Allocentric neglect strongly associated with egocentric neglect.

To access publisher's full text version of this article. Please click on the hyperlink in Additional Links field.Following brain injury, many patients experience egocentric spatial neglect, where they fail to respond to stimuli on the contralesional side of their body. On the other hand, allocentric, object-based neglect refers to the symptom of ignoring the contralesional side of objects, regardless of the objects' egocentric position. There is an established tradition for considering these two phenomena as both behaviorally and anatomically dissociable. However, several studies and some theoretical work have suggested that these rather reflect two aspects of a unitary underlying disorder. Furthermore, in a recent large study Yue et al. [Archives of Physical Medicine and Rehabilitation 93 (2012) 156] reported that acute allocentric neglect is only observed in cases where substantial egocentric neglect is also present. In a new sample of right hemisphere stroke patients, we attempted to control for potential confounds by using a novel continuous measure for allocentric neglect (in addition to a recently developed continuous measure for egocentric neglect). Our findings suggest a strong association between egocentric and allocentric neglect. Consistent with the work of Yue et al. (2012), we found allocentric behavioral deficits only in conjunction with egocentric deficits as well as a large corresponding overlap for the anatomical regions associated with egocentric and with allocentric neglect. We discuss how different anatomical and behavioral findings can be explained in a unified physiologically plausible framework, whereby allocentric and egocentric effects interact.National Institutes of Health NS054266 DC009571 Deutsche Forschungsgemeinschaft KA 1258/10-1 HA 5839/3-1 PAK 270/

Trunk rotation affects temporal order judgments: evidence from spatial neglect

Spatial neglect is a common consequence of brain injury where individuals fail to respond to stimuli presented on their contralesional side. It has been argued that beyond the spatial bias, these individuals also tend to exhibit temporal perceptual deficits. Here we demonstrate that the deficits affecting the temporal dynamics of attentional deployment are in fact modulated by spatial position. Specifically, we observed the severe bias to the right affecting the time-course of visual awareness in chronic neglect is enhanced when stimuli are presented on the contralesional side of the trunk, while keeping retinal and head-centered coordinates constant. We did not find this pattern in right brain damaged patients without neglect or in patients who had recovered from neglect. Our work suggests that the temporal attentional deficits observed in neglect are heavily modulated by egocentric spatial position. This provides strong evidence against models that suggest independent modules for spatial and temporal attentional functions, while also providing strong evidence that trunk position plays a dominant – if not the principal – role in spatial neglect

Unravelling the high-dimensional structure of spatial neglect and visuospatial attention: A multivariate approach to lesion-behaviour mapping

One of the most studied and elaborated neurological disorders after stroke is probably spatial neglect, a disorder of spatial exploration, attention and awareness occurring in about two third of all right hemispheric stroke patients. A characteristic symptom these patients show is a failure to orient or respond to information on the contralesional side of space including a general orientation to the ipsilesional side. It is still not possible to come to a common consensus regarding this syndrome on theoretical, anatomical and behavioural aspects. The investigation of the anatomical substrates of spatial neglect, however, offers chances to shed light on crucial pathophysiological processes and inform theoretical models. Therefore, a complete research field dedicated several decades of research to the question where in the brain the syndrome of spatial neglect might have its´ pathogenesis and how this information can help us to understand cognitive processes of normal spatial exploration and attentional processing. A method which largely contributed to this field is called lesion-behaviour mapping by drawing statistical inference about the functional brain architecture from focal brain damage. Following the development within the last five to ten years, a new era of computerised lesion-behaviour mapping techniques became widely available, allowing to reiterate and challenge previous findings and to account for the high-dimensional information present in brain lesions. In my thesis I employed these new techniques to unravel the anatomical substrates of the syndrome of spatial neglect and related spatial attentional deficits. I want to show that these methods can be deployed to make valuable contributions to the understanding of the pathophysiology of the syndrome. In my first empirical work, the presence of a large right-hemispheric network related to the behavioural severity of spatial neglect can be confirmed, closing longstanding controversies. It shows that multivariate machine-learning based lesion-behaviour mapping techniques are particularly suited to detect critical brain areas and to evaluate the predictive performance of underlying statistical models. In the second and third empirical work, I complemented these primary findings by applying the same statistical methodology to parameters of remote disconnection and to different diagnostic tools in the assessment of spatial neglect. These works show crucial areas and anatomical hubs severely disconnected to other areas of the brain and contributing to the development of lateralised deficits in spatial neglect patients. Finally, with the last empirical work, contributions to controversial views concerning the anatomical substrates of the extinction phenomenon, a further spatial attentional deficit, were made. By evaluating lesion-behaviour relationships in spatial neglect, as it was done in the present thesis, it will become possible to inform clinical staff how to direct patients to more effective management and treatment schedules, essential for rehabilitation, while spatial neglect generally is considered as a negative prognosis factor for stroke recovery