Event-Related Potentials and Cognitive Function in Alcoholism.

Cognitive impairment in alcoholics(1) ranges from severe memory disorders and dementia to subtle impairment of the ability to process and interpret sensory information. A majority of alcoholics may exhibit subtle cognitive impairment. For many years, these milder deficits were not well understood because the sensitive techniques required for their detection were unavailable. Today, subtle cognitive deficits can be studied using event-related potentials (ERP), a special application of the electroencephalogram (EEG). Traditional EEG techniques use electrodes placed in standard positions on the scalp to measure the spontaneous electrical activity of the brain. Characteristic EEG patterns have been correlated with different mental and behavioral states. In contrast, ERP's are elicited in response to sensory stimuli, a such as sights or sounds. Brain electrical responses can be measured within a fraction of the second that follows exposure to a stimulus, providing an immediate record of brain activity associated with information processing. How ERP's ARE OBTAINED The brain can generate ERP's in response to stimuli in any sensory system, or channel. In most ERP experiments, subjects are exposed to stimuli in the visual or re auditory channels (or both). Visual stimuli, such as shapes or letters, can be presented on a computer screen; auditory stimuli, such as tones or clicks, can be presented through headphones. The subject may be asked to attend to some stimuli while ignoring others. Generally the subject is asked to make a behavioral response to a certain stimulus. For example, he or she may be asked to press a button whenever the stimulus is detected. Stimuli that require a response are called targets. In some tasks, the subject must attend or respond to a specific stimulus in one sensory channel while ignoring all stimuli in another sensory channel; the sensory channel containing the target stimulus is called the relevant channel. Scalp electrodes record the subject's brain electrical activity during the task. The electrical signals are processed electronically and displayed as undulating lines, each line forming a series of peaks (positive waves) and valleys (negative waves). Waves, or components,(2) are named according to their polarity-positive (P) or negative (N)--and their latency. Latency is the interval, in thousandths of a second (milliseconds msec ) between the occurrence of a stimulus and the peak of the wave. Early ERP components (those with latency less than 100 msec) are automatic responses to physical characteristics of the stimulus. In contrast, later components reflect the subject's processing of the stimulus and are influenced by the psychological circumstances under which the stimulus is presented. WHAT ERP's INDICATE ABOUT COGNITIVE PROCESSES Various mental operations are involved in responding to a target stimulus. For example, the subject must focus attention on the relevant sensory channel, ignore irrelevant stimuli, distinguish among similar stimuli and then recognize the target stimulus by matching it to a template stored in the memory. These operations are correlated with electrical activity in groups of nerve cells from the sense organs themselves (i.e., eyes, ears) to the highest centers of information processing in the brain. Researchers have identified certain ERP components that appear to reflect these operations. ERP components between experimental and control subjects are compared in terms of changes in latency and differences in wave height (i.e., amplitude). Selective Attention: N1 and Nd N1 (or N100) is a negative wave occurring approximately 100 msec after a stimulus. N1 consists of two components that may overlap in time--an earlier automatic component followed by an attention-related component. The automatic component of N1 is the same in both the relevant and irrelevant channels. In normal subjects, N1 has a greater amplitude when elicited by stimuli in a relevant sensory channel compared with the N1 elicited by stimuli in an irrelevant channel. …