The relevance of the neurophysiological concepts of excitation and inhibition to clinical psychiatry.

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The discovery of the excitatory function of the brainstem reticular formation helped in the formulation of a number of psychological theories relating to arousal. The demonstration of sensory inhibition, and the discovery of inhibitory centres in the cortex, hippocampus and mid-pons provided a physiological explanation for the phenomenon of habitutation. The measurement of indices of arousal and habituation, together with careful clinical assessment, proved useful in a number of diagnostic studies. In normal subjects arousal was subjectively perceived as wakefulness and was associated with predictable changes in physiological measures. The excitation-inhibition balance, measured by the amplitude of the orienteering reflex, its rate of habituation, and habituation point, was correlated with the Neuroticism Score on the Eysenck Personality Inventory. Thought disorder schizophrenics failed in habituate, and paranoid schizophrenics had difficulty dishabituating, indicating abnormal inhibitory function. Some neurotic groups with symptoms of chronic anxiety, had an abnormally high state of arousal. Impaired habituation in cases of Korsakoff's psychosis implicates the hippocampus in the mediation of inhibition. The catecholamines have an important role in regulating excitation, as shown by the increase in arousal associated with L-Dopa administration, and the decreased arousal shown after alpha methyl dopa.