Pusher behaviour: a critical review of controversial issues.

Despite an increasing interest by researchers and clinicians, the pusher behaviour (PB) is still a poorly understood disorder, exhibited by some stroke patients, who push with their non-affected limbs towards the contralesional side and resist attempts at correction of their tilted posture. This review is aimed at critically summarizing findings on controversial issues regarding PB, namely correlation with neglect, neural correlates and underlying mechanisms. There is a growing agreement that PB reflects some misrepresentation of verticality. According to different findings, it has been suggested that PB may result from a conflict between an intact visual and an impaired somesthetic perception of vertical, or alternatively that it might result from a high-order disruption of somesthetic information processing from the paretic hemi-body, named graviceptive neglect. Although conflicting data have been reported, the association between PB and neglect seems to be confirmed, when a comprehensive assessment of neglect-related phenomena is performed. Localization of brain lesions is also controversial. Some investigations stressed the role of posterior lateral thalamus, but other findings revealed that different lesional sites may also be present. On the basis of these data we suggest the existence of a multicomponential network reliable for upright posture control. This model might also explain some different results in this area. Clinical implications and requirements for future research are discussed.