THE NEURONAL BASIS OF COMPULSIVE BEHAVIOUR IN ANOREXIA NERVOSA

The relationship between arousal and efficiency of the brain is shown by the inverted U of the Yerkes-Dodson curve. Measuring arousal has been difficult because the three types of arousal (EEG, behaviour and autonomic) do not change in unison. From Magoun's work, arousal can be stimulated via the reticular formation or from parts of the cortex. Kyotorphin (Tyr-Arg) causes widespread excitation when applied to the cortex and may represent this mechanism: it is then inhibited only by noradrenaline. The hippocampus causes stimulation of arousal to persist after the exciting stimulus stops and can itself be stimulated into long term potentiation. The latter may be related to the onset of compulsive behaviour which appears to occur only with excessive stimulation of arousal. The opioid dynorphin is the main stimulator of the hippocampus and can cause long term potentiation. Inhibition of opioid activity by continuous naloxone infusion facilitates weight gain in anorexia and in some will abolish the compulsive drive. Other opioid antagonists need to be found for the more severe compulsive behaviour patients.