Background: Short-duration electroencephalography (EEG) recordings in horses are helpful in diagnosing intracranial disorders. Potentially, long-duration ambulatory EEG (AEEG) recordings in horses will enhance the chance of detecting abnormal brain activity independent of the presence of an insult. Objective: The objective of this study was to test if AEEG recordings in unsedated horses can be acquired and benefit diagnosing abnormal brain activity. Animals and methods: Recordings were taken from 8 adult control horses and 10 patients suspected of intracranial abnormalities. Self-adhesive electrodes and the 'Porti-5' recording system were used. Filter settings were 0.5 Hz high pass and 35 Hz low pass. The records were analysed offline at a 50-200 mV/division and 10 seconds/division scale. Abnormal activity was defined as a spike or sharp wave, a period of generalised slow wave rhythmical activity or a generalised fast rhythmical discharge. The recording time ranged from 5 to 49 hours. Results: In the control group, one horse showed pathological activity. In the patient group, six out of nine horses showed abnormal activity during the recordings. Magnetic resonance imaging confirmed the presence of an intracranial mass in one patient. Long-term recordings of high quality can be obtained in unsedated horses by allowing daily activity using AEEG, resulting in a reasonable chance of recording (inter)ictal abnormal brain activity indicating epileptic or seizure-like activity in the absence of clinical signs or seizures. Conclusions: It is concluded that abnormal behaviour can be expressed intermittently, and with the availability of AEEG a useful tool is added to the diagnostic scenario for horses.

Epilepsy in the horse is diagnosed based on clinical signs, but diagnosing can be difficult if a grand mal is not present. The future prospects of the horse and potentially the safety of the owner depend on an accurate diagnosis. This review presents information on epilepsy and focuses on the diagnostic potential of (Ambulatory) electroencephalography ((A) EEG). An epileptic seizure is a brain disorder, which expresses itself as a recurrent episode of involuntary abnormal behaviour. The aetiology can originate from inside or outside the brain or is idiopathic. Besides those categories, seizures can be classified as generalised or partial. A typical generalised tonic-clonic seizure is characterised by the prodrome, the ictus and the post-ictal phase. EEG is the graphic recording of rhythmic bioelectric activity which originates predominantly from the cerebral cortex. In human medicine, the 10/20 international basis system for electrode placement is used. This makes comparison more reliable and consistent. The normal human brainwaves recorded are alpha, beta, theta and delta waves. In the horse, fewer descriptions of normal signals are available. In humans suffering from epilepsy, spikes, complexes, spike-and-wave discharges and rhythmical multi-spike activity are seen. In horses suffering from epilepsy, spikes, sharp waves and spike-and-wave discharges are seen. In humans, AEEG has numerous advantages above short-duration EEG in diagnosing epilepsy or intracranial pathology. In future, AEEG might be useful to record brain signals in awake horses expressing their behaviour under natural circumstances.