Recording of Visual Evoked Potentials via the Skull Electrodes in a Rat Model

Begin with an anesthetized, dark-adapted rat. Add a drug solution to the eyes to widen the pupils.

This allows more light to reach the retina, the light-sensitive layer with photoreceptors.

Make a skull incision to expose pre-implanted recording screw electrodes in the brain's visual cortex and a reference electrode at the midline.

Connect one of the visual cortex screw electrodes and the reference electrode to an amplifier for signal recording.

Next, insert a ground electrode into the tail to reduce electrical noise.

Position a light-stimulation device over the eye on the side opposite to the connected cortex screw electrode and then deliver the light flashes.

Retinal photoreceptors detect the light and convert it into electrical signals that travel along the optic nerve and transmit to the opposite visual cortex.

In the visual cortex, the pre-implanted electrode detects these signals and produces the electrical output generated by light stimuli, termed as visual evoked potentials, or VEPs.

After anesthetizing the animal and preparing the skin as before, transfer it to a dark room. There, maintain its body temperature within half a degree of 37 degrees Celsius using a homeothermic blanket system and a temperature probe. While being monitored, dark-adapt the animal for 5 to 30 minutes.

After half an hour, dilate the pupils with 1% tropicamide eyedrops. Then, using scissors and forceps, open the skin over the skull, and access the pre-placed in situ screw electrodes. Connect the screws to the impedance meter. Then, measure and maintain the electrode impedance below 5 kiloohms.

Now, connect the screw over the contralateral visual cortex of the stimulated eye. Next, insert a needle electrode into the tail to serve as the ground. Now, place a calibrated mini-Ganzfeld stimulator onto the skin around the eyelids to improve the eye isolation. Then, deliver photic stimulation using 100 flashes at 1 hertz, with low-pass filter at 1 hertz, and the high-band pass filter at 100 hertz.