Abstract: An apparatus for monitoring the activity level of an organ of the human body.The apparatus processes digital values recorded in the memory of a processor. These digital values correspond to the analog values of a differential signal supplied after amplification and filtration of activity signals supplied by sensors. The memory contains a program for processing the digital values by sampling during each period of a succession of periods shifted by a predetermined time interval. The program controls the calculation of the Fourier transform of these values during each period. The frequency spectrum of the input signal is obtained during each interval. During each interval the processor detects the peak of the spectrum relative to the organ to be studied, as well as the amplitude maximum of that peak. The processor supplies a signal representing the evolution of the maxima of the peaks for all the time intervals. This signal is characteristic of the activity level of the organ to be studied.