The authors would like to thank Pedro A. Valdes Hernandez, Francois Tadel, and Lloyd Smith for their valuable advice and fruitful discussion. We also thank Rafael Torres for the proof reading.

Ethics statement: All experiments are performed following the policies established by the Institutional Animal Care and Use Committee (IACUC) at Florida International University (IACUC 13-004).
1. EEG Recordings
<ol>
	<li>Preparation of the EEG mini-cap
	<ol>
		<li>Immerse the electrode tips of the EEG mini-cap at least 12 hrs in distilled water with 0.2% chloride. Rinse the EEG mini-cap gently in distilled water. Dry the cap and the electrodes in the air.</li>
		<li>Mix EEG electrode paste with 0.9% NaCl solution in the volume proportion of 2 : 1. Add a drop of methylene blue, which will help to visualize the electrode paste inside the electrodes and on the skin. Take the mixed paste in a syringe. Make sure there are no air bubbles in the syringe. Inject the gel into each of the 32 electrodes, filling them without introducing any air bubbles. It is recommended to inject from the bottom rather than the top. This provides better access to each electrode and reduces the possibility of the gel spilling over.</li>
		<li>Turn on EEG and physiological recording system, and open the corresponding recording software on the computer in use.</li>
	</ol>
	</li>
	<li>Animal preparation and anesthesia 
	NOTE: Chronic epilepsy was created using a protocol for FCD8 in Wistar rats. The EEG recording were conducted in adult Wistar rats (8 weeks old, 300 - 400 g).
	<ol>
		<li>Record the rat&#8217;s weight in an experiment sheet. Use this information to calculate sedative dose (dexdomitor 0.25 mg/kg). Induce anesthesia in the rat with 5% isoflurane and 100% oxygen (1 L/min at 14.7 psi).</li>
		<li>After trim the rat&#8217;s head, reduce isoflurane to 2% and maintain it during the entire setting of the EEG mini-cap. Check rat reflexes are absent (toe-pinch).&#160;Place the rat on a heating pad in the stereotaxic apparatus by fixing the ear canals using ear bars. Make sure anesthesia nose cone is secure.</li>
		<li>Apply lubricant ophthalmic ointment to each eye.</li>
		<li>Shave the extra hair on the rat head and ears using a razor. Avoid any bleeding during shaving. 
		NOTE: Any hair left on the skin will produce noise in the EEG recordings. Rub the rat&#8217;s skin with 90% isopropyl alcohol to stimulate the blood vessels and degrease the skin.</li>
		<li>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.</li>
		<li>Connect temperature, respiration, and three lead electrocardiogram probes. Note that the temperature is measured by a rectal probe. Continuously monitor the physiology of the rat during the recording procedures. Ensure that the normal temperature is 37 &#176;C, respiration range is 30 - 60 breaths per minute, and heart rate is around 350 - 450 beats per minute .</li>
	</ol>
	</li>
	<li>Recording procedures
	<ol>
		<li>Remove the saline swab on the rat&#8217;s scalp and place the prepared EEG mini-cap on its skin. Fix the mini-cap with rubber bands. Place one rubber band on the front side of the scalp, usually in front of the eyes, and another band at the back of the scalp between the ears and neck. Use a plastic protector under the neck to facilitate normal respiration.</li>
		<li>Put a layer of high conductance electrode paste on both the ground and reference electrodes. Place them on the respective ear. 
		NOTE: The reference electrode can be possibly placed in other locations.</li>
		<li>Connect the EEG mini-cap to the amplifiers and observe a preview of the workbench for electrode impedance. Check the performance of all electrodes. For a high-quality recording, ensure that the impedance value is in the range of 5 - 30 k&#937;. If there are any noisy electrodes, provide better contact with the scalp by either moving them inside the scaffold toward the scalp or gently injecting more gel from the top of the electrode.</li>
		<li>Administer dexdomitor (0.25 mg/kg) intraperitoneally and immediately reduce isoflurane rate to 0%. If the respiration rate is not within 30 - 60 breaths per minute range, start increasing the isoflurane rate gently. Do not exceed the value of 1% isoflurane. Monitor this step carefully because the mixture of isoflurane and dexdomitor could prompt the animals to a critical condition. 
		NOTE: On the preclinical model of focal epilepsy, isoflurane affects IEDs, whereas dexdomitor does not. Subjects under isoflurane have weaker epileptogenic property, i.e., relatively fewer IEDs can be detected compared to other conditions7,14. The dexdomitor dose is effective for about 2 hrs. Thus, to save the time for its effect, the preparation was carried out under isoflurane.</li>
		<li>Conduct EEG recordings. 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. Use them as landmarks for MRI co-registration. Take a picture of the rat head with the landmarks. Place the rat back inside the cage and monitor it until complete recovery from dexdomitor&#8217;s effect. 
		NOTE: In this experiment, red color (opponent color to green) was used to distinguish from the electrode positions (green). However, it is recommended to use other colors (purple/green) if small bleeding spots are observed in the skin.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/52700/52700fig1.jpg" /> 
Figure 1. A picture of the EEG mini-cap placed on a particular rat.
<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700fig1highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Brain Source Imaging
<ol>
	<li>IED classification 
	NOTE: The IED detection and classification is performed using self-developed codes in MATLAB based on the previous study15. This software will be available by request.
	<ol>
		<li>Discard noisy channels by visually inspecting the EEG tracers. Remove EKG artifacts using an automatic method for periodic waveform subtraction, which is based on a template and a correlation analysis. 
		NOTE: Usually, the experimenter who recorded the EEG shares the written experimental sheet for the observed bad channel information based on the impedance values. Software to remove EKG artifacts will be also available by request. 
		<img alt="Figure 2" src="/files/ftp_upload/52700/52700fig2.jpg" /> 
		Figure 2. An example of the EEG trace showing different types of IEDs. The red box indicates one type of IEDs. 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700fig2highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a> 
		&#160;</li>
		<li>Apply a band-pass filter with cutoff frequencies of 3 - 150 Hz and a notch filter to remove the line frequency (60 Hz in general and 50 Hz in some countries) component offline.</li>
		<li>Detect two types of IEDs (spikes and sharp-waves). Spikes and sharp-waves constitute large electrical events of 20 - 70 ms and 70 - 200 ms in duration respectively. Therefore, after applying a respective band-pass filter (cutoff frequencies of 15 - 50 Hz for spikes and 5 - 15 Hz for sharp-waves), the IEDs are detected based on amplitude thresholds15. 
