A series of examinations were carried out to determine whether the limbic system, particularly the hippocampus and the amygdaloid nucleus, participates in the production of disequilibrium of the eyes and the body and to clarify the conditions which induce disequilibrium. Over-stimulation of the rabbit's hippocampus induces over-excitation of adrenergic components involved in this part of the brain, through which dysfunction of equilibrium center in the brain stem is eventually brought about. This dysfunction leads to disequilibrium of the eyes and the body. On the basis of these results, equilibrium tests for neurotic vertigo were devised. Using these equilibrium tests we noted that in a certain group of traumatized patients who suffer from vertigo of psychosomatic origin, there are two etiological factors: functional linkage between the temporal cortex and the limbic system, particularly the hippocampus in regard to a memory or a conditioned reflex relevant to vertigo, over-excitation of the adrenergic components involved in the brain connecting the hippocampus, the hypothalamus and equilibrium centers in the brain stem. These two etiological factors induce disequilibrium by a trigger-and-target relationship in which the former acts as a trigger and the latter as a target. The cerebellum is not an essential factor in producing vertigo of psychosomatic origin, but it enhances vertigo of this type through activation of the adrenergic components, particularly those in the hippocampus. Thus, in patients with both vertigo of psychosomatic origin and cerebellar symptoms recovery from vertigo tends to be delayed. Over-stimulation of the rabbit's amygdaloid nucleus, particularly its medial portion and the habenular nucleus induces over-excitation of adrenergic components involved in these parts of the brain. These animals develop disequilibrium of the eyes in response to an olfactory stimulus, such as extract of garlic. On the basis of these results, equilibrium tests for olfactory vertigo were devised. Using these equilibrium tests we noted that traumatized patients who suffered from vertigo due to inhalation of garlic vapor showed hyper-reactivity to adrenaline and developed disequilibrium of the eyes and the body when given a subcutaneous injection of this drug. These findings indicate that olfactory vertigo is induced by a mechanism in which olfactory stimulation affects the above adrenergic components, causing disequilibrium of the eyes and the body.(ABSTRACT TRUNCATED AT 400 WORDS)