Electrically induced blink reflex in horses.

This study investigates the blink reflex in horses when stimulated electrically. Through electromyography on 21 healthy, sedated horses, the researchers noted various responses related to the muscles controlling the eyelids.

Research Process

• The experiment involved the use of electrophysiology methods to study the blink reflex by applying electrical stimulation to the supraorbital nerve located at the supraorbital foramen.
• Surface electrodes were used for this electrical stimulation, and the responses were recorded from both the ipsilateral (same side) and contralateral (opposite side) orbicularis oculi muscles. These are the muscles that control the movement of the eyelids.
• Needle electrodes were inserted into the lateral aspect of the ventral eyelids to record these responses. The tests were conducted multiple times for each side of the face, maintaining a consistent stimulus intensity.

Findings

• The responses recorded were categorized into an early R1 response, a late response (R2 and Rc), and a third response (R3).
• The R1 response was recorded in the muscle on the same side as the electrode stimulation, reflecting its quick response to the stimulus.
• R2 and Rc were bilateral late responses. The R2 was recorded ipsilaterally (same side as the stimulus), while Rc was recorded contralaterally (opposite side).
• Finally, the R3 response was again recorded from the muscle on the same side as the electrode. It is particularly significant because in humans, this response is associated with pain sensation.
• All responses displayed polyphasic muscle potentials – the muscle potential varied in duration and amplitudes.
• R1 showed stable reflex latency similar to human reflex. R2 exhibited more variability both within and between individual horses. Rc, which was only found in 13 of the 21 horses, had a slightly longer latency than R2. R3 exhibited the most variable latency, and was recorded in 19 of the 21 horses.

Conclusion

• Given these results, further research could be taken to understand more about the reflexes in horses, specifically related to pain sensation, as the R3 is associated with pain sensation in humans, which opens avenues for better understanding pain response in equines.