		NOTE: The thresholds are automatically set to 4&#963; as suggested in the previous study for multiunit activity15. Here, &#963; is an estimated standard deviation of the bandpass-filtered signal, &#963; = median{|filtered signal| &#8260; 0.6745}.</li>
		<li>Sub-classify spikes and sharp-waves into different clusters. The distinctive features of different spikes and sharp-waves are extracted using wavelet transform15. They are sub-classified into multiple clusters using k-means, and the optimal cluster number k is determined using silhouette.</li>
		<li>Average the sub-classified signals within the same cluster. The average EEG signals for each IED sub-type will be used for brain source analysis.</li>
	</ol>
	</li>
	<li>Volume conductor model 
	NOTE: For the following sections, the open source software, Brainstorm12, will be used with the MRI atlas for Wistar rats9. However, individual rat&#8217;s MRI can also be used to generate the volume conductor model if available. The MRI atlas9 can be downloaded at 
	<a href="http://www.idac.tohoku.ac.jp/bir/en/db/rb/101028.html">http://www.idac.tohoku.ac.jp/bir/en/</a>. This website provides the atlas as NIFTI format under &#8220;Wistar Rat MRI Atlas&#8221; section, and it can be accessible after registration. The software needed for pre-processing can be also found in this website.
	<ol>
		<li>Input MRI and brain surface to the software12. 
		<img alt="Visual 1" src="/files/ftp_upload/52700/52700vis1.jpg" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis1highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Generate head surface with default setting. 
		<img alt="Visual 2" src="/files/ftp_upload/52700/52700vis2.jpg" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis2highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Generate scalp and inner/outer skull surfaces based on MRI for lead field computation12. 
		NOTE: The resolution of the vertices influences the accuracy of the estimated source, but large number of vertices results in high computational complexity. Recommended number of vertices of each layer is 642 for acceptable accuracy with fair computational complexity. The thickness of the skull can be checked from the MRI, and in the case of the MRI atlas, it is approximately 1 mm. After inserting above values in the software, corresponding triangle face-vertex meshes for each surface will be created. 
		<img alt="Visual 3" src="/files/ftp_upload/52700/52700vis3.jpg" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis3highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Check the orientation and location of each surface with respect to the MRI using the visualization option. Modify accordingly, if any surfaces are not co-registered12. 
		<img alt="Visual 4" height="351" src="/files/ftp_upload/52700/52700vis4.jpg" width="321" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis4highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Using the rat head picture acquired in 1.3.5. co-register the positions of the 3 landmarks (R1, R2, and R3) in the MRI. Use the grid points of the landmarks as references to generate the electrode positions as the electrodes are fixed on the scaffold (Figure 3B). 
		<img alt="Figure 3" src="/files/ftp_upload/52700/52700fig3.jpg" /> 
		Figure 3. (A) Rat head picture used to obtain electrode positions and (b) the EEG mini-cap diagram with the coordinate system. Red dots in (A) indicate the landmarks mentioned in 1.3.5. which correspond to the red numbers in (B). Also, the green marks in (A) depict the 32 electrode positions, and they correspond to the blue numbers in (B). 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700fig3highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a> 
		&#160;</li>
		<li>Generate N &#215; 3 electrode position matrix based on the 3 landmarks. Here, N is the number of channels (N = 32) and the column represents the corresponding x, y, and z coordinate values. 
		NOTE: The EEG mini-cap is a rigid scaffold. Therefore, once the 3 reference grids (R1, R2, and R3) are obtained, the position of the electrodes are automatically set. The user will only need to redefine the Z-values on a way that the mini-cap is appropriately projected on the scalp. The N point grids can be numbered sequentially as depicted in Figure 3B blue numbers. The standard scaffold for the EEG mini-cap is commercially available (Table of Materials). The software for co-registration is also available to the community.</li>
		<li>Input the generated channel file. 
		<img alt="Visual 5" src="/files/ftp_upload/52700/52700vis5.jpg" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis5highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Display and confirm the location of all electrodes. Modify any misplaced electrodes12. The final coordinate system for the electrode positions should coincide with the coordinate system used for the above-mentioned surfaces. 
		NOTE: The created surfaces can be visually inspected on an MRI by using the visualization option, &#8220;MRI registration\Check MRI/surface registration.&#8221; And then, a selected surface will be displayed as yellow line on the MRI. In addition, the 3 landmarks and the 32 electrode positions can be displayed on the MRI by selecting the toolbox&#8217;s option, &#8220;Display Sensors\MRI Viewer.&#8221; The locations can be visually inspected by comparing the distributions based on the rat&#8217;s eye and ear locations (Figure 4). 
		<img alt="Figure 4" src="/files/ftp_upload/52700/52700fig4.jpg" /> 
		Figure 4. (A) MRI atlas with co-registered brain surface (yellow line), (B) the created volume conductor model with the aligned 32 electrodes and 3 landmarks (red dots), and (C) MRI atlas with co-registered reference grid R1. 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700fig4highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
	</ol>
	</li>
	<li>Brain Source Imaging
	<ol>
		<li>Compute lead field matrix13. Input the conductivity values which satisfy the ratio of skin, skull, and brain as 1 : 1/80 : 1. Obtain the lead field matrix based on the volume conductor model and the electrode positions created in 2.2. 
		NOTE: The toolbox12 offers the interface with the other software to compute BEM10. Therefore, only the conductivity values are required as input. 
		<img alt="Visual 6" src="/files/ftp_upload/52700/52700vis6.jpg" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis6highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Input the average EEG signals for each IED sub-type stored in 2.1.4. 
		<img alt="Visual 7" src="/files/ftp_upload/52700/52700vis7.jpg" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis7highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Obtain sLORETA solution13 based on the computed lead field matrix and the input EEG signals. By selecting the source estimation method option, the inverse solution can be obtained12. 
		<img alt="Visual 8" src="/files/ftp_upload/52700/52700vis8.jpg" /> 
		<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700vis8highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a></li>
		<li>Plot the estimated sources.</li>
	</ol>
	</li>
</ol>

