Behavior
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An Electrophysiology Protocol to Measure Reward Anticipation and Processing in Children
Chapters
Summary October 4th, 2018
This protocol is designed to measure reward anticipation and processing in young children with and without autism. Specifically, the protocol is designed to study the neural correlates of reward during social and nonsocial conditions while controlling for reward between conditions.
Transcript
This method can help answer key questions about social motivation and the reward system in autism. Such as, are children with autism less rewarded by social images compared to their typically developing peers? The main advantage of this technique is that physical stimulus properties are controlled between conditions and the reward itself is the same between conditions.
These are important experimental controls. Helping me with the protocol today will be my PhD student, Laura Alba. Begin by creating two blocks of stimuli in an EEG presentation software package.
One social block and the other non-social. Set up each trial to contain the following:A fixation cross, two boxes with question marks, an arrow pointing to the box the participant chooses via the button press, and a feedback stimulus. Lastly, once the stimuli have been created, ensure that a button box will be available to provide to the participant during the experimental trial.
Begin by escorting the participant into a testing room. Administer cognitive tests to the participant to confirm that the child has a cognitive score within the low average to average range. Next, if the participant is eligible for the study, escort them into the testing room.
Adjust the chair so the participant is 72 centimeters away from the computer screen. Measure the participant's head to determine which size cap is appropriate for the head size. Next, select an EEG cap with 32 silver/silver chloride electrodes in the international 10-20 system, and fit the EEG cap to the participant's head such that the CZ electrode is placed at the middle of the scalp, as per the 10-20 system.
Then inject conductive gel into the electrodes. Connect the EEG cap to the amplifier with a low pass filter at 70 hertz, a directly coupled high pass filter, a 60 hertz notch filter, and a 500 hertz sampling rate. Then use a blunted needle or sterile wooden stick to swirl inside the electrode to move any hair and allow the gel to contact the scalp.
Use an impedance meter to ensure that impedance is below 10 kiloohms for a low impedance system and below 50 kiloohms for a high impedance system. After all the electrodes on the cap show acceptable impedance levels, place horizontal, or HEOG, eye movement electrodes at the canthus of each eye, and place the vertical, or VEOG, electrodes above and below the eye. Next, ensure that the participant understands the instructions for the task and how to use the button box.
Check that the EEG computer is recording and then begin the experimental blocks. Provide brief, 30 second breaks, after every 15 trials to allow the participant to move around, if needed. After each block, have the participant fill out a Likert scale about how much they enjoyed the guessing game and how often they felt they could get correct answers.
Once the experiment is complete, take off the EEG cap and allow the participant to wash and dry their hair. Finally, clean and sterilize the EEG cap for the next participant. These results suggest that typically developing, or TD children, anticipate reward stimuli accompanied by faces more robustly than children with ASD.
While TD children anticipate face stimuli significantly more than non-face stimuli, children with ASD do not evidently show significant differences in brain activity between conditions. While attempting this procedure, it's important to remember to check that the participant fully understands the directions and how the game works. Following this procedure, other methods, for example, eye tracking or FMRI, could be simultaneously performed in order to answer additional questions like, where are children with and without autism looking during this type of task or, what areas of the brain are activated in children with and without autism during this task?
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