Caveats in Interpreting Electrophysiologic Data in Substance Abuse Research

The usefulness of any measure of neurophysiologic activity depends on the reliability, validity, and specificity of the test procedure. The issue of reliability is related to whether the spontaneous changes over time are greater than the observed drug-induced changes. For a method to have clinical value, the variability observed between testing conditions or subjects needs to be smaller than during experimental conditions. Both EEG and ERP measures have good reliability when the testing conditions are kept constant. This is extremely important because several factors including time of day (Geisler and Polich, 1990), season of the year (Polich and Geisler, 1991), recency of food intake (Geisler and Polich, 1990; 1992), and age (Goodin et al., 1978), have been shown to affect certain electrophysiologic parameters. Therefore, even though EEG and ERP measures can provide insight into the effects of drugs of abuse on the brain, their clinical value depends on how well extraneous variability is controlled. One way in which to decrease variability is to use within-subject comparisons whenever possible. In cases when it is not feasible to test the same subject under different conditions or maintain the experimental environment constant between test sessions, it is extremely important to consider the potential influence of confounding variables when interpreting the results and control for these variables statistically.

A second issue that determines the usefulness of electrophysiological measures in substance abuse research is that of external validity. External validity is related to how the impairments observed with a specific method correlate with impairments observed with other measures that test similar neurophysiological or cognitive functions. Even though both EEG and ERPs have good external validity, the clinical utility of the findings obtained with these methods is always enhanced when combined with other measures. Therefore, incorporating the use of measures like neuropsychological tests, physiological recordings and behavioral responses is strongly recommended.

Perhaps the most important aspect regarding the usefulness of EEG and ERP measures in substance abuse research is the issue of specificity. Namely, whether the electrophysiological changes observed are unique to the specific drug or condition tested. Most of the data available to date suggests that EEG and ERP measures have limited diagnostic specificity. For instance, acute administration of either ethanol, cocaine or marihuana all result in significant increases in alpha activity (Lukas et al., 1986, 1990, 1991, 1995), these increases are not only indistinguishable from each other but are also similar to those observed during transcendental meditation (Lindsley, 1952; Brown, 1970; Wallace, 1970). Given the association between alpha activity and pleasurable states, these findings suggest that the drug-induced increases in alpha activity represent a neurophysiologic response associated with reinforcement in general. Even though electrophysiological measures are not always specific enough to discriminate drug effects, this finding has allowed for subtle similarities among drugs of different classes to be identified.

Similarly, even though the reductions in P300 amplitude observed during withdrawal from either heroin, cocaine or ethanol (Poijesz et al., 1987; Kouri et al., 1996; Bauer, 1997; Noldy and Carlen, 1997) are very similar to those observed in a number of psychiatric disorders including dementia (Pfefferbaum et al., 1984) schizophrenia (Roth et al., 1980), depression (Diner et al., 1985) and borderline personality disorder (Kutcher et al., 1987), this lack of diagnostic specificity of the P300 has provided important information on the similarities between acute withdrawal from drugs of abuse and these other psychiatric disorders.

In summary, EEG and ERP measures have high reliability and validity when the experimental conditions (e.g., task demands, patient samples, recording techniques) are kept constant. Even though the diagnostic specificity of these measures is limited, when the findings are interpreted in the context of the specific drug-induced behavioral states being investigated, they can provide important information on the neurophysiological similarities between these and other psychiatric states.

Drug Free Life

Drug Free Life

How To Beat Drugs And Be On Your Way To Full Recovery. In this book, you will learn all about: Background Info On Drugs, Psychological Treatments Statistics, Rehab, Hypnosis and Much MORE.

Get My Free Ebook

Post a comment