Electroencephalography (EEG), the recording of electrical signals from the brain, provides a noninvasive measure of brain function as it is happening. Research using EEG, as well as event-related potentials (ERPs) and event-related oscillations (EROs), which measure brain activity in response to a specific stimulus, have shown that the brain activity of alcoholics and nonalcoholics differs in some characteristic ways. These differences are consistent with an imbalance between excitation and inhibition processes in the brains of alcoholics. KEY WORDS: AOD (alcohol and other drug) dependence; electroencephalography; electrical life processes; evoked potential; P3 amplitude; brain wave; brain imaging; excitatory neurotransmitters; hyperexcitability; disinhibition; neurobiological theory of AODU (alcohol and other drug use); AOD use susceptibility
Researchers studying the effects of alcohol use on the brain are aided by techniques that yield images of the brain's structure and reveal the brain's activity as it is happening. Tools that produce images of the brain's structure, such as magnetic resonance imaging (MRI) and positron emission tomography (PET), are described in other articles in this issue. This article examines the techniques of electrophysiological brain mapping, which best reveals brain activity as it occurs in time, in fractions of seconds.
Electroencephalography (EEG) is the recording ("graph") of electrical signals ("electro") from the brain ("encephalo"). (The resulting report, called an electroencephalogram, also is abbreviated EEG.) Each nerve cell (i.e., neuron) in the brain produces a tiny electrical charge; when a number of neurons become active, the sum of these tiny electrical charges can be detected on the surface of the scalp. Small electrodes placed on the scalp detect this electrical activity, which is magnified and recorded as brain waves (i.e., neural oscillations). These brain waves illustrate the activity as it is taking place in various areas inside the brain.
In the purely resting state, brain waves often are randomly active. However, when a person perceives or responds to a sensory or cognitive stimulus (e.g., a blue triangle), groups of neurons fire together, and the EEG is no longer random. The activity that is related to processing of the stimulus always occurs at the same time after the stimulus (i.e., is time-locked). This time-locked (i.e., event-related or evoked) activity is embedded in background random EEG that is not related to the stimulus processing. In order to see the tiny event-related activity, the EEG is averaged across multiple identical occurrences or trials (e.g., whenever the blue triangle occurs in a series of red squares); activity that is random with respect to the stimulus cancels out with each presentation of the stimulus, whereas the time-locked activity that occurs at the same time on every trial increases in the average. The waveform produced after averaging across identical trials is called an event-related potential (ERP). If one were to make a movie of the brain activity involved in the mental processing of a stimulus as it happens in real time, one would first see early fast activity that is related to sensory reception (e.g., seeing a visual stimulus) occurring in the visual cortex (occipital lobe [see figure 1]); this would then be followed by slower activity related to higher cognitive function (e.g., identification and attention to a blue triangle in a series of squares), which involves activity in the parietal and frontal lobes (figure 1). The fast and slow neural oscillations that underlie the ERP, called event-related oscillations (EROs), represent sensory and cognitive functions.
This article reviews research indicating that alcoholics manifest aberrant resting EEGs, ERPs, and EROs, and discusses the significance of these findings.
THE RESTING ELECTROENCEPHALOGRAM
The resting EEG is the recording of ongoing spontaneous brain electrical activity while the person being examined is relaxing (the person's eyes may be open or closed). …