National Research Institute of Fisheries Engineering Director: M. Nakamura Research: Fishing gear and methods, boats and instruments for port engineering as well as for aquaculture National Research Institute of Aquaculture Director: T. Nose Research: Fish reproduction and development, fish pathology and nutrition; Nikko facilities-fresh water salmonoid fish biology, homing and migration; Ohmura facilities--bivalve growth and reproduction studies Science and Technology Agency (STA) Japan Marine Science & Technology Center (JAMSTEC) 2-15 Natsushima-cho Yokosuka City, Kanagawa-ken 237 President: N. Makimura Research: Oceanography and deep sea research, ocean energy and resources, undersea Mixed Enterprise Marine Biotechnology Institute Co., Ltd. 2-35-10 Hongo, Bunkyo-ku, Tokyo 113 Scientific Director: S. Miyachi Research: Exploring marine organisms for new products and processes THE FIRST INTERNATIONAL CONFERENCE ON BRAIN ELECTROMAGNETIC TOPOGRAPHY The conference, held in Osaka, Japan, focused on two major areas: the INTRODUCTION The conference, held in Osaka, Japan, on 12-14 September 1990 brought together leading scientists from over 23 nations. Although there have been seven international conferences on biomagnetism and four on topographic electroencephalography, this conference was broader in scope and included presentations on magnetoencephalography (MEG), electroencephalography (EEG), and evoked potentials (EP). The major theme of the conference was based on computer technology and mathematical and statistical procedures for analyzing and interpreting brain potentials in both normal human subjects and patients with clinical pathology. As the title states, this was the first International Congress of the New International Society for Brain Electromagnetic Topography. by J.W. Wolfe and S. Matsuoka brain recording (four by American scien- This report highlights the following There were 387 registered participants in attendance; approximately onehalf of these were from countries outside of Japan. Of the 400 authors listed in the program, 45% were from Japan. The conference was divided into 8 special BACKGROUND invited lectures, 3 major symposiums, 10 oral sessions, and 3 poster sessions. The eight special lectures (see the Appendix) were given by pioneers in the fields of magnetic and electrical The concept that human organisms emanate energy that cannot be directly measured but somehow is part of their persona has probably existed for many thousands of years. This theory reached one of its most structured forms in the late 1700s when the French physician Franz Mesmer proposed that the human body was polarized in a similar manner as a magnet and responded to an invisible fluid which permeated the whole universe. Mesmer believed that these poles could become misaligned and result in different disease processes. Treatment of these disorders involved exposure to iron rods or stroking by other individuals in order to realign the poles. The remnant of this theory is found in our language today as the term "mesmerized." However, with the development of physics, it became possible to demonstrate that whenever electrical current flows, a magnetic field is generated in the space surrounding the conductor. Since the transmission of information within the nervous system is due to ionic current flow, it follows that this process should lead to the development of “biomagnetic fields." Although it became possible in the early 1900s to use simple amplification systems to measure the electrical potentials generated by the depolarization of nerve cells and their axons, it was not until 1963 that the first reliable biomagnetic measurements were obtained (Ref 1). Baule and McFee used two side-by-side large coils to measure the magnetic field changes associated with the heart action in a human. In order to reduce the magnetic disturbances created by buildings and machinery, they made their measurements in a rural open field. In 1968, Cohen (Ref 2) developed a shielded room in order to decrease the magnetic background noise and was then able to detect and record magnetic fields from the brain. Magnetic fields associated with neural activity of the brain are extremely small and are one million to one billion times weaker than the earth's geomagnetic field. The most sensitive instrument for detecting magnetic fields is a device called a superconducting quantum interference device or SQUID. This device was first developed by physicists in order to measure extremely weak magnetic fields. The superconductors must be cooled to extremely low temperatures in order to become nonresistive to electron flow; therefore, liquid helium (approximately -269 °C) has typically been used as a cooling source. Figure 1 shows a typical arrangement of a SQUID device for detecting weak magnetic fields. As pointed out by Williamson and Kaufman (Ref 3, p. 476): If the detection coil consists of two identical loops of wire wound in opposite directions but separated by a few centimeters (called a "first-order gradiometer"), it will not respond to a field that is spatially uniform, because the positive signal imposed on one loop is just canceled by a negative signal of identical magnitude imposed on the second loop. Since the field from a distant source is fairly uniform, this technique discriminates against such sources. Yet the detection coil retains sensitivity to a nearby source, such as a human subject. dewar liquid helium SQUIDS detection coils Figure 1. Cutaway view of a 7-channel system for detecting biomagnetic signals. In recent years, gradiometers have been mounted back-to-back to provide second and third order gradiometers, which provide for increased rejection of unwanted signals. This improvement in technology has eliminated the need for very expensive shielded rooms and made the instruments more practical for both clinical and basic research settings. Figure 2 shows a subject seated under a 37-channel biomagnetic sensor system. Given the fact that it is possible to record magnetic potentials from the central nervous system, it is obvious that the critical question is how can these data be used to understand sensory processing of information in normal human subjects or subjects with brain pathology. Therefore, the major theme of this conference was the analysis and display techniques presently available for presenting multichannel data. TOPOGRAPHIC MAPPING Topographic mapping employs a number of analysis techniques for converting electrical (EEG or evoked potentials) or magnetic field potentials into two-dimensional and/or threedimensional displays. Typically, potentials from the brain are characterized by converting frequency and intensity information into power spectrums, which are then displayed in different colors on the color cathode ray tube. These two-dimensional maps provide a semiquantitative representation of the brain potentials and facilitate studies of the spatial distribution of the potentials (see Figure 3). In 1975, Ueno et al. (Ref 4) were among the first to develop this technology to the point that it was possible for an on-line computer system to provide automatic plots of topographic contour maps of the electroencephalogram (EEG). This system was subsequently made commercially available by the Nihon Kohden Kogyo Co. and later by the Nihon Denki Sanei Co. The availability of these systems led to a dramatic increase in the number of basic research and clinical studies conducted in Japan and abroad. |