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No conflicts of interest declared.

A new methodology to non-invasively record multichannel EEG in a particular preclinical model of focal epilepsy is described. The particulars for the recording and analysis procedures, with specific experimental tips, are provided. There were key factors to consider achieving successful results. First, for EEG recordings, obtaining high quality signals is essential. Proper viscosity of the EEG paste should be applied to each electrode during the mini-cap preparation, and the rat&#8217;s head and ear hair should be completely removed during shaving. Impedance check is the most important step to confirm the quality of EEG recordings. Second, for brain source imaging, generating proper volume conductor model is crucial. Each surface should be co-registered. Also, the generated electrode positions should have minimum distance error from the actual electrode locations on the rat&#8217;s scalp.
Even though this manuscript introduces source analysis procedures using Brainstorm12, they can be conducted using other open softwares16,17 and commercial products18,19. Also, besides sLORETA13, other inverse solutions such as multiple dipole models and Beamformer can be applied4.
One limitation of this approach is that behavior analysis cannot be conducted since the EEG recording is carried out under sedation. However, compared to the other methods for EEG recording in rats5,6, this approach is noninvasive.
Our preliminary results support the importance for a precise classification of IED markers from EEG recordings to determine the irritative zones in a rat with focal epilepsy, as well as to evaluate their relationship with the underlying mechanisms for seizure initiation11. In addition, it has been shown that EEG source localization for such specific IEDs showed a good correspondence with the respective BOLD activation and deactivation regions20.
Our study will stimulate the use of preclinical models to evaluate bed-bench-bed strategies developed by biomedical engineers. For example, IED extraction is nowadays performed in hospitals manually, which required a considerable human effort. The methodology proposed in this study does it automatically. We hypothesize that the use of this methodology will produce similar results when applied to patients with FCD. We are preparing IRB protocols for the evaluation of this and other aspects of the methodology in human dataset.
Moreover, the use of preclinical models will help us understand the capabilities and limitations of EEG source localization in epilepsy21. Accurate estimation of brain sources underling epileptogenesis is crucial for therapeutic strategies and surgical planning. Also, having a standard platform for EEG recording in rats will be useful for the evaluation of the effectiveness of several anti-epileptic drugs in preclinical trials. This is the first study in which epileptic rats are recorded non-invasively under sedation, which will open new doors for the evaluation of EEG biomarkers for epilepsy. However, the entire methodology presented in this study is extendable to other experimental conditions and brain disorders. The EEG mini-cap can be also used in other rodent&#8217;s types.
In the past, a forepaw stimulation paradigm in Wistar rats has been used to evaluate the quality and reproducibility of data recorded with the EEG mini-cap2. Moreover, validations for the brain source reconstruction have been performed from high-resolution skull EEG concurrently recorded with laminar local field potentials from Wistar rats under a whisker stimulation paradigm22. This methodology has been developed for Wistar rats because of the existence of an MRI atlas for this particular rat strain. However, it can be applied to other rodent types with their standard format of atlas including mouse23, Sprague-Dawley rats24, and Paxinos and Watson rats25. In addition, the fundamental procedures of our proposed methodology could be used in any rodent preclinical models for which EEG is an important modality. However, many aspects of this methodology are particularly for epilepsy, especially those related to EEG preprocessing (IED detection and classification). Also, researchers must be aware of proper drugs used for sedation in different cases. The use of isoflurane and dexdomitor in our study has been carefully considered due to the reduced impact on IEDs. Regarding EEG recordings, in the case of mouse, the relatively small scalp surface area would reduce the number of channels considerably.

