1997 年 63 巻 5 号 p. 687-691
The monitoring of neural signals of aquatic animals under freely behaving condition is essential to understand their neural mechanism of behavior. Here the authors introduce an underwater radio-telemetry system to receive electroencephalographic (EEG) signals from the fish freely swimming in freshwater areas. The system uses simple and generally available instrumentation method, and is composed of a transmitter and a receiver. The transmitter attached to the fish uses a 78-98 MHz main carrier frequency which is modulated by a 1.6 kHz pulse-frequency modulated subcarrier. It is radiated directly from the oscillating coil to the water, and travels from the subsurface transmitter to the receiver placed in the air. For receiving and demodulating the transmitted signals, a conventional FM broadcasting receiver is used with a frequency to voltage converter and a low-pass filter. The system transmitted high fidelity signals for several hours within a range of 5m. By using the system, EEG signals (olfactory bulbar wave) were successfully received for the first time from the fish (landlocked sockeye salmon Oncorhynchus nerka) freely swimming in an outdoor pond.
