5. 体側方突進と pusher 現象

抄録

　The relationship between postural disturbance and vertical perception after cerebrovascular disease remains unclear and studies have only recently begun to be conducted. On the other hand, the symptomatic aspect is evident: body lateropulsion is ipsilateral in the case of caudal brainstem lesions and contralateral in the case of rostral brainstem and cerebral hemispheric lesions. In addition, patients with cerebral hemispheric lesions sometimes show“pusher behavior” in which they resist any attempt to correct their posture and push the body back to the paralyzed side using the healthy limbs, as they have a fear of deviation to the healthy side. The pusher behavior is always accompanied by hemiplegia and is detected in about 10% of cases of hemispheric vascular lesions.

　The pathogenesis of lateropulsion associated with the Wallenberg syndrome has traditionally been suggested to involve a high-level central deficit due to a subjective visual vertical (SVV) tilt of vestibular origin, but more recently it has been interpreted as being the result of neurological deficits at lower levels in the spinocerebellar and vestibulospinal tracts. On the other hand, pusher behavior is a result of a disturbance in the higher central mechanisms involved in the perception of verticality as indicated by the subjective postural vertical (SPV) tilts. However, studies on the direction of the SPV tilts have yielded conflicting results. The first pioneering report of SPV in patients with pusher behavior showed that the SPV is tilted toward the lesion side, and pusher behavior occurs on the paralyzed side to correct it. On the contrary, a subsequent study indicated that pusher behavior is an attempt to adjust oneself from a true vertical to a falsely perceived vertical that is tilted toward the paralyzed side. The SPV is derived from the somatosensory system of the trunk. The main lesion site is thought to be the posterior lateral thalamus and the parietal insula, more common in right hemispheric lesions.

　In recent years, neuroscience of body graviception has been discussed in terms of the internal model, which is thought to play a role in clarifying ambiguous sensory information, integrating information among visual, vestibular, and somatosensory modalities, and summarizing efferent and afferent information. As research tools for evaluation, SVV, SPV, and subjective haptic vertical have been used.