The overall goal of this procedure is to estimate the dynamics of neuronal oscillations in infant brain structures over a short timescale. This is accomplished by first applying a high density sensor net to the infant's head and recording brainwaves during stimulus presentation. The second step is to pre-process the brainwave data to create event related potentials.
Next, perform a discreet multiple source analysis projected onto an age appropriate infant MRI template. The final step is application of the source montage and decomposition of the signal into the time frequency domain. Ultimately, analysis of infant brain oscillations is used to show changes in brain function in early development.
The main advantage of this technique over conventional ERP analysis is that it allows examination of brain oscillations with distinct parameters of frequency, occurrence amplitude, and time span. Visual demonstration of this technique is critical as the net application steps are difficult to learn because the actions of the hands, body, and arms in relation to the infant and the caregiver are hard to describe in words. Demonstrating this procedure will be Theresa Alpe, who's our head, EEG technician, and assisting her will be Jess, another EEG person in the lab.
To begin escort the infant and caregiver into the testing chamber, sit the infant on the caregiver's lab and have an assistant play with the infant. While the net application procedure is explained. Measure the infant's head circumference at the widest point of the head and choose the appropriate net size based on this measurement.
Next, measure nasion to nian and mark the scalp at half of the total measurement. Then do the same for the measurement from ear to ear. The final vertex between these two measurements is the cz place the net on the infant's head as the assistant holds the net connector and gathered wires behind the child.
Adjust the net position by placing the CZ electrode at the vertex scalp mark. Position each electrode by moving from back to front to ensure there is a right angle between each electrode and the head surface. Finally, plug in the net connector.
Measure the electrode impedance with a threshold of less than 50 kilo ohms. Prior to starting the recording, provide the caregiver with headphones to avoid any caregiver interference with the infant recording. Once mastered, this technique can be done in 10 minutes if performed properly.
Now that the infant is prepped for the instrument, begin by presenting the auditory stimuli through speakers that are equidistant from the infant's head. Then start the EEG recording. Provide a calm, quiet environment for the infant.
During the recording, engage the infant using quiet toys. After the experiment is completed, remove the net and dry the infant's hair and head. Begin processing the ERP data by visually inspecting the raw output.
Reject any segments with high amplitude artifact. Take the average epics for each individual and each condition. Combine these averages according to group and condition to make a grand average.
Next, coregister each individual and grand average ERP file with an age appropriate magnetic resonance template. Then estimate the number and location of underlying sources to be fitted to the data. For this auditory paradigm, use a left and right dipole with free location and rotation to process the source localization data.
Begin by choosing a time window of interest within the grand average ERP file that corresponds to a peak. Check the goodness of fit for the dipole model solution. Using the software output of residual variance, adjust the time window to minimize the residual variance.
Finally, to analyze the time frequency data in source space, apply the DPO model solution to the raw unfiltered continuous EEG data finish by transforming the time domain single trial source signal into the time frequency domain. The results from this EEG study show a representative grand average ERP response from 23 4 month old infants for control and rapid rate condition. An oddball paradigm is used to determine if an infant's brain can recognize the difference between two different tones.
Here, the results of the source localized data are shown for the left and right dipole. During the rapid rate condition, a large peak at 400 milliseconds is noticeable in the right hemisphere for the variant tone pair. In addition, these temporal spectral plots indicate the tones in the control condition with the 300 millisecond inter stimulus interval elicit event related oscillations with power changes in the delta theta range.
Following this procedure, other methods such as cross frequency phase coupling or oscillatory coherence can be performed in order to answer additional questions about early brain development. After watching this video, you should have a good understanding of how to record and analyze infant brain responses in both the time and time frequency domains.
