Application of ERP Methodology

ERP methodology is ideal for use in younger populations and is well suited for assessment of neural function even in young infants; in contrast, the use of other, more invasive imaging techniques such as functional magnetic resonance imaging (fMRI) or positron emission tomography (PET) are typically only justified in infants and young children when medically necessary. In addition, although other, less invasive methods such as magnetoencephalography (MEG) could potentially be used with younger children, the typical task demands associated with the use of these imaging methods as well as the need for the participant to sit still and sustain attention for long periods of time restrict their use for young children. In contrast, ERP experiments can be designed to require little if any motor response from the participant. Also, whereas participants in ERP experiments do need to minimize motor activity during data collection, as large muscle movements will introduce movement artifact (EMG) into the data, there is no need to remain absolutely still during data collection. While it is possible to correct for a relatively small degree of head movement during an fMRI experiment, the degree of movement allowed in an ERP experiment is generally greater and more easily corrected. The need for participants to remain very still during fMRI, in addition to ethical considerations concerning the use of this technology in younger, non-clinical samples, generally precludes the use of fMRI in children under the age of 8 years. In contrast, however, ERPs can be practically utilized beginning in the neonatal period.

Although metabolic-based procedures for brain imaging such as fMRI do provide superior spatial resolution and lend themselves ideally to the localization of brain function, ERPs are still unmatched in their ability to provide millisecond-level temporal resolution of neural functioning. Historically, however, ERPs have provided very poor spatial resolution. As recently as 15 years ago, it was not uncommon for published ERP studies to have utilized as few as 3 or 4 electrodes, and up until merely 10 years ago a 32-channel electrode array was considered state of the art. However, with the recent advent of high-density EEG electrode arrays, allowing experimenters to record from 128 and even 256 electrodes simultaneously (e.g., Geodesic Sensor Net [GSN], Tucker, 1993), and the application of newly developed sophisticated source localization software algorithms to these data (e.g., Brain Electrical Source Analysis [BESA], Berg & Scherg, 1994; Scherg, 1990), it is now possible to localize the source of ERP signal to a much greater degree of accuracy and certainty than ever before. In dipole-source modeling, complex mathematical models are applied to scalp-recorded electrical activity, whereby location (source) and the relative strength of the EEG signal can be inferred across the scalp.

This ability to localize neural function fairly well with ERPs, combined with their high degree of temporal resolution, makes them an ideal tool with which to study neural functioning in infants and young children. In addition, given the relatively noninvasive procedure required to place electrodes on the scalp and record ERPs, this methodology is ideally suited for use with children who have experienced trauma and for whom enduring more invasive brain imaging procedures may exacerbate their potentially stressful reactions to participating in research of this nature. In sum, although ERPs do not represent a type of functional neuroimaging technique per se (in the strict sense that ERPs do not yield a direct "image" of the brain), the data provided by this methodology can provide an invaluable addition to knowledge about the neurofunctional characteristics of many aspects of cognition and memory.

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