Behavior
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Event-related Potentials During Target-response Tasks to Study Cognitive Processes of Upper Limb Use in Children with Unilateral Cerebral Palsy
Chapters
Summary January 11th, 2016
Several children with unilateral Cerebral Palsy seem to disregard the preserved capacity of their affected upper limb. This Developmental Disregard is extensively described in the literature but the involved cognitive processes have not been studied. To study underlying cognitive factors of upper limb control, an event-related potential protocol was developed.
Transcript
The overall goal of this procedure is to assess cognitive aspects underlying upper limb control in children with movement disabilities. This is accomplished by studying event-related brain potentials during simple, manual target response tasks. This method can help answer key questions related to the underlying cognitive processes that might contribute to specific movement restrictions in children with movement disabilities.
The implications of this technique extends toward therapy in children with cerebral palsy, because it allows us to unravel different cognitive factors that also contribute to the individual movement restrictions. Visual demonstration of this method is critical, as child-friendly EEG recordings and adaptive, event-related potential protocols suitable for children with movement restrictions are difficult to learn. Begin by choosing visual stimuli that are easy to distinguish based on color or shape.
Use simple graphic designs, like smiley faces, that will keep the child's attention on the task, and ensure that they are big enough on the screen to be easily recognized by a child. Present the stimuli to the left or right side of the screen, to respectively induce left or right-hand movements. Include a background stimulus to the other side of the screen to control for stimulus lateralization.
To register responses to the stimuli, provide the child with two big response buttons with very low response force requirements, to ensure that children are easily able to respond. Use response devices that can register time-accurate button presses and deliver related stimulus markers to the EEG computer. Finally, when a stimulus is presented on the computer screen, use a stimulus delivery and experimental control program that is time-accurate, to send time-locked markers to the data acquisition protocol.
Begin by distracting the child with a film to watch during EEG setup. In order to conduct the study in a familiar environment for the child, set up a mobile EEG lab in which two computers are used;one to present the stimuli, and the other to record and digitalize the EEG. Begin the electrode setup by cleaning the skin at the position of the reference electrodes on the left and right mastoid bones, in order to reduce the impedance.
Gently apply scrub cream to remove dead skin cells, and then clean it with alcohol to remove oily substances. Measure the head circumference by placing a measuring tape around the widest part of the head to determine the cap size. Then, apply the cap of the correct size onto the head.
Ensure the cap is in the right position by measuring the distance between the inion and the nasion, and then between the left and right interoral indentions. Place the CZ electrode at the halfway point between these two measurements. Next, organize the electrodes on the head according to the international 10-20 system by using the numbers on the cap and electrodes.
Locate electrodes at five midline sites and 24 lateral sites, to find spacial maxima of the event related potential components. Place one more electrode on the right mastoid bone for linked-reference recording, and place the ground electrode on AFZ. Following that, use a blunt needle to fill the electrodes with conductive gel in order to maximize skin contact.
Gently abrade the skin under the electrode to lower the impedance levels, and be careful not to apply too much gel, as the signal may get distorted. Keep the electrode impedance below 20 kilohms, by using an impedance meter when attaching the electrodes. Next, clean the skin surrounding the eyes for the electrooculogram, or EOG, electrodes.
Place EOG electrodes around the eyes to coregister an EOG to correct the EEG signal for eye movements. For children, only place two EOG electrodes:one below the right eye, and the other on the outer canthus of the right eye. Finally, use FP2 and F7 as reference electrodes for the EOG recording, when applying an ocular correction during offline data processing.
Begin by placing the computer screen 40 centimeters in front of the child. Locate the two red buttons next to the keyboard, one on the right, and the other on the left side. Keep the distance between the buttons at 30 centimeters, to avoid the possibility that the wrong hand is used to press the button.
Place the child's hands slightly above the two red buttons with elbows resting on the table. Instruct the child to respond as quickly as possible to the target stimuli, by pressing the red button on the side that the target stimulus is presented. If no-go stimuli are included, instruct the child to inhibit their response whenever a no-go stimulus is presented.
Finally, before starting the experiment, conduct a short trial session lasting no longer than one minute, to prevent inducing fatigue later on in the experiment. Ensure that all stimuli that are used in the experiment appear at least once during this trial session. This protocol uses event related brain potentials to study the underlying cognitive factors of upper limb control in children with unilateral cerebral palsy.
Here, typical reaction time data of children with unilateral cerebral palsy are shown, indicating differences between the less affected and affected hand, in which the affected hand is slower to respond after the target stimulus is presented. Here, separate ERP wave forms are shown, following target stimulus presentation preceding a manual response of the less affected side and the affected side. By comparing these ERP wave forms between different groups or conditions, differences in underlying cognitive factors of upper limb control can be revealed.
After watching this video, you should have a good understanding of how to record and analyze event related brain potentials that are related to cognitive processes underlying upper limb control in children with movement disabilities. Once mastered, recording EEG and completing event related potential analysis can be done in a few hours if it is performed properly. While attempting this procedure, it's important to remember that the visual target response tasks should be adapted in a way that is feasible for children with movement restrictions.
By using different experimental paradigms during this event related potential procedure, different cognitive processes can be studied in order to answer additional questions. This method can help us to answer key questions related to underlying cognitive factors that might contribute to different movement restrictions in distinct movement disabilities.
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