It has been shown that interictal epileptiform discharges (IEDs) observed from EEG constitute useful markers of epileptogenesis in patients with focal epilepsy3. The regions inside the brain from which these IEDs originate, named irritative zones, can in practice be localized based on EEG recordings4. Preclinical models are essential to find correlates between these irritative zones and the actual regions underlying seizure initiation. However, recording EEG from small animals is challenging because of the small surface area of the head compared to the human scalp. Although invasive methods for chronic recording in rats can be used5, 6, techniques are not available at this moment to acquire traditional EEG recordings on rodents under acute conditions without the need of anesthesia.
To solve this problem, we apply a patented EEG mini-cap2, which allows us to record 32-channel EEG data from rodents noninvasively. In this study, we also provide evidence about the need of an analgesic to preserve IED frequency. Therefore, although fixation of EEG mini-cap was performed under isoflurane, EEG recordings were obtained with rats only under sedation (dexdomitor)7. The method proposed in this study can be used in any preclinical rat model of focal epilepsy. To illustrate the capabilities of this methodology, we apply it to understand the correlates between irritative and seizure-onset zones in focal cortical dysplasia (FCD). To that end, we use a &#8220;double-hit&#8221; model of FCD8 in Wistar rats.
To perform brain source analysis, it is required to: a) accurately extract IEDs from EEG raw data and b) obtain a volume conductor model for the individual animal head. To generate a practical volume conductor model, we use an in vivo rat MRI atlas, comprising average images of intensity/shape and obtained via non-linear registration of T2 images of 31 Wistar rats9. The forward model for the generated volume conductor was computed by boundary element method (BEM)10. As in the case of humans, two typical patterns of IEDs (sharp-waves and spikes) were detected and sub-classified into different clusters through an intelligent feature extraction, feature selection, and classification process11. These sub-classified signals are used to estimate the brain source localizations associated with different types of irritative zones. We present the source analysis steps using a well-known public software called Brainstorm12. The EEG source localizations for each IED sub-type and the seizure onset time frames were performed using standardized low-resolution brain electromagnetic tomography (sLORETA)13, which is available in Brainstorm.

<table><tbody><tr><td>Data Acquisition Computer</td><td>Hewlett-Packard</td><td>Z210 Workstation</td><td></td></tr><tr><td>Dexdomitor</td><td>Orion Pharma</td><td>6295000</td><td>Dexmedetomidine hydrochloride</td></tr><tr><td>EEG Analysis Software</td><td>The Mathworks Inc.</td><td>MATLAB R2011b</td><td></td></tr><tr><td></td><td></td><td>Brainstorm</td><td>Sylvain et al. 2001</td></tr><tr><td></td><td></td><td>OpenMEEG</td><td>Gramfort et al. 2010</td></tr><tr><td>EEG Data Streamer</td><td>Tucker-Davis Technologies</td><td>RS4 Data Streamer</td><td></td></tr><tr><td>EEG Electrode Paste</td><td>Biotach</td><td>YGB 103</td><td></td></tr><tr><td>EEG Preamplifier</td><td>BioSemi</td><td>Active Two</td><td></td></tr><tr><td></td><td>Brain Products</td><td>BrainAmp</td><td></td></tr><tr><td></td><td>Tucker-Davis Technologies</td><td>PZ3 Low Impedance Amplifier</td><td></td></tr><tr><td>EEG Recording Software</td><td>BioSemi</td><td>ActiView</td><td></td></tr><tr><td>EEG Recording Software</td><td>Tucker-Davis Technologies</td><td>OpenEx - OpenDeveloper</td><td></td></tr><tr><td>EEG SCSI Connector</td><td>BioSemi</td><td>Active Two SCSI Connector</td><td></td></tr><tr><td></td><td>Brain Products</td><td>D-sub Connector</td><td></td></tr><tr><td>EEG Processor</td><td>Tucker-Davis Technologies</td><td>RZ2 BioAmp Processor</td><td></td></tr><tr><td></td><td>Tucker-Davis Technologies</td><td>Zif-Clif Digital Headstage</td><td></td></tr><tr><td>High Resolution EEG Mini-cap</td><td>Cortech Solutions</td><td>DA-AR-ELRCS32</td><td>US patent Application No. 13/641,834</td></tr><tr><td>Isoflurane, USP</td><td>VedcoPiramal Healthcare</td><td>NDC 66794-013-25</td><td></td></tr><tr><td>Isopropyl Alcohol</td><td>Aqua Solutions</td><td>3112213</td><td>90% v/v solution</td></tr><tr><td>Lubricant Ophthalmic Ointment</td><td>Rugby</td><td>NDC 0536-6550-91</td><td>Sterile</td></tr><tr><td>NaCl</td><td>Abbott</td><td>2B8203</td><td>Vaterinary 0.9% Sodium Chroride Injection USP</td></tr><tr><td>Physiology Recording Software</td><td>ADInstruments</td><td>LabChart 7.0</td><td></td></tr><tr><td>Physiology Recording System</td><td>ADInstruments</td><td>PowerLab 8/35</td><td></td></tr><tr><td>Syringe</td><td>Monoject</td><td>200555</td><td>12cc</td></tr></tbody></table>

