The overall goal of this procedure is to measure somatosensory processing of light touch in young children. This is accomplished by first setting up event related potential methodology and an a tactile delivery system. The second step is to place an EEG net onto the child in order to measure neural activation in the brain.
Next, the stimulus control application programmed with an UFF versus sham paradigm is run. The final step is to process the data acquired from the event related potential trials. Ultimately, by comparing the response to real tactile stimuli and to the sham, one can show cortical activation in response to light touch.
So the main advantage of this method compared to some other methods like MRI or electrical nerve stimulation, is that it's very child friendly. It's fast, it's painless, and it does not require active participation, which allows us to do it both in infants and in young children. To program the stimulus control application for this protocol, first set up two serial commands.
One command should identify the puff, the other, the sham, have the stimulus control application, send the commands to a microcontroller, have the microcontroller generate a 20 millisecond duration, TTL pulse to the corresponding digital output channel. This output should be split into two lines. One for the digital input to the EEG recording system and one to the solenoid gated air valves.
Mark the opening of both valves in the EEG data stream. Measure the latency from the pulse to the puff for both real and sham conditions with an oscilloscope and a microphone. These could be uniform.
And in the order of 10 to 15 milliseconds, adjust in post recording processing. To modify the control application for the multisensory protocol, send two serial commands identifying a real puff or sham to the microcontroller, as well as a recorded speech sound or silence. Present the auditory stimuli through a speaker placed at midline above or in front of the subject.
Align the sound onset timing to be simultaneous with the onset of the puff or with the puff latency that was measured. To begin, place the electrode net on the subject's head. Adjust sensors for full contact using warm saline solution.
If on a child, ensure the child is sitting comfortably in a parent's or caregiver's lap. If on an infant, ensure that the infant is lightly swaddled and either held in a caregiver's arms or in a supine position in an open crib. Next position, a one millimeter nozzle, 0.5 centimeters below the tip of the index finger of the hand to be tested.
Place a young child's finger in a mold holder and secure with Velcro tape proximal and distal to the joint to ensure consistent distance from the nozzle. If working with an infant, place the whole palm of the hand in the holder and secure in place for enhancement of attention in young children, which results in larger specific ERP peaks in recording. Provide a task during the experiment.
For example, for five-year-olds, describe the air puffs as bubbles blown by a fish in a fish tank, a decorated box concealing the puffer apparatus can be used. Ask the child to guess whether each bubble is delivered by a blue or a red fish. Tell the child that they should remain silent and not say anything while they're performing this task.
Start the air compressor at 40 PSI through a regulator to supply valve inputs for the tactile stimuli. Then run the stimulus delivery program for the tested hand present, 60 randomly interspersed puff stimuli with 60 sham trials. The sham trials should be an air puff delivered via a separate nozzle pointed away from the finger.
Do not present more than two repetitions of a puff or sham in a row. Vary the inter trial intervals randomly between 2000 and 2, 500 milliseconds. If studying asymmetrical somatosensory disorder, also run the identical protocol for the other hand.
When running this protocol for an infant subject, note that attention to the stimulus is not required. Run the stimulus delivery as described without any task applying puff stimuli and sham trials to the palm to run the multisensory assessment. This protocol can also be combined with auditory stimuli.
Example stimuli that can be utilized are seen here. Note that GA is an example of a computer generated sound in an accent neutral female voice ga. We will demonstrate here with the five-year-old child run the stimulus delivery program.
Following through the protocol as previously described. For the tested hand, an auditory tactile paradigm should present the four stimuli seen here randomly with 60 trials per stimulus. Next, run the identical protocol over for the other hand, again, provide the child with a soundless age appropriate cartoon at the initiation of the protocol and play this throughout the procedure.
During data acquisition, choose filters and reference settings to sample data based on standard event related potential methodologies. To segment the data, filter the recorded data with desired filters and segmenting. Also be sure to perform quality control of the data.
Screen each segment for motor and ocular artifacts such as high frequency muscle activity using computer algorithms included in the ERP software. Follow this screen for a manual review, also correct data for contaminated trials using an ocular artifact correction tool. Next, average the event related potentials.
Next, re-reference them to an average reference and then perform baseline correction. Then extract the mean amplitude and peak latencies for various peaks. Extrapolated from grand average wave forms of predefined populations.
Finally include only data from electrodes overlapping the preset locations for analysis, derive data for individual electrodes and average within each cluster. Here we can see a comparison of responses to puff and sham control. In the contralateral cortical side to stimulation of an affected hand tracings represent averages of children in central parietal locations only.
The black line represents the puff. While the gray line represents a sham response. This graph shows responses recorded in the somatosensory area of the hemisphere, contralateral to tactile and binaural auditory stimuli.
Tracings represent averages of 10 children in central parietal locations only. The gray line represents the calculated summed response of ga sham plus puff. The black line represents a true multisensory response of simultaneous ga puff.
So this method can help us answer some key questions in the fields of disabilities, such as how infants and children who have various developmental disabilities process, hearing touch, and the two combined while attempting this procedure. It's essential to maintain a consistent distance from the fingertip or the hand to the nozzle tip, which is why we use mold holders or various positioners.
