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Of particular importance is the study of the actions of drugs in this respect.

Although no drugs act exclusively on the hypothalamus or a part of it, there is sufficient specificity to distinguish drugs which shift the hypothalamic balance to the sympathetic side from those which produce a parasympathetic dominance.

The former comprise analeptic and psychoactive drugs, the latter the tranquilizers.

Specific differences exist in the action of different drugs belonging to the same group as, for instance, between reserpine and chlorpromazine.

Important as these differences are, they should not obscure the basic fact that by shifting the hypothalamic balance sufficiently to the parasympathetic side, we produce depressions, whereas a shift in the opposite direction causes excitatory effects and, eventually, maniclike changes.

The emotional states produced by drugs influence the cortical potentials in a characteristic manner ; ;

synchrony prevails in the EEG of the experimental animal after administration of tranquilizers, but asynchrony after application of analeptic and psychoactive drugs.