brain source imaging in preclinical rat models of focal epilepsy using high-resolution eeg recordings

Electroencephalogram (EEG) has been traditionally used to determine which brain regions are the most likely candidates for resection in patients with focal epilepsy. This methodology relies on the assumption that seizures originate from the same regions of the brain from which interictal epileptiform discharges (IEDs) emerge. Preclinical models are very useful to find correlates between IED locations and the actual regions underlying seizure initiation in focal epilepsy. Rats have been commonly used in preclinical studies of epilepsy1; hence, there exist a large variety of models for focal epilepsy in this particular species. However, it is challenging to record multichannel EEG and to perform brain source imaging in such a small animal. To overcome this issue, we combine a patented-technology to obtain 32-channel EEG recordings from rodents2 and an MRI probabilistic atlas for brain anatomical structures in Wistar rats to perform brain source imaging. In this video, we introduce the procedures to acquire multichannel EEG from Wistar rats with focal cortical dysplasia, and describe the steps both to define the volume conductor model from the MRI atlas and to uniquely determine the IEDs. Finally, we validate the whole methodology by obtaining brain source images of IEDs and compare them with those obtained at different time frames during the seizure onset.

&#160;Once all procedures are properly completed, estimated sources can be visualized in the brain surface of the pre-clinical model. Figure 5 shows the estimated sources from one particular sub-type of spikes (top) and sharp-waves (bottom) from IEDs. In addition, Figure 6 displays how the source distribution changes in sequential time frames during a seizure establishment. These results support the capability of the proposed methodologies to record high-resolution EEG on rats with focal epilepsy and to conduct source analysis using the recorded EEG.
<img alt="Visual 6" src="/files/ftp_upload/52700/52700fig5.jpg" />
Figure 5. Estimated brain source locations of IEDs with respect to different clusters in spikes (top) and sharp-waves (bottom). (A) Time series, (B) EEG topography, and (C) cortical current sources. The evaluation is performed at a specific time marked with a red vertical line in (A). 
<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700fig5highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a> 
<img alt="Visual 6" src="/files/ftp_upload/52700/52700fig6.jpg" /> 
Figure 6. Estimated brain sources during seizure.&#160;The time instants are marked as red vertical lines. 
<a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/52700/52700fig6highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Brain Source Imaging in Preclinical Rat Models of Focal Epilepsy using High-Resolution EEG Recordings at JoVE.com

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

This video introduces the preparation, recording, and source analysis procedures of high-resolution EEG on sedated rats with a particular preclinical model of focal epilepsy under noninvasive conditions.

Electroencephalogram (EEG) has been traditionally used to determine which brain regions are the most likely candidates for resection in patients with ...

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Nanyang Technological University

Research

JoVE Journal

Medicine

15.2K Views.  Florida International University. This video introduces the preparation, recording, and source analysis procedures of high-resolution EEG on sedated rats with a particular preclinical model of focal epilepsy under noninvasive conditions.

