From event-related potential to oscillations: genetic diathesis in brain (dys)function and alcohol dependence.

KEY WORDS: Alcoholism; alcohol disorders; children of alcoholics; alcohol-related genetic factors; risk factors; genetic markers; brain function; brain wave; brain activity diagnosis; neuroimaging; electroencephalography (EEG); event-related potential (ERP); P3 amplitude; event-related oscillation (ERO) Recording the brain's electrical activity using electrodes placed on the individual's scalp provides noninvasive sensitive measures of brain function in humans. Regardless of whether an individual receives sensory information or performs higher cognitive processes, the brain regions involved exhibit measurable electrical activity, and by recording this activity with numerous electrodes placed on different areas of the scalp, researchers can determine when and where in the brain information processing occurs. Two general approaches can be used to record these neuroelectric phenomena: * The continuous electroencephalogram (EEG) records brain activity when the subject is at rest and not involved in a task. It reflects the sum of the random activity of thousands of neurons that have similar spatial orientation in the brain. This activity typically fluctuates in wave-like patterns, and depending on the frequency of these patterns, one distinguishes different brain waves called a (frequency of 1 to 3 Hz), e (frequency of 4 to 7 Hz), a (frequency of 8 to 12 Hz), â (frequency of 12 to 28 Hz), and a (frequency of 28+ Hz) rhythms. Variations in the patterns of these brain waves can indicate the level of consciousness, psychological state, or presence of neurological disorders. * Event-related potentials (ERPs) are recorded while the subject is performing a sensory or cognitive task. They reflect the summated activity of network ensembles active during the task and are characterized by a specific pattern called the waveform, which is composed of negative and positive deflections (i.e., waves). For example, a target stimulus detected amidst a series of other nontarget stimuli produces a positive wave around 300 milliseconds after the stimulus. This is known as the P300 or P3 response. The main advantage of these techniques is that they provide millisecond-by-millisecond indices of brain function and therefore provide excellent temporal resolution. However, because these measurements typically record the activity of thousands of neurons spread out over a certain area, they provide less spatial resolution than many neuroimaging methods (e.g., magnetic resonance imaging). In recent years a third type of electrophysiological response, event-related oscillations (EROs) have been identified that may serve as a measure of cognitive functions and which, as described in this article, may serve as markers for alcoholism risk. EVENT-RELATED OSCILLATIONS: A MEASURE OF COGNITIVE FUNCTIONS Until recently, ERPs were the basic electrophysiological indices of cognition that provided valuable insights into human brain processes. Substantial literature now indicates that some ERP features may arise from changes in the dynamics of ongoing EEG rhythms/oscillations of different frequency bands that reflect ongoing sensory and/or cognitive processes (Basar 1999; Basar et al. 1999; Buzsaki 2006). In other words, the EEG oscillations that are measured in a resting state become organized, amplified, and/or coupled during mental activity, or the network activity induced by an event or stimulus may trigger specific oscillatory responses, thus giving rise to an "evoked" (strongly locked to the stimulus/event) or "induced" (weakly associated with to the stimulus/event) rhythmicity (Basar 1980; Basar 1999; Makeig et al. 2002). These EROs can influence the timing of neural activity and coordinate synchronous activity in groups of active neurons (Fries 2005). Thus, EROs represent a basic mechanism of neural communication, providing links to associative and integrative brain functions. High-frequency (i.e., â, a) EROs are implicated in short range communication, whereas low frequencies (i. …