on comparatively small ones (a single galaxy). But in between is a poorly studied cosmic mesoscale. The Milky Way is part of the Local Group of galaxies, which in turn is part of the Local Volume, about 30 million light-years in radius. We and the rest of our gaggle are flocking en masse at 600 kilometers per second, lured by the Virgo Cluster of galaxies and other outside masses. Tracking relative motions within the volume, though, is tough; it requires distance and velocity measurements of high precision. Early efforts by Allan R. Sandage of the Carnegie Observatories in Pasadena, Calif., and others in the 1970s, confirmed in recent years, hinted that stuff is moving abnormally slowly--on average, somewhere around 75 kilometers per second. Simulations predict that galaxies, pulled together by gravity, should buzz around at closer to 500 kilometers per second. By analogy with a gas of slow-moving molecules, the Local Volume is "cold."

Another way to think of the problem is in terms of cosmic expansion. Theory predicts that you'd have to go out hundreds of millions of light-years, where matter is spread randomly rather than finely structured, before the overall expansion should outgun localized motions. Yet in the Local Volume, you have to go out only about five million light-years.

One explanation, championed by Igor Karachentsev of the Russian Academy of Sciences, is that galaxies and their individual cocoons of dark matter swim in a sea of dark matter. The sea would mute the density contrasts and hence the gravitational forces that drive galactic motions. The only trouble is that matter, whether dark or visible, should not spread out into a sea. It should clod. So others have looked to dark energy. Its gravitational repulsion would offset galaxies' gravitational attraction, thereby deadening their motion. In and near the Milky Way, attraction wins, but beyond a certain distance, repulsion does. As Arthur Chernin of Moscow University and his colleagues calculated in 2000, this distance is five million light-years--exactly where galactic motions deviate from standard predictions. The initial calculations actually only halved the galactic velocities, which is not enough. But the new full-up simulations by Macciò's group indicate that dark energy works after all. "If and only if you include dark energy, there is a very good agreement," Macciò says. "This is why we state that we have found the signature of dark energy." Not everyone agrees. In 1999 Rien van de Weygaert of the University of Groningen in the Netherlands and Yehuda Hoffman of Hebrew University in Jerusalem argued that the Local Volume is caught in a cosmic tug-of-war between surrounding galaxy clusters. This, too, would pull galaxies apart, offsetting their own gravity. To decide whether this mechanism or dark energy is more important, astronomers have to compare the Local Volume with similar regions. If those not caught in a tug-of-war behave similarly, the dark energy must be to blame. Unfortunately, the teams disagree on what "similar" means, so the debate goes on. If Macciò's model proves to be right, then dark energy, once considered the most "out there" idea in science, an ethereal abstraction of little relevance, will bump a little closer down to earth.

Sounds Guide Young Fish toward Home

Image: SCIENCE According to Dorothy, "there's no place like home." A new report suggests that for fish, no place sounds like home. Findings published today in the journal Science indicate that young fish, which can float out to sea during their larval stage, use sounds emanating from coral reefs to find their way back. Activities such as grinding fish teeth and snapping shrimp claws contribute to the din surrounding a coral reef, which can often be heard from distances up to a few kilometers away. To test whether the racket affected young fish, Stephen Simpson of the University of Edinburgh and his colleagues constructed 24 patches of artificial reef. The researchers outfitted half of them with speakers and broadcast recordings of reef noise, whereas the other half were kept silent. Of the two main types of fish attracted to the fake reefs, both cardinalfish and damselfish exhibited a preference for the louder reefs compared to the quiet ones. The two species did show differences in what types of noise they favored: damselfish were drawn more to higher-frequency sound, but cardinalfish exhibited no such preference.

The discovery that fish respond to reef sounds suggests a potentially valuable management tool, the authors say. "This is a significant step forward in our understanding of their behavior, which should help us to better predict how we should conserve or harvest populations of reef fishes in the future," Simpson remarks. "It should also alert policymakers to the damage that human activities like drilling and shipping may have on fish stocks because they drown out the natural clues given by animals." --Sarah Graham