Optic nerve potentials and cortical potentials after stimulation of the anterior visual pathway during neurosurgery

The aim was to present cortical potentials after intraoperative electrical epidural stimulation of the optic nerve (ON) in individuals with normal preoperative vision. Optic nerve potentials after flash and electrical stimulation were additionally recorded. Contact electrodes on ON and occiput were used for monopolar recording of optic nerve potentials and cortical potentials, respectively. Epidural stimulating electrodes on ON were used to deliver a rectangular current pulse (intensity 0.2-5.0 mA; duration 0.1-0.3 ms; rate 2 Hz), and LED flash goggles were used for flash stimulation. Optic nerve potentials after flash stimulation predominantly consisted of a positive deflection with a latency around 40 ms, followed by a longer-lasting negativity with the peak at around 50 ms. Optic nerve potentials after electrical epidural stimulation of ON were comprised of a negative deflection at around 3 ms. A positive and a negative deflection at 20 and 30 ms, respectively, and a smaller positive deflection at 40 ms constituted cortical potentials after electrical epidural stimulation of ON. Stable and repeatable cortical potentials after electrical epidural stimulation of ON could safely be recorded in humans during neurosurgery. The origin of these presumably far-field potentials and their potential role in intraoperative monitoring remains to be established.