Brain and conscious representation of outside reality

doi:10.1016/0028-3932(81)90020-8

Neuropsychologia

Volume 19, Issue 4, 1981, Pages 543-551

https://doi.org/10.1016/0028-3932(81)90020-8 Get rights and content

Abstract

Right brain-damaged patients with contralateral neglect proved unable to describe accurately the left half of recollected images. Analogical brain processes seem therefore to underlie these representations. It is suggested that the left half of the spatial framework of visual representations is impaired in these patients. The alternative explanation based on the unilateral involvement of a hypothetical scanning of inner images is criticized.

Résumé

Des malades avec lésions droites et négligence controlatérale se sont révélés incapables de décrire exactement la moitié gauche des images revisualisées. Des processus analogiques cérébraux semblent donc sous-tendre ces représentations. On suggère que la moitié gauche du cadre spatial des représentations visuelles est perturbée chez ces malades. On critique une autre interprétation fondée sur le déficit unilatéral d'un hypothétique balayage des images mentales.

Zusammenfassung

Es stellte sich heraus, dass Patienten mit rechtshemisphärischen Läsionen nicht die linke Hälfte von erinnerten Bildern beschreiben können. Analoge Hirnprozesse scheinen daher diesen Repräsentationen zu unterliegen. Es wird vorgeschlagen, dass die linke Hälfte der räumlichen Konstruktion von visuellen Repräsentationen bei diesen Patienten gestört ist. Die alternative Erklärung, basierend auf dem Einfluss eines hypothetischen Scanning von inneren Bildern wird kritisiert.

