Expression of behaviour and psychoactive Drugs in the Rat EEG

Brain activity and behaviour are related to each other. Psychoactive drugs can influence both brain activity and behaviour. In order to be able to understand the interplay between brain activity as measured by the electroencephalogram (EEG), behaviour, and psychoactive drugs, it is not sufficient to describe changes in either behaviour or EEG separately. Rather, changes in EEG caused by psychoactive drugs should be described in direct concurrent relation with the subject's ongoing behaviour. Thus, this thesis was aimed at the description of how spontaneous and pharmacologically induced activity is represented in EEG activity and how behavioural activity is determined by spontaneous and pharmaco-EEG activity in rats. In this thesis the strong relationship between behaviour and EEG in rats is confirmed. Furthermore, it was found that spontaneous behavioural activity levels are reflected in the representation of behaviour in the EEG. Also, psychoactive drugs can influence the representation of behaviour in the EEG, as some pharmaco-EEG effects occur specifically during certain behavioural elements. Thus, the relationship between EEG and behaviour is not completely fixed but can be modulated by spontaneous and pharmacological factors. Furthermore, these two factors interact, as psychoactive drugs influence the modulating effect of behavioural transitions on the relationship between EEG and behaviour. Although modulation takes place, a dissociation of the relation between EEG and behaviour by the GABAA modulators diazepam and zolpidem, as suggested in the literature, was not found. The modulation of the relationship between EEG and behaviour, spontaneously or pharmacologically, is hypothesised to determine fluctuating probability levels for behavioural activity to occur by influencing (sensorimotor) information processin