Funded Grants

Spatial awareness: Normality, pathology and rehabilitation

Hemispatial neglect is a highly disabling condition that frequently occurs following brain damage, particularly of the right hemisphere. It affects up to 85% of right hemisphere stroke patients in the acute phase and 69% in the rehabilitation phase. Neglect is often accompanied by "extinction", a paradigmatic example of how stimuli can compete for conscious awareness, whereby patients lose awareness of contralesional stimuli when ipsilesional stimuli are presented concurrently. The neglect syndrome is characterised by severed awareness of sensory inputs from the left affected space, even though there may be no primary sensory loss. Patients fail to orient and respond to stimuli, often behaving as if the left side of their conscious experience no longer exists. The real-life implications of neglect can be devastating, with patients failing to eat food off the left side of their plate, only dressing the right half of their bodies, and not recovering as well as expected from stroke-related motor deficits. Promising rehabilitation techniques have recently become available (e.g., prism adaptation and brain stimulation), but their potential is limited because the pathophysiological mechanisms of neglect and extinction are still poorly understood.

Here, I propose a research program that is focused around the competitive feature of spatial sensory perception, something which remains largely unaddressed despite it being at the core of the pathophysiology of neglect. Healthy people are not as good at perceiving double simultaneous compared to single stimuli, suggesting extinction following stroke may be a pathological exacerbation of a physiological competitive perceptual mechanism. The program builds upon this physiologically limited capacity of the normal brain and is articulated around four main branches: 1) exploiting this limited capacity phenomenon to characterise the cognitive and neural processes of normal and pathological spatial awareness; 2) pursuing a multisensory perspective (neglect and extinction do not only occur in the visual domain), 3) providing an animal model of physiological and pathological spatial awareness, and 4) developing new therapeutic interventions based on brain stimulation and pharmacological agents. The findings of this research program will have important implications within both basic and applied research fields. They will substantially contribute to our understanding of the fundamental principles governing human competitive perception of multisensory inputs in the normal brain. The proposed approach, in which identical behavioral paradigms will be applied to healthy and brain-damaged subjects, as well as neurologically intact and temporarily lesioned animals, will provide a full comparative dataset concerning clinically-relevant cognitive processes and their underpinning neuronal mechanisms. In terms of rehabilitation, the physiological mechanisms of currently used therapies will be identified by examining their effects on competitive perception. In the longer term, new brain-stimulation and pharmacological interventions will also be tested. These advances will be readily exploitable for the development of new neuroscience-driven approaches for the treatment of deficits in spatial awareness.