Imaging Method Reveals Remarkable 'Architecture' of the Working Brain


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REHOVOT, Israel - December 16, 1997 - With thousands of neurons firing signals in all directions and forming trillions of possible connections, you'd expect the working brain to be a messy place.

Yet a new study conducted by researchers from Max Planck Institute of Psychiatry in Martinsried, Germany, and Israel's Weizmann Institute of Science reveals that brain cells engaged in different tasks in the visual cortex form "mosaics" which are amazingly orderly and elegant.

The study, featured on the cover of December's Journal of Neuroscience, used the optical imaging method developed by Weizmann's Prof. Amiram Grinvald, which has made it possible to provide an extremely detailed map of how the brain is organized when it processes information.
"Our maps of the working brain are so orderly they resemble the street map of Manhattan rather than, say, of a medieval European town," says Dr. Mark Huebener of Max Planck.
Beyond allowing us to marvel at the beauty of the brain's design, this research may assist in the development of artificial vision systems.

"Over the course of evolution, the mammalian brain developed its sophisticated architecture not in order to provide scientists with pretty pictures but in order to function as efficiently as possible," says Grinvald."Once we fully understand the principles behind this efficiency, we may be able to use them in artificial systems," he says.
The research team included Dr. Huebener and Prof. Tobias Bonhoeffer of Max Planck Institute of Psychiatry, and Dr. Doron Shoham and Prof. Grinvald of the Weizmann Institute's Neurobiology Department.

A regular geometric pattern

In the new research and in two preceding studies conducted by Grinvald and colleagues, optical imaging was used to examine the spatial relationship between neurons responsible for three aspects of vision - perception of depth, shape and color - and revealed that they form remarkably orderly interrelated mosaic-like patterns.

Groups of neurons responsible for depth perception are organized in parallel columns, while the "shape-savvy" neurons form patterns resembling pinwheels (first visualized by Bonhoeffer and Grinvald). The centers of the pinwheels are aligned along the centers of the columns in relatively straight lines, as are the clusters of neurons responsible for color perception. Moreover, the pinwheels' "spokes" always cross the borders of the columns at a right angle.
Obviously, these regular geometric relationships between different groups of working neurons are governed by specific rules that are far from random and apparently serve to maximize the efficiency with which the brain processes visual information.

Extremely high resolution

Scientists have long suspected that, despite its overwhelming complexity, there is method to the brain's "madness": as long as 30 years ago, Nobel-winning neuroscientists Torsten Wiesel and David Hubel talked about the "architecture" of the brain at work."Architecture" implies that once we know how to look, we'll discover that the networks of functioning neurons form orderly structures depending on their task.

Yet until recently, brain imaging techniques did not provide sufficient resolution to reveal such structures.It was precisely for this purpose that Grinvald - while working in Prof. Wiesel's laboratory at Rockefeller University - developed the optical imaging method used in the current study.
Optical imaging makes it possible to visualize the detailed organization of the brain at work because it can map the brain's functional architecture with an extremely high resolution, allowing scientists to observe structures as small as 0.05 millimeter in size. In contrast, the resolution of other imaging methods is too low to accomplish this kind of mapping: functional magnetic resonance imaging, or f-MRI, provides a resolution of only 1-3 millimeters, and positron emission tomography, approximately 5 millimeters.All of these three imaging techniques are based on the interaction between the brain's electrical activity and the circulation of blood in its microvessels. In fact, optical imaging research is currently being used to improve the resolution of f-MRI.

Prof. Grinvald, who holds the Helen and Norman Asher Professorial Chair in Brain Research, is head of the Murray H. and Meyer Grodetsky Center for Research of Higher Brain Functions and of the Wolfson Center for Applied Scientific Research in Functional Brain Imaging at the Weizmann Institute.

This work was supported by the Max-Planck Gesellschaft and by grants from the Minerva Foundation, the Human Frontier Science Program, the European Commission Biotech Program, and Ms. Margaret Enoch of New York.


The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel.