A novel methodology to demonstrate vestibulo-ocular reflex using caloric stimulation in undergraduate physiology laboratory

The study aims to develop a novel methodology to demonstrate the vestibulo-ocular reflex (VOR) and nystagmus by caloric stimulation in an undergraduate medical physiology laboratory. The experimental setup involved two sets of electrodes: one set positioned laterally to both eyes, and another set positioned vertically over either the right or left eye. The caloric method is used to stimulate ears, which involves irrigation of warm (44 °C) and cold (30 °C) water into the ears while maintaining a temperature difference of approximately +/- 7 °C from the body temperature. The changes in corneoretinal potential were calibrated to angular displacement by two-point calibration method and angular velocity was derived after taking the first-time derivative. The results obtained from digital data acquisition system were compared to the traditional instrument used in our ENT department (Interacoustics Videonystagmography VNG system for hospitals, medical grade) for the normal subject's data. No significant differences in angular velocity were noted (p>0.05). The cold stimuli elicit a more pronounced VOR compared to the warm stimuli. It has been consistently observed that the onset of nystagmus occurs approximately 20 seconds after irrigation, reaching its peak intensity between 45 and 90 seconds, and gradually diminishing until it ceases after approximately 200 seconds. Our developed methodology enables recording and quantification of nystagmus using easily accessible equipment. This study serves the goal of visualizing physiological process of VOR and thereby, fulfils the goal of an effective teaching tool for demonstrating to undergraduate medical students.