Brain Source Imaging in Preclinical Rat Models of Focal Epilepsy using High-Resolution EEG Recordings

The overall goal of this procedure is to perform brain source analysis using high resolution EEG recordings obtained from rats with focal epilepsy. This is accomplished by first placing an EEG mini cap in distilled water with 0.2%chloride overnight and filling each electrode the next day with a mixed conductive paste to improve electrode impedance. The second step is to set the EEG mini cap on a sedated rat and record high resolution EEG data.

Next, the recorded EEG signals are pre-processed to obtain average signals for different types of interictal epileptiform using the threshold based method and the wavelet decomposition method. The final step is to generate the rat's head volume conductor model with the electrode positions based on either an individual or a probabilistic MRI. Ultimately, the ES Loretta inverse solution is computed to show the estimated brain sources that are expected to be related to the epileptogenic brain regions.

Preclinical RAM models are very useful to study epigenesis by mean of electrophysiological technique. Although invasive electrophysiological recording have been used in the past to study epileptic rat, there are no available technique to perform a whole brain source imaging in this rat without the needle anesthesia. In this study, we propose a whole methodology to achieve it.

In this video, I will show you how to prepare and set up the EEG mini. I will be in charge of all procedures ready to RU preparation for the recording. During a G recording, I will operate a G recording equipment and software.

In addition, I'll show how to perform brain source analysis from the recorded data. To begin this procedure mix EEG electrode paste with 0.9%NACL solution. Add a drop of methylene blue to help to visualize the electrode paste inside the electrodes and on the skin.

Next, place the mixed paste in a syringe and make sure that there are no air bubbles in it. Then fill all 32 electrodes with the paste from the bottom without introducing any air bubbles as part of the preparation procedure for the rat, trim the rat's head afterward, reduce the iso fluorine to 2%Then place the rat on the heating pad in the stereotaxic apparatus. Fix the ear canals with the ear bars and secure nose cone for the supply of anesthetic.

Next, apply ophthalmic ointment to the eyes of the animal. Subsequently shave its head and rub the skin with 90%isopropyl alcohol to stimulate the blood vessels and remove the grease. Then place a saline swab on the scalp and cover it completely to keep good skin conductance until the EEG mini cap is ready to be placed.

Connect the respiration temperature and three lead electrocardiogram probes to the rat's body to continuously monitor its physiology during the recording procedure. In this procedure, remove the saline swab on the rat scalp and place the prepared EEG mini cap on its skin. Fix the mini cap with rubber bands.

Apply a layer of high conductance electrode paste on both the ground and reference electrodes. Subsequently, place them on the respective ears. Then connect the EEG mini cap to the amplifier.

Look at a preview of the EEG traces and check the performance of all electrodes. Then administer Dexter at 0.25 milligrams per kilogram to the rat intraperitoneal, and immediately reduce the isof fluorine rate to 0%If the respiration rate is not within 30 to 60 BPM range, increase the isof fluorine rate gently at the maximum of 1%Now begin EEG recording and verify the existence of paroxysmal activity in the EEG traces. After the recording, mark the positions of the three jutting circles of the EEG mini cap on top of the skin by inserting a color pen inside them.

Before the EEG mini cap is removed, take a picture of the rat head with the landmarks. The IED detection and classification is performed Using the self-developed codes in matlab, the average EEG signals for each IED subtype are used for brain source analysis. In the following procedure, the open source software brainstorm will be used with the MRI atlas for Worcester rats, input MRI and brain surface to the software, generate the head surface with default setting.

Then generate the scalp and inner outer skull surfaces based on MRI For lead field computation, check the orientation and location of each surface with respect to the MRI, using the visualization option, using the acquired rat head picture to coregister the positions of the three landmarks in the MRI and the grid points of the landmarks. As references, generate the electrode positions as the electrodes are fixed on the scaffold. Then input the generated channel file to brainstorm software display, and confirm the location of all electrodes to compute lead field matrix.

Input the conductivity values, which satisfy the ratio of skin, skull, and brain. Obtain the lead field matrix based on the volume conductor model and the electrode positions created. After that, input the average EEG signals for an IED subtype by selecting the source estimation method option such as S Loretta.

The inverse solution will be obtained based on the computed lead field matrix and the input EEG signals at the end plot. The estimated sources shown here are the time series of the brain source locations of IEDs with respect to different clusters in spikes and sharp waves. The evaluation was performed at a specific time marked with a red vertical line.

Here are the EEG topographies, and here are the cortical current sources. This figure shows the estimated brain sources during seizure, the time instance are marked as red vertical lines. After watching this video, you should have a good understanding of how to prepare the easy mini cap to record high revolution EEG, and to conduct brain source analysis on the rat.

The methodology we presented here was applied to a clinical model to understand mechanisms on the underlying epigenesis.