Psychoanatomical substrates of Balint's syndrome

Abstract

Objectives: From a series of glimpses, we perceive a seamless and richly detailed visual world. Cerebral damage, however, can destroy this illusion. In the case of Bálint's syndrome, the visual world is perceived erratically, as a series of single objects. The goal of this review is to explore a range of psychological and anatomical explanations for this striking visual disorder and to propose new directions for interpreting the findings in Bálint's syndrome and related cerebral disorders of visual processing. Methods: Bálint's syndrome is reviewed in the light of current concepts and methodologies of vision research. Results: The syndrome affects visual perception (causing simultanagnosia/visual disorientation) and visual control of eye and hand movement (causing ocular apraxia and optic ataxia). Although it has been generally construed as a biparietal syndrome causing an inability to see more than one object at a time, other lesions and mechanisms are also possible. Key syndrome components are dissociable and comprise a range of disturbances that overlap the hemineglect syndrome. Inouye's observations in similar cases, beginning in 1900, antedated Bálint's initial report. Because Bálint's syndrome is not common and is difficult to assess with standard clinical tools, the literature is dominated by case reports and confounded by case selection bias, non-uniform application of operational definitions, inadequate study of basic vision, poor lesion localisation, and failure to distinguish between deficits in the acute and chronic phases of recovery. Conclusions: Studies of Bálint's syndrome have provided unique evidence on neural substrates for attention, perception, and visuomotor control. Future studies should address possible underlying psychoanatomical mechanisms at "bottom up" and "top down" levels, and should specifically consider visual working memory and attention (including object based attention) as well as systems for identification of object structure and depth from binocular stereopsis, kinetic depth, motion parallax, eye movement signals, and other cues.

Exploring the world with Bálint syndrome: biased bottom-up guidance of gaze by local saliency differences

“…If the priority map is crucial for the selection of sensory contents by attention, damage to this representation, in particular if it is bilateral, should have devastating consequences on spatial attention. this is indeed what happens in patients with Bálint syndrome, who in severe cases are described as virtually blind due to their failure to select stimuli for conscious processing (Rizzo and Vecera 2002;holmes and horrax 1919;Kim and Robertson 2001). however, it is unclear why bilateral damage to the parietal priority map should result in a strong ocular bias towards central regions (or 'sticky' fixation).…”

“…how can 'sticky' fixation during ocular exploration be explained? some authors (Rafal 1997;Rizzo and Vecera 2002) proposed that oculomotor apraxia is due to a pathological constriction of visual attention to a single object. according to this hypothesis, patients make erratic eye movements because of a reduced 'spatial window' of attention (Dalrymple et al 2013a) and consequently the failure to disengage attention from a fixated object.…”

“…Following the initial description, many authors also noted impaired initiation and control of saccadic eye movements in patients with Bálint syndrome (oculomotor apraxia;luria et al 1963;Girotti et al 1982;Rafal 1997;Rizzo and Vecera 2002). Oculomotor apraxia is evidenced as a failure to disengage gaze from a fixated object (sometimes described as 'sticky' fixation), making it often impossible to look at objects shown in the visual periphery, or conversely the failure to maintain fixation on a given object.…”

Binding, spatial attention and perceptual awareness

“…Balint's syndrome has been most often associated with occipital-parietal damage and centred in the angular gyrus 82 , but neglect has been more often associated with temporal-parietal damage and centred in the supramarginal gyrus 83 . It therefore seems plausible that unilateral neglect and Balint's syndrome reflect different underlying deficits.…”

A Rare Syndrome: Balint Syndrome

“…Çünkü sendromun semptomlarında bireysel farklılıklar görülmüştür. Sendromun bireysel semptomlarını sadece ayırmak değil, ayrıca oldukça geniş kategoride sunulan defisitleri standart nöropsikolojik testlerle değerlendirmek sıklıkla zordur ve bireysel vakalar arasında önemli çeşitlilik vardır [16][17][18].…”