A System for Measuring Tremor Intensity in Rats

An accurate and physically defined system for measuring tremor in unanesthetized and unrestrained rats is described. The method is based on measuring the vibrations of an ordinary animal cage induced by the tremor of the animal inside it. The vibrations of the animal cage were recorded with a piezoelectric acceleration sensor and analyzed using a microprocessor on-line system. The computer was programmed in assembly language to perform a fast Fourier transform (FFT) spectrum analysis in real time. In those cases in which a frequency distribution curve is too complicated to handle, a mean value of all tremor components belonging to the different frequencies can be used. This mean value is called tremor intensity. Theoretical considerations using the spectral density distribution were employed to find a physically motivated measure of tremor intensity. The measuring system is carefully analyzed, and it is shown that the output of the system can be adjusted to give an estimate of the theoretically motivated measure of the tremor intensity. Measurements of some drug-induced tremor spectra are represented.