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

Simultaneous fMRI and Electrophysiology in the Rodent Brain

To examine the neural basis of the blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) signal, we have developed a rodent model in which functional MRI data and in vivo intracortical recording can be performed simultaneously. The combination of MRI and electrical recording is technically challenging because the electrodes used for recording distort the MRI images and the MRI acquisition induces noise in the electrical recording. To minimize the mutual interference of the two modalities, glass microelectrodes were used rather than metal and a noise removal algorithm was implemented for the electrophysiology data. In our studies, two microelectrodes were separately implanted in bilateral primary somatosensory cortices (SI) of the rat and fixed in place. One coronal slice covering the electrode tips was selected for functional MRI. Electrode shafts and fixation positions were not included in the image slice to avoid imaging artifacts. The removed scalp was replaced with toothpaste to reduce susceptibility mismatch and prevent Gibbs ringing artifacts in the images. The artifact structure induced in the electrical recordings by the rapidly-switching magnetic fields during image acquisition was characterized by averaging all cycles of scans for each run. The noise structure during imaging was then subtracted from original recordings. The denoised time courses were then used for further analysis in combination with the fMRI data. As an example, the simultaneous acquisition was used to determine the relationship between spontaneous fMRI BOLD signals and band-limited intracortical electrical activity. Simultaneous fMRI and electrophysiological recording in the rodent will provide a platform for many exciting applications in neuroscience in addition to elucidating the relationship between the fMRI BOLD signal and neuronal activity.

We have developed a method for simultaneous functional magnetic resonance imaging and electrophysiological recording in the rodent brain, providing a platform for the investigation of the relationship between neural activity and the blood oxygenation level dependent (BOLD) MRI signal.

To examine the neural basis of the blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) signal, we have developed a rodent model in ...

Neuroscience

Long-term Continuous EEG Monitoring in Small Rodent Models of Human Disease Using the Epoch Wireless Transmitter System

Many progressive neurologic diseases in humans, such as epilepsy, require pre-clinical animal models that slowly develop the disease in order to test interventions at various stages of the disease process. These animal models are particularly difficult to implement in immature rodents, a classic model organism for laboratory study of these disorders. Recording continuous EEG in young animal models of seizures and other neurological disorders presents a technical challenge due to the small physical size of young rodents and their dependence on the dam prior to weaning. Therefore, there is not only a clear need for improving pre-clinical research that will better identify those therapies suitable for translation to the clinic but also a need for new devices capable of recording continuous EEG in immature rodents. Here, we describe the technology behind and demonstrate the use of a novel miniature telemetry system, specifically engineered for use in immature rats or mice, which is also effective for use in adult animals.

Here we demonstrate the use of a wireless enabling technology for electroencephalogram (EEG) in neonatal rodent models of human disease. With telemetry, there are no encumbering connections, thus allowing natural behaviors.

Many progressive neurologic diseases in humans, such as epilepsy, require pre-clinical animal models that slowly develop the disease in order to test ...

Non-restraining EEG Radiotelemetry: Epidural and Deep Intracerebral Stereotaxic EEG Electrode Placement

Implantable EEG radiotelemetry is of central relevance in the neurological characterization of transgenic mouse models of neuropsychiatric and neurodegenerative diseases as well as epilepsies. This powerful technique does not only provide valuable insights into the underlying pathophysiological mechanisms, i.e., the etiopathogenesis of CNS related diseases, it also facilitates the development of new translational, i.e., therapeutic approaches. Whereas competing techniques that make use of recorder systems used in jackets or tethered systems suffer from their unphysiological restraining to semi-restraining character, radiotelemetric EEG recordings overcome these disadvantages. Technically, implantable EEG radiotelemetry allows for precise and highly sensitive measurement of epidural and deep, intracerebral EEGs under various physiological and pathophysiological conditions. First, we present a detailed protocol of a straight forward, successful, quick and efficient technique for epidural (surface) EEG recordings resulting in high-quality electrocorticograms. Second, we demonstrate how to implant deep, intracerebral EEG electrodes, e.g., in the hippocampus (electrohippocampogram). For both approaches, a computerized 3D stereotaxic electrode implantation system is used. The radiofrequency transmitter itself is implanted into a subcutaneous pouch in both mice and rats. Special attention also has to be paid to pre-, peri- and postoperative treatment of the experimental animals. Preoperative preparation of mice and rats, suitable anesthesia as well as postoperative treatment and pain management are described in detail.

Non-restraining EEG radiotelemetry is a valuable methodological approach to record in vivo long-term electroencephalograms from freely moving rodents. This detailed protocol describes stereotaxic epidural and deep intracerebral electrode placement in different brain regions in order to obtain reliable recordings of CNS rhythmicity and CNS related behavioral stages.

Implantable EEG radiotelemetry is of central relevance in the neurological characterization of transgenic mouse models of neuropsychiatric and ...

High-density Electroencephalographic Acquisition in a Rodent Model Using Low-cost and Open-source Resources

Advanced electroencephalographic analysis techniques requiring high spatial resolution, including electrical source imaging and measures of network connectivity, are applicable to an expanding variety of questions in neuroscience. Performing these kinds of analyses in a rodent model requires higher electrode density than traditional screw electrodes can accomplish. While higher-density electroencephalographic montages for rodents exist, they are of limited availability to most researchers, are not robust enough for repeated experiments over an extended period of time, or are limited to use in anesthetized rodents.1-3 A proposed low-cost method for constructing a durable, high-count, transcranial electrode array, consisting of bilaterally implantable headpieces is investigated as a means to perform advanced electroencephalogram analyses in mice or rats.

