A demonstration of endogenous modulation of unilateral spatial neglect: The impact of apparent time-pressure on spatial bias

Abstract

Unilateral neglect, a lack of awareness for one side of space, is a common and debilitating consequence of stroke. Previous work has identified a relationship between enduring left neglect and diminished general alertness and shown that increasing alertness can temporarily reduce the severity of the spatial bias. In that research, alertness was modulated by loud tones or with pharmacological stimulants. Here we examine whether cognitive, endogenously driven changes can produce similar short-term improvements. Time-pressure is associated with increased subjective arousal and increased activation in cortical regions associated with alertness. Here five patients completed a spatial cancellation task with and without instructions regarding a time limit. Significant reductions in neglect severity were observed when patients believed that they were acting under time-pressure, despite the conditions being equivalent in the actual (unlimited) time available. Functional imaging work has highlighted the secondary effects that damage to networks mediating alertness can have on structurally intact spatial systems. The results here suggest that activation of presumably spared function in these damaged networks can induce moment-by-moment changes in spatial function and, crucially, that this can be achieved using entirely endogenous means. (JINS, 2008, 14, 33-41.)

Losing the left side of the world: Rightward shift in human spatial attention with sleep onset

“…This would be consistent with both the normal and clinical literature on lateralised shifts with low alertness and distraction15161720212228 and studies showing disengagement of prefrontal and parietal regions345 with consequent reduction in cognitive control and target detection29. The magnitude and reliability of the rightward shift reported here suggests a tractable method for examining this directionally specific effect, including its relationship with hemispheric specialisation in other functions such as language.…”

“…There may be a number of reasons for this including right-hemisphere dominance in aspects of spatial cognition and attention (making it more able to compensate for left hemisphere damage than vice versa12) and prolongation of neglect by co-occurring deficits in alertness, themselves associated with right hemisphere function1314. The latter argument has been supported by temporary amelioration in rightward bias that follows exposure to stimulating noises, thoughts or medication151617.…”

Recent advances in the understanding of neglect and anosognosia following right hemisphere stroke

“…When the time restrictions and feedback were removed, prism adaptation resulted in improvements on standard neglect measures. However, in another study, a time-pressure component showed a positive effect on a spatial cancellation task [31]. Specifically, in this study the participants were asked to complete a spatial cancellation task with and without instructions regarding a time limit.…”

Dissociable effects of attention vs working memory training on cognitive performance and everyday functioning following fronto-parietal strokes

“…Patient data from both our group (Duncan et al, 1999;Peers et al, 2005) and others (Habekost & Rostrup, 2006;Corbetta & Shulman, 2002;Robertson et al, 1997a) indicate that pathological spatial biases tend to arise and persist in the context of more general attentional impairment. Interventions that manipulate general attentional resources, for example increasing alertness via stimulants or stimulation (George, Mercer, Walker, & Manly, 2008;Gorgoraptis et al, 2012) or reducing alertness with sleep onset (Bareham, Manly, Pustovaya, Scott, & Bekinschtein, 2014), have been shown to phasically modulate spatial bias, suggesting rather direct interactions between these components. Despite not explicitly targeting spatial bias, therefore, it may be possible to improve spatial functions by focussing on other aspects of attention.…”