The Use of Brain Electrophysiology Techniques to Study Language: A Basic Guide for the Beginning Consumer of Electrophysiology Information

Article excerpt

Abstract. This article provides a basic background for the professional who is interested in utilizing event-related potential (ERP) approaches to study language processes but has little background in or knowledge about the technique. First, a brief history of the emergence of this technology is presented, followed by definitions, a theoretical overview, and a practical guide to conducting ERP studies. The basis for choice of electrode positions, equipment characteristics (e.g., filter settings), and analyses are also discussed. Finally, examples of language studies that utilize this information in a research study are provided.

There has been a long-standing interest by researchers and theorists in brain-behavior relations. This interest has led to the development and adaptation of instruments and methodologies that measure the brain's responses for use in studying developmental issues. Techniques such as electroencephalography (EEG), event-related potentials (ERP), and brainstem-evoked response (BSER) all share a common approach to cortical electrophysiology -- scalp electrodes are used to detect electrical activity generated by the brain. These techniques can provide insights into brain-behavior developmental issues that complement and supplement information obtained through more traditional behavioral measures.

This article reviews the history of cortical electro-physiological approaches to investigate brain-behavior relations. An overview of the procedure is provided along with rationales for various components of it. We briefly also comment on how these approaches compare to other techniques, such as Positron Emission Tomography (PET), Magnetic Resonance Imaging (MRI), and functional Magnetic Resonance Imaging (fMRI). A final section will describe the current use of ERP techniques in longitudinal research to investigate the relation between brain functioning in infancy and subsequent cognitive and language development in school-aged children, with a focus on reading and reading disability.

What Are Event-Related Potentials?

In order to understand ERPs (event-related potentials) or Eps (evoked potentials) some general background on the electroencephalography or EEG is useful. In the general EEG (electroencephalogram) technique, electrodes attached to the scalp allow physicians to measure the brain's electrical activity or EEG. The idea behind EEG is straightforward. The human body utilizes electricity in its operation, somewhat like cable cars, computers, and CD players use electricity. One major source and processing station of that electricity is the brain, or more specifically, the neurons that make up much of what we call the brain. Every time a group of neurons perform some function, they generate a small amount of electrical energy, which spreads throughout the brain to other neurons. However, a portion of this electrical signal passes through the brain and travels through the skull where it can be measured on the scalp. By positioning electrodes on the scalp's surface, EEG amplifiers magnify the minute electrical discharges (perhaps 5-10 [micro]V, or millionths of a volt) that occur. Such electrical currents on the scalp thus reflect and indicate the activity level of groups of neurons within the brain. The end result is a readout of the ongoing electrical discharges (in the form of continuous brain waves) that were produced during activity (e.g., sleeping, listening to music, reading) over some period of time.

An EEG field at the scalp can only be recorded if large numbers of neurons are active at the same time, and they must all be aligned in the same orientation. If they are not aligned, that is, they are laminar, then the positive and negative fields of differently aligned neurons tend to cancel each other out. Subcortical brain structures, such as the basal ganglia, may be highly active electrically, but do not appear to contribute to the scalp EEG because they are not aligned with cortical brain structures. …