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Research Findings

 

The Mind Revealed

By Marcia Barinaga

SCIENCE, Vol. 249 (1989)

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Some neuroscientists think that recently discovered oscillations of electrical potential at 40 hertz hold the key to how the brain assembles sense impressions into a single object.

Has Wolf Singer uncovered the cellular basis of consciousness? Some neuroscientists think he may have, although Singer himself stops short of such a bold claim.

It was in his recording that Singer noticed that, for short periods of less than half a second, the field potential was oscillating--alternately rising and dipping--with a frequency of 40 hertz. Those oscillations reflected a synchronous, repeating pattern of current flow into the neurons in the vicinity of the electrode. And since such an ion flow often triggers an action potential, that meant that many of those neurons must be firing action potentials together, in brief phase-locked synchrony.

"We think of consciousness as occurring in different ways," Crick says. "You can be conscious of pain; you can be self-conscious; you can be conscious of hearing, seeing, even of making plans. Our hypothesis is that all of these may have something in common and therefore why not study the easiest one? We think the easiest one is visual awareness."

One of the features that makes the 40 hertz oscillations attractive as a mediator of visual awareness, Koch says, is that their time scale corresponds with that of attention flitting from one object to another. The neurons typically stay phase-locked for several hundred milliseconds, which would allow them to make and break their liaisons in roughly the same period that a person's attention moves from one subject to the next.

As different subjects compete for attention, different sets of neurons may set up oscillations, Koch proposes. One wins momentarily and attention is briefly focused. Then that oscillation fatigues and attention is directed elsewhere. "It's a very beautiful picture," he enthuses. As the experimentalists pursue the oscillations in their biological context, the theorists are cheering from the sidelines. Von der Malsburg, for one, is eagerly awaiting the next round of results. "Wolf Singer and the others are onto something extremely important," he says. "If this experimental-theoretical story materializes even further, it will open the door to a completely new era."