Monitoring the Brain Cortex with a Multi-Electrode Array in Response to Seizure-Inducing Agents

Start with a brain slice containing the anterior cingulate cortex, or ACC, and the thalamus regions.

Using an anchor, secure the brain slice to a multi-electrode array or MEA chamber, an electric signal-measuring device perfused with oxygenated artificial cerebrospinal fluid.

Position transcranial direct-current stimulation or tDCS electrodes with one near the ACC and the other placed distal to the ACC to deliver direct current to the brain slice.

Record baseline signals and deliver electric current to the slice through tDCS.

Adjust the electrode length and the tDCS current to obtain quality signals.

Using a stimulating electrode, deliver pulses of current to the thalamus, which induces artificial seizure by stimulating the ACC.

Adjust the current to stimulate the thalamus-cingulate pathway, which connects the thalamus to the ACC, to obtain an optimal ACC response.

Record it through the MEA.

Infuse seizure-inducing drugs into the MEA chamber

Using stimulating electrodes, deliver electric pulses to the thalamus-cingulate pathway and record the drug-induced ACC response.

Confirm the placement of an MEA probe on the multichannel system. Use one tube to guide the ACSF into the MEA chamber and the other tube to guide the ACSF out of the chamber. Continuously perfuse the preparation with warm oxygenated ACSF at 30 degrees Celsius. Using a wet cotton swab, transfer a brain slice to the MEA.

Carefully move the brain slice to orient the ACC above the electrodes. Then, stabilize the brain slice with a slice anchor to ensure a good electrical connection between the slice and the electrodes. Afterward, place the anode electrode proximal to the ACC and the cathode electrode distal to the ACC. Record the field strength by the two field orientations of MEA. Then, deliver the electric currents using a stimulator.

Adjust the distance between the two silver chloride electrodes to about 1.5 to 2 centimeters, and adjust the stimulator's current strength to make the DCS between 0.5 and 2 milliamps. In this procedure, place a tungsten electrode in MT, and deliver pulses from the stimulator to the thalamic region of the slice. Next, use various current intensities to determine the threshold that elicits an ACC response.

Move the tungsten electrode along the thalamo-cingulate pathway to obtain the optimal response profile. Record 10 to 20 ACC responses, and use the software to automatically average all of the ACC responses evoked by empty stimulation.

To induce seizure-like activity, add 250 micromolar for AP and 5 micromolar bicuculline to the perfusion solution, and continue to perfuse the slice for 2 to 3 hours. Maintain the pump at a relatively fast perfusion rate, which can help prevent the buildup of a pH gradient. Next, place the tungsten electrode in MT, and deliver electrical stimulation to obtain an ACC response profile. Record 10 to 20 sweeps and average the responses. Afterward, replace the perfusion solution with fresh ACSF to wash out the drugs.