Apparatus for monitoring those signals in the brain which give rise to electroencephalograms (EEG) is described. The apparatus is particularly applicable to the fetus where EEG signals often contain a component of those signals which give rise to electrocardiographs (ECG). In the apparatus ECG signals picked up by electrodes in an electrode assembly forming part of the apparatus are eliminated by deriving two signals having equal ECG components, the two signals being subtracted from one another to provide a signal representing EEG. The electrodes may be concentric annular electrodes, for example, or relatively small disc electrodes spaced apart at the vertices of an equilateral triangle.