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Allochiria refers to the mislocation of stimuli to the corresponding position on the opposite side of the body or hemispace. It is most often, although not exclusively, reported in the tactile modality and typically in association with unilateral neglect.
We describe a patient presenting with a 2-year history of topographical disorientation without other cognitive complaints. We conducted a systematic exploration of his topographical problems to identify their cognitive substrate.
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To our knowledge this is the first case of topographical disorientation presenting with selective representational allochiria and the first report of allochiria as an early sign of posterior cortical atrophy. The case sheds light on the cognitive basis of allochiria and on a puzzling clinical presentation of neurodegenerative brain disease.
Unilateral spatial neglect
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Unilateral spatial neglect is a neuropsychological syndrome, more frequent after damage to the right cerebral hemisphere, featuring an impaired ability to orient toward the contralateral left side of space and the body, and the inability to detect and report events from that side, of which patients are not aware. In addition to these defective manifestations, patients may show gratuitous behaviors, which include additional productions, unrelated to the task's demand, such as drawings and repeated marks (perseveration) in exploratory target cancellation tasks. Neglect is a multi-component deficit, whose diverse manifestations share a divide between the attended ipsilateral and the neglected contralateral sides of space. Different pathological mechanisms contribute to neglect, including perceptual and premotor impairments, that may be specific to sensory modality, sector of space, and mental images. Neglect may manifest in different coordinate frames with reference to the body and body parts, and objects (egocentric and allocentric neglect). Spatial neglect is a severely disabling disorder, which interferes with functional recovery from stroke. The neural correlates of neglect include cerebral cortical regions surrounding the sylvian fissure: the posterior inferior-parietal cortex, the temporo-parietal junction, the posterior-superior temporal and the frontal premotor cortices, subcortical gray nuclei and white matter fiber tracts connecting these regions. Neglect is independent of, and cannot be traced back to, sensory and motor deficits, and may be interpreted as a derangement of multiple networks, primarily based in the right hemisphere, supporting spatial attention and representation of space and objects in it.
Aphantasia: The science of visual imagery extremes
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Visual imagery allows us to revisit the appearance of things in their absence and to test out virtual combinations of sensory experience. Visual imagery has been linked to many cognitive processes, such as autobiographical and visual working memory. Imagery also plays symptomatic and mechanistic roles in neurologic and mental disorders and is utilized in treatment. A large network of brain activity spanning frontal, parietal, temporal, and visual cortex is involved in generating and maintain images in mind. The ability to visualize has extreme variations, ranging from completely absent (aphantasia) to photo-like (hyperphantasia). The anatomy and functionality of visual cortex, including primary visual cortex, have been associated with individual differences in visual imagery ability, pointing to a potential correlate for both aphantasia and hyperphantasia. Preliminary evidence suggests that lifelong aphantasia is associated with prosopagnosia and reduction in autobiographical memory; hyperphantasia is associated with synesthesia. Aphantasic individuals can also be highly imaginative and are able to complete many tasks that were previously thought to rely on visual imagery, demonstrating that visualization is only one of many ways of representing things in their absence. The study of extreme imagination reminds us how easily invisible differences can escape detection.
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Neglect manifestations are typically explored in the visual modality. Although they are less commonly investigated tactile deficits also exist, and the aim of this study was to explore neglect in this modality. A haptic object discrimination task was designed to assess whether or not shape perception is impaired in seven right brain damaged patients with or without neglect. Each patient's performance on the object discrimination task was assessed before and after a brief period of prism adaptation, a bottom-up rehabilitation technique known to improve neglect symptoms. The results suggest that a haptic deficit – in the form of substantially more left errors – is present only in patients with neglect. Following prism adaptation, the left bias error rates in neglect patients were substantially reduced, and were similar to those observed in patients without neglect. Moreover, the haptic processing of the right side of objects also improved slightly. This finding suggests an expansion of the effects of prism adaptation to the unexposed, tactile modality supporting the cross-modal central effect hypothesis.
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Citation Excerpt :
The task consists in the setting of the midpoint of horizontally presented segments of different lengths (Bisiach et al., 1976, 1983; Heilman and Valenstein, 1979; Schenkenberg et al., 1980). Drawing by copy (Gainotti et al., 1972), and from memory (Bisiach et al., 1981; Grossi et al., 1989). Currently, touch-screen devices are also used (e.g., Rabuffetti et al., 2002).
Unilateral spatial neglect is a disabling neurologic deficit, most frequent and severe after right-hemispheric lesions. In most patients neglect involves the left side of space, contralateral to a right-hemispheric lesion. About 50% of stroke patients exhibit neglect in the acute phase. Patients fail to orient, respond to, and report sensory events occurring in the contralateral sides of space and of the body, to explore these portions of space through movements by action effectors (eye, limbs), and to move the contralateral limbs. Neglect is a multicomponent higher-level disorder of spatial awareness, cognition, and attention. Spatial neglect may occur independently of elementary sensory and motor neurologic deficits, but it can mimic and make them more severe. Diagnostic tests include: motor exploratory target cancellation; setting the midpoint of a horizontal line (bisection), that requires the estimation of lateral extent; drawing by copy and from memory; reading, assessing neglect dyslexia; and exploring the side of the body contralateral to the lesion. Activities of daily living scales are also used. Patients are typically not aware of neglect, although they may exhibit varying degrees of awareness toward different components of the deficit. The neural correlates include lesions to the inferior parietal lobule of the posterior parietal cortex, which was long considered the unique neuropathologic correlate of neglect, to the premotor and to the dorsolateral prefrontal cortices, to the posterior superior temporal gyrus, at the temporoparietal junction, to subcortical gray nuclei (thalamus, basal ganglia), and to parietofrontal white-matter fiber tracts, such as the superior longitudinal fascicle. Damage to the inferior parietal lobule of the posterior parietal cortex is specifically associated with the mainly egocentric, perceptual, and exploratory extrapersonal, and with the personal, bodily components of neglect. Productive manifestations, such as perseveration, are not a correlate of posterior parietal cortex damage.

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^☆: Research supported by C.N.R. grant 78.01998.04.115.4935.

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Brain and conscious representation of outside reality☆

Abstract

Résumé

Zusammenfassung

Cortex

Cortex

Cortex

Neuropsychologia

Arguments concerning representations for mental imagery

Psychol. Rev.

The relationship between verbal and perceptual codes

The active structural network