Neuroscience
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Event Related Potentials (ERPs) and other EEG Based Methods for Extracting Biomarkers of Brain Dysfunction: Examples from Pediatric Attention Deficit/Hyperactivity Disorder (ADHD)
Chapters
Summary March 12th, 2020
EEG-methods are applied for extracting biomarkers of brain dysfunctions. The focus is on multi-channel event-related potentials (ERPs) recorded in a cued GO/NOGO task. Non-brain artifacts are corrected and ERPs are compared with the normative data. Examples relate to biomarkers for ADHD diagnosis and prediction of medication response.
Transcript
Comparing EEG spectra and event-related potentials, ERPS, with a database can provide important information about brain function. The advantages of these techniques are that they are noninvasive, affordable, and can relate to a large number of scientific studies. Demonstrating these techniques will be Maria Danielsen, a psychology candidate who has worked as a technician in our clinic for about two years.
To create a corresponding EEG data file, in the software click File and New. The subject's card will appear on the screen. After filling in all of the appropriate information, measure the nasion-inion distance on the head of the subject.
The center of the frontal pole electrodes should fall on a horizontal line 10%of this distance above the nasion. Apply skin prep gel to the earlobes and fill the ear electrode cups with conductive electrode gel. Attach the ear electrodes and place the cap symmetrically on the head with the frontal pole electrodes placed in the center of the frontal pole.
Pull the cap down as far as possible to secure it close to the head and place the waistband around the chest. Fasten the push buttons connected to the cap to this band to prevent the cap and electrodes from moving during testing and connect the cap cable and ear cables to the amplifier. Next, click on the WinEEG menu control of impedance icon and fill the syringe with gel.
Use the syringe to fill all of the electrode holes. The impedance is okay when the black circles are yellow. The equipment is ready when all 20 of the holes have a yellow color and the color difference between individual holes is small.
When the equipment has been properly placed, click the start button to initiate the EEG monitoring and inform the subject that the test will take about one hour. Ask the subject to relax in the comfortable chair with eyes closed and click the red circle to acquire the EEG. After clicking next, select eyes closed to start the registration.
After three minutes click pause and ask the subject to open their eyes while relaxing and looking at the screen in front of them. Then click the red circle to continue the registration. After another three minutes, click stop and save.
Before starting an EEG recording, have the subject hold a button switch in their right hand and open the task menu. Select VCPT on the secondary computer in front of the subject. Inform the subject that pictures will come in pairs with the first picture being followed by the second after one second and that after three seconds, a new pair will appear following the same pattern.
Instruct the subject to click the mouse button as quickly as possible every time the AA combination in which the two animals are identical appears. Instruct the subject to not push the mouse button on AP, PP, or AH combinations. Tell the subject to ignore the random sounds in PH combinations.
After delivering the instructions, press Enter to run the task for about two to five minutes to train the subject on the go/nogo task. At the end of the training task, select the switch to slave mode option. To start the experiment, select the EEG acquisition option from the recording menu on the main computer.
On the recording menu, select stimulus presentation program. The stimuli presentation program option will be highlighted. Select VCPT and start the stimuli presentations on the secondary computer.
When all 400 trials have been completed, push pause, stop, and save before ending the registration. To remove eye movement artifacts from the data, left-click on the time bar at the beginning of the fragment to select the EEG fragment of interest and right-click on the time bar at the end of the fragment. The whole fragment will be highlighted in yellow.
To enable comparison of the individual spectra and event-related potentials with the HBI reference database, select the independent component analysis method and select the topographies associated with eye blinks and horizontal eye movements. Then click OK to accept the selections and implement the mark artifacts procedure from the analysis menu. To calculate the EEG spectra, select eyes closed or eyes opened in the analysis menu to select the EEG spectrum and fragment of interest and click OK.Then in the analysis menu, select comparison to compare the individual spectra with the database.
To calculate the event-related potentials, select an EEG VCPT file in the common average montage and click compute ERP from the analysis menu. Click OK.A window depicting parameters of ERP computations will appear. From the four small windows above the graph labeled one, two, three, and four, select the component of interest in one window and the none option in the others.
On the right vertical menu, select the time interval of interest. To map the wave for event-related potentials, right-click at the selected time along the x-axis of any graph. Then release and select add map.
The corresponding maps will appear at the bottom of the page. To view the number of omissions, commissions, mean reaction time for a-a GO, and the real time variability, right-click in the event-related potentials window and select groups info. The a-a GO line shows the number of omission errors, reaction time and reaction time variability.
The a-p NoGO line shows the number of commission errors. Under analysis, select comparison. Then select the subject's file and the comparison file in the right window and click OK.To compare the event-related potentials with the reference database, select comparison of results from the analysis menu and select the subject's file and the HBI database.
Then right-click at the time point and channel of interest to obtain the significance level of the deviation from the reference. To select groups for evaluating the event-related potential difference, click the arrow at one. For referential event-related potentials, click two.
To see the difference, click three. For active group four, select none. To define the time interval of interest, enter the time interval from and the duration in milliseconds.
Then position the cursor at the time point and channel of interest and right-click to select add map. A map showing the deviance from the reference will be shown. Other files instead of the HBI database can be selected for comparisons.
Here, event-related potential correlates of dysfunction of proactive cognitive control in the representative ADHD group are shown. Two indices of proactive cognitive control were reduced in the ADHD group compared to a healthy control group in this analysis. In this figure, event-related potential correlates of dysfunction of reactive cognitive control in the ADHD group can be observed.
Two indices of reactive cognitive control were also reduced in the ADHD subjects compared to the healthy control group. To secure a high-quality registration, minimize the muscle and movement artifacts as much as possible. A secure connection between the task and WinEEG computer is critical.
Although these methods are part of a total clinical examination for generating hypothesis, they cannot replace methods like clinical interviews, medical examinations, neuropsychological tests or observations.
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