Alcoholism and the brain: an overview

Alcohol Research & Health, Spring, 2003 by Marlene Oscar-Berman, Ksenija Marinkovic

Imaging of Brain Function: Electromagnetic Methods. In spite of their excellent spatial resolution--that is, the ability to show precisely where the activation changes are occurring in the brain--hemodynamic methods such as PET, SPECT, and fMRI have limitations in showing the time sequence of these changes. Activation maps can reveal brain areas involved in a particular task, but they cannot show exactly when these areas made their respective contributions. This is because they measure hemodynamic changes (blood flow and oxygenation), indicating the neuronal activation only indirectly and with a lag of more than a second. Yet, it is important to understand the order and timing of thoughts, feelings, and behaviors, as well as the contributions of different brain areas.

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The only methods capable of online detection of the electrical currents in neuronal activity are electromagnetic methods such electroencephalography (EEG), event-related brain potentials (ERP), (4) and magnetoencephalography (MEG). EEG reflects electrical activity measured by small electrodes attached to the scalp. Event-related potentials are obtained by averaging EEG voltage changes that are time-locked to the presentation of a stimulus such as a tone, image, or word. MEG uses sensors in a machine that resembles a large hair dryer to measure magnetic fields generated by brain electrical activity. These techniques are harmless and give us insight into the dynamic moment-to-moment changes in electrical activity of the brain. They show when the critical changes are occurring, but their spatial resolution is ambiguous and limited.

ERP and MEG have confirmed that alcohol exerts deleterious effects on multiple levels of the nervous system. These effects include impairment of the lower-level brain stem functions resulting in behavioral symptoms such as dizziness, involuntary eye movement (i.e., nystagmus), and insecure gait, as well as impairment of higher order functioning such as problem solving, memory, and emotion. ERP and MEG are remarkably sensitive to many alcohol-related phenomena and can detect changes in the brain that are associated with alcoholism, withdrawal, and abstinence. That is, these methods show different activity patterns between healthy and alcohol-dependent individuals, those in withdrawal, and those with a positive family history of alcoholism. As shown in figure 3, when brain electrical activity is measured in response to target stimuli (which require the subject to respond in some way) and nontarget stimuli (to be ignored by the subject), the brains of alcoholics are less responsive than the brains of nonalcoholic control subjects. Some of the ERP abnormalities observed in alcoholics do not change with abstinence, and similar abnormalities have been reported in patients who do not drink but come from families with a history of alcoholism. The possibility that such abnormalities may be genetic markers for the predisposition for alcoholism is under intensive scrutiny in studies combining genetic and electromagnetic measures in people with or without a family history of alcoholism (Porjesz and Begleiter 1998).