Preliminary investigation of somatosensory evoked potentials in equine headshaking.
Authors: Pickles K J, Gibson T J, Johnson C B, Walsh V, Murrell J C, Madigan J E
Journal: The Veterinary record
Summary
# Equine Headshaking: A Neurophysiological Window into Trigeminal Dysfunction Idiopathic headshaking in horses remains a frustrating clinical problem with poorly understood neurological origins, prompting researchers to investigate whether abnormalities in trigeminal nerve signalling might underpin the condition. Using somatosensory evoked potentials (SEPs)—a technique measuring electrical brain activity following controlled trigeminal nerve stimulation—investigators compared cortical responses in eight control horses and eight headshakers under general anaesthesia, recording potentials via subcutaneous needle electrodes and, in two cases, dural electroencephalography electrodes. Headshaking horses demonstrated significantly shortened middle latency and inter-peak intervals in their SEP waveforms compared to controls, suggesting functionally altered trigeminal nerve physiology rather than simple pain sensitivity differences. Whilst preliminary in scope, these findings provide the first direct neurophysiological evidence that headshaking may involve abnormal neural processing within the trigeminal system itself, potentially opening new diagnostic and therapeutic avenues. For practitioners, this work validates the neurological rather than purely behavioural or musculoskeletal basis of idiopathic cases, supporting investigation of neuromuscular therapies and trigeminal-targeted interventions in affected horses.
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Practical Takeaways
- •This neurophysiological technique may eventually provide a diagnostic tool to confirm trigeminal nerve involvement in headshaking cases, potentially leading to more targeted treatment approaches
- •The altered SEP parameters in headshaking horses provide objective neurological evidence supporting a peripheral nerve dysfunction basis for this condition rather than purely behavioral causes
- •Further development of this SEP methodology could help differentiate headshaking caused by trigeminal nerve pathology from other etiologies
Key Findings
- •Triphasic somatosensory evoked potentials (SEPs) were successfully recorded from equine cerebral cortex following maxillary trigeminal nerve stimulation
- •Headshaking horses demonstrated decreased middle latency intervals compared to control horses following trigeminal nerve stimulation
- •Headshaking horses showed decreased inter-peak intervals compared to control horses, suggesting abnormal trigeminal nerve physiology
- •SEP recording technique using subcutaneous needle electrodes proved feasible in anesthetized horses (8 horses) and dural electrodes in 2 horses