Preparations used for membrane potential imaging. a Isolated trigeminal nerve-brainstem preparation. The dorsal side is shown at the front, and the sagittal sectional surface is shown by hatching. b Trigeminal nerve-attached brainstem sagittal slice preparation. The preparation was placed with the sagittal sectional surface upwards for measurement. Electric stimulation was applied by sucking the trigeminal nerve root with a suction electrode for all preparations. Sp5c spinal trigeminal subnucleus caudalis, V rootlet trigeminal nerve rootlet.