The technical development towards digital multi-channel EEG-devices is combined with advantages in data reproduction and display compared with paper- writing EEG-devices. This opens new possibilities of EEG registration and evaluation. Therefore the possibility of a non-invasive electroencephalographic examination of the awake standing horse was investigated. Based on the anatomical situation of the skull of the horse an electrode holding cape was developed. The uniform and easy repeatable electrode positioning makes it possible to register the EEG free of pain for the animal by using skin electrodes. In order to obtain an appropriate display of the EEG-activity as well as other sources of bioelectrical activity, recording programs with the crucial setting parameters were developed for a suitable data representation on the screen. This was a basic requirement to differentiate the electrical brain activity that is - on the head surface - in the lower µV-range from artefact influences which can not be avoided in the awake standing horse. The investigations were carried out in 22 horses in their usual environment (stable) on three different occasions. The visual evaluations of the EEG- traces on the screen as well as the quantitative data analysis on the computer were performed. The determination of the Hjorth-Parameters (activity, mobility, complexity) and the frequency spectra in 1-Hz-steps between 0 and 42Hz were carried out using 3 representative 4-second-segments for each EEG- record. Apart from finding reference parameters regarding positioning of the EEG-electrodes, the individuality of the EEG, known from human beings, could be found after repeated measurements in the adult horse during relaxed wakefulness. Furthermore single investigations on 14 foals showed that the EEG of the juvenile horse is significantly different from that of the adult horse. This agrees with the findings in humans where an adequate maturation of the electrical brain activity in children is known. Both the individuality and reproducibility in adult horses, as well as their differences to the EEG in foals, suggest that the use of this non-invasive method seems to be possible in the neurological diagnosis of pathological changes in the electrical brain activity in horses.
