For the first time, scientists have been able to view human thought processes directly, tracing the complex patterns of electrical and chemical reactions to small clusters of brain cells.
These unique glimpses of the brain at work are not the result of sophisticated new technologies that employ radioisotopes or X-rays to monitor brain activity.
Instead, the researchers used a comparatively simple camera that records subtle differences in reflected light -- too small to be seen with the naked eye -- that flicker. Washington researchers report in today's s edition of the British journal Nature that the technique will probably be used initially to identify areas of the brain that must be preserved during surgery to ease the symptoms of epilepsy.
In the longer term, they said, the technique will provide a much more precise way of mapping various thought processes and physical activities to specific locations on the brain.
"It's a very interesting technique," said Dr. William H. Theodore, a neurologist at the National Institute of Neurological Diseases and Stroke. "The advantage is that it records very rapid changes in brain function" that cannot be monitored in any other way.
"I think it might enable surgeons to better map out speech regions so that they can be preserved and left behind" during epilepsy surgery, said Dr. Robert S. Fisher, a neurologist at the Barrow Neurological Institute in Phoenix, Ariz., and secretary of the American Epilepsy Society.
Patients undergoing epilepsy surgery sometimes develop impairments of speech or movement or the loss of memory. "Any technique that allows preservation [of functional brain tissue] while removing as much epileptic tissue as possible is very valuable," Dr. Fisher added.
The technique, called optical imaging, "could be a very powerful research tool and is likely to have very real practical applications in brain mapping," said Dr. George Ojemann, a University of Washington neurosurgeon and head of the research team. "We're very excited about it because there is no other technique that can do what it can."
During the surgery, Dr. Ojemann's team shined reddish light on the brain and photographed it with a highly sensitive electronic imaging device called a charge-coupled device camera. A computer was then used to compare the picture taken during a mental activity to pictures taken before or after it.
By digitally subtracting one image from the other, the computer showed the areas where change has occurred and which were thus active.
No one is quite sure what causes the change in reflected light. Dr. Ojemann and his colleagues, Dr. Michael Haglund, a neurosurgeon, and Daryl Hochman, a computer specialist, speculate that the changes could result from increased blood flow to the active cells, increased uptake of oxygen, the appearance of products from a chemical reaction or perhaps some unknown cause.
The team has studied the technique on nearly 30 patients during brain surgery to alleviate the symptoms of intractable epilepsy. In the process, part of the skull is removed and the front surface of the brain exposed. Typically, surgeons use electrical currents applied through tiny electrodes scattered over the surface of the brain to identify which portions of the brain are most critical and must be preserved and which should be removed. Patients remain awake during the surgery to help surgeons identify the brain areas.