Procedures for headpiece fabrication and surgical implantation necessary to produce high signal to noise, low-impedance electroencephalographic and electromyographic signals are presented. While the methodology is useful in both rats and mice, this manuscript focuses on the more challenging implementation for the smaller mouse skull. Freely moving mice are only tethered to cables via a common adapter during recording. One version of this electrode system that includes 26 electroencephalographic channels and 4 electromyographic channels is described below.

Instructions for the low-cost construction and surgical implantation of a chronic transcranial high-density electroencephalographic montage into mice are provided. Signal recording, extraction, and processing techniques are also described.

Advanced electroencephalographic analysis techniques requiring high spatial resolution, including electrical source imaging and measures of network ...

Concurrent Recording of Co-localized Electroencephalography and Local Field Potential in Rodent

Although electroencephalography (EEG) is widely used as a non-invasive technique for recording neural activities of the brain, our understanding of the neurogenesis of EEG is still very limited. Local field potentials (LFPs) recorded via a multi-laminar microelectrode can provide a more detailed account of simultaneous neural activity across different cortical layers in the neocortex, but the technique is invasive. Combining EEG and LFP measurements in a pre-clinical model can greatly enhance understanding of the neural mechanisms involved in the generation of EEG signals, and facilitate the derivation of a more realistic and biologically accurate mathematical model of EEG. A simple procedure for acquiring concurrent and co-localized EEG and multi-laminar LFP signals in the anesthetized rodent is presented here. We also investigated whether EEG signals were significantly affected by a burr hole drilled in the skull for the insertion of a microelectrode. Our results suggest that the burr hole has a negligible impact on EEG recordings.

This protocol describes a simple method for concurrent recording of co-localized electroencephalography (EEG) and multi-laminar local field potential in an anesthetized rat. A burr hole drilled in the skull for the insertion of a microelectrode is shown to produce negligible distortion of the EEG signal.

Although electroencephalography (EEG) is widely used as a non-invasive technique for recording neural activities of the brain, our understanding of the ...

Recording and Modulation of Epileptiform Activity in Rodent Brain Slices Coupled to Microelectrode Arrays

Temporal lobe epilepsy (TLE) is the most common partial complex epileptic syndrome and the least responsive to medications. Deep brain stimulation (DBS) is a promising approach when pharmacological treatment fails or neurosurgery is not recommended. Acute brain slices coupled to microelectrode arrays (MEAs) represent a valuable tool to study neuronal network interactions and their modulation by electrical stimulation. As compared to conventional extracellular recording techniques, they provide the added advantages of a greater number of observation points and a known inter-electrode distance, which allow studying the propagation path and speed of electrophysiological signals. However, tissue oxygenation may be greatly impaired during MEA recording, requiring a high perfusion rate, which comes at the cost of decreased signal-to-noise ratio and higher oscillations in the experimental temperature. Electrical stimulation further stresses the brain tissue, making it difficult to pursue prolonged recording/stimulation epochs. Moreover, electrical modulation of brain slice activity needs to target specific structures/pathways within the brain slice, requiring that electrode mapping be easily and quickly performed live during the experiment. Here, we illustrate how to perform the recording and electrical modulation of 4-aminopyridine (4AP)-induced epileptiform activity in rodent brain slices using planar MEAs. We show that the brain tissue obtained from mice outperforms rat brain tissue and is thus better suited for MEA experiments. This protocol guarantees the generation and maintenance of a stable epileptiform pattern that faithfully reproduces the electrophysiological features observed with conventional field potential recording, persists for several hours, and outlasts sustained electrical stimulation for prolonged epochs. Tissue viability throughout the experiment is achieved thanks to the use of a small-volume custom recording chamber allowing for laminar flow and quick solution exchange even at low (1 mL/min) perfusion rates. Quick MEA mapping for real-time monitoring and selection of stimulating electrodes is performed by a custom graphic user interface (GUI).

We illustrate how to perform recording and electrical modulation of 4-aminopyridine-induced epileptiform activity in rodent brain slices using microelectrode arrays. A custom recording chamber maintains tissue viability throughout prolonged experimental sessions. Live electrode mapping and selection of stimulating pairs are performed by a custom graphical user interface.

Temporal lobe epilepsy (TLE) is the most common partial complex epileptic syndrome and the least responsive to medications. Deep brain stimulation (DBS) ...

