The collective activity of huge assemblies of brain cells, as reflected in their rhythmic electrical discharges, contributes to the derailed perceptions and thoughts of schizophrenia as well as to the heightened mental states achieved by experienced meditators, two new studies find.
Results from both investigations, slated to appear in the Proceedings of the National Academy of Sciences, coincide with earlier reports that a certain form of synchronized electrical activity in groups of brain cells fosters perception, memory, and consciousness (SN: 3/11/00, p. 167: Available to subscribers at Brain cells work together to pay attention).
All these studies rely on electroencephalogram (EEG) recordings of the rate and intensity at which cells on the brain's surface send messages. Of particular interest are the gamma waves produced when masses of neurons emit their electrical signals around 40 times a second.
Many neuroscientists suspect that gamma activity occurs when various chemical messengers foster efficient communication across large swaths of brain tissue.
"The absence of gamma activity is related to dysfunctional neural circuits that cause some of the core symptoms of schizophrenia," reports psychiatrist Robert W. McCarley of Harvard Medical School in Boston, who directed one of the new studies.
McCarley's team studied 20 people with schizophrenia and 20 who had no mental disorder. As EEG data were collected, participants looked at either of two computer-screen images containing four partial circles resembling open-mouthed Pacman figures. In one image, the shapes were placed and oriented to create the illusion of a square in the center of the figures. Each volunteer pressed a key to signal perception of the square.
Study volunteers with schizophrenia made substantially more errors and took longer to respond than the others did. During this task, only the mentally healthy volunteers exhibited gamma activity at the back of the brain, where much visual processing occurs. In the people with schizophrenia, neural synchronization also occurred but at a frequency below the gamma range, indicating weaker integration of critical neural networks. Those who had experienced intense hallucinations, delusions, and disorganized thinking showed the lowest-frequency synchronization.
Although the volunteers with schizophrenia had for years taken various antipsychotic medications that diminished their symptoms, none of the drugs had pushed neural synchrony into the gamma range.
John H. Krystal, a psychiatrist at Yale University School of Medicine, says he's "cautiously optimistic" that a focus on gamma activity will yield insights into how the brain malfunctions in schizophrenia.
In the second new study, directed by neuroscientist Richard J. Davidson of the University of Wisconsin–Madison, gamma activity gradually expanded across the brain during meditation by eight people skilled at the practice. These individuals had undergone Buddhism-based mental training for between 15 and 40 years. Meditators who had trained for the longest time displayed the most gamma activity.
Considerably smaller amounts of neural synchrony turned up during meditation in the brains of 10 college students who had just begun the practice. They had received a training session in meditation the week before testing and had then practiced the technique for 1 hour each day.
The experienced practitioners also exhibited substantially more gamma activity while at rest and not meditating than the students did. Further research needs to confirm that meditation training directly cultivates this brain response, rather than that people with high gamma activity are attracted to meditation, Davidson says.
These new findings are provocative but hard to interpret, remarks neuroscientist J. Anthony Movshon of New York University. "No one has convincingly linked gamma activity to any underlying brain mechanism involved in thinking or perception," Movshon says.
Nonetheless, neural synchrony "could be a gateway to understanding all sorts of mental activity," McCarley holds.
Richard J. Davidson
W.M. Keck Laboratory for Functional Brain Imaging and Behavior
University of Wisconsin, Madison
1500 Highland Avenue
Madison, WI 53703
John H. Krystal
Department of Psychiatry
Yale University School of Medicine
VA Connecticut Healthcare System (116-A)
950 Campbell Avenue
West Haven, CT 06516
Robert W. McCarley
Department of Psychiatry
Veterans Affairs Boston Healthcare System
Harvard Medical School
940 Belmont Street
Brockton, MA 02301
J. Anthony Movshon
New York University
Center for Neural Science
4 Washington Place, Room 809
New York, NY 10003