Electrophysiological models for the study of cognition enhancers.

Electrophysiological approaches range from global EEG studies to single unit recordings. Quantified EEG studies indicate that cognition enhancers increase the power of fast-frequency (beta) EEG activity in humans and the duration of hippocampal theta in animals. A problem here is the distinction between improved cognition and increases in general arousal, although the two might have the same end effect. A second global approach is the use of the evoked potential or even the conditioned evoked potential, for example the P 300 wave. This approach, using defined brain circuits, would appear to be more specific than global EEG models. Both approaches can be used in parallel studies in animals and man. Studies at more cellular levels can only be used in animals and suffer from severe constraints. The most precise approach, single cell recording, cannot be conducted in freely behaving animals, whereas multi-unit approaches in awake animals tend to produce many artefacts. However, techniques using microintophoretically applied drugs in freely moving rodents and monkeys can contribute to the understanding of mechanisms of action. In vitro studies, for example long-term potentiation in hippocampal slices, may represent a neuronal model of learning but its role in normal brain function has still not been elucidated.