The Nature of Consciousness in the Visually Deprived Brain

Abstract

Vision plays a central role in how we represent and interact with the world around us. The primacy of vision is structurally imbedded in cortical organization as about one-third of the cortical surface in primates is involved in visual processes. Consequently, the loss of vision, either at birth or later in life, affects brain organization and the way the world is perceived and acted upon. In this paper, we address a number of issues on the nature of consciousness in people deprived of vision. Do brains from sighted and blind individuals differ, and how? How does the brain of someone who has never had any visual perception form an image of the external world? What is the subjective correlate of activity in the visual cortex of a subject who has never seen in life? More in general, what can we learn about the functional development of the human brain in physiological conditions by studying blindness? We discuss findings from animal research as well from recent psychophysical and functional brain imaging studies in sighted and blind individuals that shed some new light on the answers to these questions.

Enhanced heat discrimination in congenital blindness

“…Previous studies have attributed the increased performance in various non-visual sensory tasks in congenitally blind subjects to the recruitment of the occipital cortex [1]. In addition, congenitally blind subjects also show increased occipital activity at rest [29]. If we assume that the increased performance in thermal discriminability is due to a similar mechanism of occipital recruitment, we propose that stimulating a small skin area is insufficient to bring neuronal activity within the occipital cortex above the physiological noise level.…”

Pain Perception Is Increased in Congenital but Not Late Onset Blindness

“…The extent of these neuroplastic changes depends more strongly on the onset than on the duration of visual deprivation [9]–[12]. These findings have been corroborated by recent behavioral and brain imaging studies in humans showing that early blindness leads to compensatory plasticity and to a reorganization of the visual cortex [13], [15]. In sharp contrast, studies on late blindness have led to conflicting results.…”

Spatial imagery relies on a sensory independent, though sensory sensitive, functional organization within the parietal cortex: A fMRI study of angle discrimination in sighted and congenitally blind individuals

“…Both the conjunction maps at individual and group levels showed in congenitally blind individuals an overlapping cross-modal recruitment in ventrotemporal, temporo-occipital and dorsal occipital regions across sensory modalities, as shown for a wide gamut of non-visual perceptual and cognitive tasks (reviewed, among others, in Cattaneo and Vecchi, 2011;Kupers et al, 2011b;Merabet and Pascual-Leone, 2010;Noppeney, 2007;Pietrini et al, 2009;Ricciardi and Pietrini, 2011;Collignon et al, 2011).…”