 The third ventricle hypothesis of depression proposes that the behavioural cluster associated with depression (hunched posture, avoidance of eye contact, reduced appetites for food and sex plus social withdrawal and sleep disturbance) serves to reduce an individual's attack-provoking stimuli within the context of a chronically hostile social environment.It further proposes that this response is mediated by the acute release of an unknown (probably cytokine) inflammatory agent into the third ventricular space.In support of this suggestion imaging studies reveal that the third ventricle is enlarged in depressives.