Equipment Setup and Artifact Removal for Simultaneous Electroencephalogram and Functional Magnetic Resonance Imaging for Clinical Review in Epilepsy

Simultaneous electroencephalogram and functional magnetic resonance imaging (EEG-fMRI) is a unique combined technique that provides synergy in the understanding and localization of seizure onset in epilepsy. However, reported experimental protocols for EEG-fMRI recordings fail to address details about conducting such procedures on epilepsy patients. In addition, these protocols are limited solely to research settings. To fill the gap between patient monitoring in an epilepsy monitoring unit (EMU) and conducting research with an epilepsy patient, we introduce a unique EEG-fMRI recording protocol of epilepsy during the interictal period. The use of an MR conditional electrode set, which can also be used in the EMU for a simultaneous scalp EEG and video recording, allows an easy transition of EEG recordings from the EMU to the scanning room for concurrent EEG-fMRI recordings. Details on the recording procedures using this specific MR conditional electrode set are provided. In addition, the study explains step-by-step EEG processing procedures to remove the imaging artifacts, which can then be used for clinical review. This experimental protocol promotes an amendment to the conventional EEG-fMRI recording for enhanced applicability in both clinical (i.e., EMU) and research settings. Furthermore, this protocol provides the potential to expand this modality to postictal EEG-fMRI recordings in the clinical setting.

This article details simultaneous electroencephalogram and functional magnetic resonance imaging (EEG-fMRI) recording procedures that can be used in both clinical and research settings. EEG processing procedures to remove imaging artifacts for clinical review are also included. This study focuses on the example of epilepsy during the interictal period.

Simultaneous electroencephalogram and functional magnetic resonance imaging (EEG-fMRI) is a unique combined technique that provides synergy in the ...

Bioengineering

Integrating MEG and HD-EEG in Pediatric Epilepsy Localization

Electromagnetic Source Imaging in Presurgical Evaluation of Children with Drug-Resistant Epilepsy

For children with drug-resistant epilepsy (DRE), seizure freedom relies on the delineation and resection (or ablation/disconnection) of the epileptogenic zone (EZ) while preserving the eloquent brain areas. The development of a reliable and noninvasive localization method that provides clinically useful information for the localization of the EZ is, therefore, crucial to achieving successful surgical outcomes. Electric and magnetic source imaging (ESI and MSI) have been increasingly utilized in the presurgical evaluation of these patients showing promising findings in the delineation of epileptogenic as well as eloquent brain areas. Moreover, the combination of ESI and MSI into a single solution, namely electromagnetic source imaging (EMSI), performed on simultaneous high-density electroencephalography (HD-EEG) and magnetoencephalography (MEG) recordings has shown higher source localization accuracy than either modality alone. Despite these encouraging findings, such techniques are performed in only a few tertiary epilepsy centers, are rarely recorded simultaneously, and are underutilized in pediatric cohorts. This study illustrates the experimental setup for recording simultaneous MEG and HD-EEG data as well as the methodological framework for analyzing these data aiming to localize the irritative zone, the seizure onset zone, and eloquent brain areas in children with DRE. More specifically, the experimental setups are presented for (i) recording and localizing interictal and ictal epileptiform activity during sleep and (ii) recording visual-, motor-, auditory-, and somatosensory-evoked responses and mapping relevant eloquent brain areas (i.e., visual, motor, auditory, and somatosensory) during visuomotor task, as well as auditory and somatosensory stimulations. Detailed steps of the data analysis pipeline are further presented for performing EMSI as well as individual ESI and MSI using equivalent current dipole (ECD) and dynamic statistical parametric mapping (dSPM).

Author Spotlight: Advancing Pediatric Epilepsy Surgery in Children Through Novel Biomarkers and Enhanced Localization

Magnetoencephalography (MEG) and high-density electroencephalography (HD-EEG) are rarely recorded simultaneously, although they yield confirmatory and complementary information. Here, we illustrate the experimental setup for recording simultaneous MEG and HD-EEG and the methodology for analyzing these data aiming to localize epileptogenic and eloquent brain areas in children with drug-resistant epilepsy.

For children with drug-resistant epilepsy (DRE), seizure freedom relies on the delineation and resection (or ablation/disconnection) of the epileptogenic ...

Electroencephalographic Recording of Epileptic Seizures in Epilepsy-Induced Rats

Source: Soukupov&#225;, M., et al. <a href="https://app-jove-com.bdigitaluss.remotexs.co/v/58455">Microdialysis of Excitatory Amino Acids During EEG Recordings in Freely Moving Rats.</a> J. Vis. Exp. (2018)
This video demonstrates electroencephalographic (EEG) recording of epileptic seizures in epilepsy-induced rats. A rat with electrodes implanted in the ventral hippocampus is connected to the EEG recording system and placed in a plexiglass chamber. The rat is allowed to move freely while the brain activity is recorded to monitor the occurrence of seizures.

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. ...

JoVE Encyclopedia of Experiments

Neurophysiology

Stimulation and Modulation Techniques

Implanting an On-Head Electrode System in a Rat Model for Real-Time Seizure Detection

Source: Koz&#225;k, G., et al. <a href="https://app-jove-com.bdigitaluss.remotexs.co/v/56669">Chronic Transcranial Electrical Stimulation and Intracortical Recording in Rats.</a> J. Vis. Exp. (2018).
This video demonstrates the method of implanting an on-head electrode system in an anesthetized rat for real-time seizure detection. The procedure includes placing stimulation and recording electrodes, securing them with dental cement, and connecting them to a head-mounted amplifier.