A neuroanatomical model of space-based and object-centered processing in spatial neglect

Disengagement of attention with spatial neglect: A systematic review of behavioral and anatomical findings

The present review examined the consequences of focal brain injury on spatial attention studied with cueing paradigms, with a particular focus on the disengagement deficit, which refers to the abnormal slowing of reactions following an ipsilesional cue. Our review supports the established notion that the disengagement deficit is a functional marker of spatial neglect and is particularly pronounced when elicited by peripheral cues. Recent research has revealed that this deficit critically depends on cues that have task-relevant characteristics or are associated with negative reinforcement. Attentional capture by task-relevant cues is contingent on damage to the right temporo-parietal junction (TPJ) and is modulated by functional connections between the TPJ and the right insular cortex. Furthermore, damage to the dorsal premotor or prefrontal cortex (dPMC/dPFC) reduces the effect of task-relevant cues. These findings support an interactive model of the disengagement deficit, involving the right TPJ, the insula, and the dPMC/dPFC. These interconnected regions play a crucial role in regulating and adapting spatial attention to changing intrinsic values of stimuli in the environment.

Disconnection from prediction: A systematic review on the role of right temporoparietal junction in aberrant predictive processing

The right temporoparietal junction (rTPJ) is a brain area that plays a critical role in a variety of cognitive functions. Although different theoretical proposals tried to explain the ubiquitous role of rTPJ, recent evidence suggests that rTPJ may be a fundamental cortical region involved in different kinds of predictions. This systematic review aims to better investigate the potential role of rTPJ under a predictive processing perspective, providing an overview of cognitive impairments in neurological patients as the consequence of structural or functional disconnections or damage of rTPJ. Results confirm the involvement of rTPJ across several tasks and neurological pathologies. RTPJ, via its connections with other brain networks, would integrate diverse information and update internal models of the world. Against traditional views, which tend to focus on distinct domains, we argue that the role of rTPJ can be parsimoniously interpreted as a key hub involved in domain-general predictions. This alternative account of rTPJ role in aberrant predictive processing opens different perspectives, stimulating new hypotheses in basic research and clinical contexts.

The Ties that Bind: Agnosia, Neglect and Selective Attention to Visual Scale

PURPOSE OF REVIEW

Historical and contemporary treatments of visual agnosia and neglect regard these disorders as largely unrelated. It is thought that damage to different neural processes leads directly to one or the other condition, yet apperceptive variants of agnosia and object-centered variants of neglect share remarkably similar deficits in the quality of conscious experience. Here we argue for a closer association between "apperceptive" variants of visual agnosia and "object-centered" variants of visual neglect. We introduce a theoretical framework for understanding these conditions based on "scale attention", which refers to selecting boundary and surface information at different levels of the structural hierarchy in the visual array.

RECENT FINDINGS

We review work on visual agnosia, the cortical structures and cortico-cortical pathways that underlie visual perception, visuospatial neglect and object-centered neglect, and attention to scale. We highlight direct and indirect pathways involved in these disorders and in attention to scale. The direct pathway involves the posterior vertical segments of the superior longitudinal fasciculus that are positioned to link the established dorsal and ventral attentional centers in the parietal cortex with structures in the inferior occipitotemporal cortex associated with visual apperceptive agnosia. The connections in the right hemisphere appear to be more important for visual conscious experience, whereas those in the left hemisphere appear to be more strongly associated with the planning and execution of visually guided grasps directed at multi-part objects such as tools. In the latter case, semantic and functional information must drive the selection of the appropriate hand posture and grasp points on the object. This view is supported by studies of grasping in patients with agnosia and in patients with neglect that show that the selection of grasp points when picking up a tool involves both scale attention and semantic contributions from inferotemporal cortex. The indirect pathways, which include the inferior fronto-occipital and horizontal components of the superior longitudinal fasciculi, involve the frontal lobe, working memory and the "multiple demands" network, which can shape the content of visual awareness through the maintenance of goal- and task-based abstractions and their influence on scale attention. Recent studies of human cortico-cortical pathways necessitate revisions to long-standing theoretical views on visual perception, visually guided action and their integrations. We highlight findings from a broad sample of seemingly disparate areas of research to support the proposal that attention to scale is necessary for typical conscious visual experience and for goal-directed actions that depend on functional and semantic information. Furthermore, we suggest that vertical pathways between the parietal and occipitotemporal cortex, along with indirect pathways that involve the premotor and prefrontal cortex, facilitate the operations of scale attention.

Visual-Spatial and Verbal Remote Association: An fMRI Study

Although idea connections at verbal and conceptual levels have been explored by remote associates tests, the visual-spatial level is much less researched. This study investigated the visual-spatial ability via Chinese Radical Remote Associates Test (CRRAT), wherein respondents consider the positions of the stimulus and target Chinese radicals. Chinese Compound Remote Associates Test (CCRAT) questions also feature stimuli of a single Chinese character; therefore, it was adopted for comparison to distinguish the roles played by verbal and visual-spatial associations in a remote associative process. Thirty-six adults responded to CRRAT and CCRAT; their brain activities were analyzed. Upon excluding the influence of age, verbal comprehension, and working memory, it was found that the caudate, posterior cingulate cortex, postcentral gyrus, and medial frontal gyrus were activated when the respondents answered CCRAT, but only the caudate showed significant activation when they answered CRRAT. The Chinese radical remote association minus the Chinese compound remote association showed that the middle frontal gyrus, inferior parietal lobule, and precuneus demonstrated significant activation. Therefore, this study demonstrated differences in brain mechanisms between visual-spatial and verbal remote associations.

The importance of the insular cortex for vestibular and spatial syndromes

BACKGROUND AND PURPOSE

The aim of the study was to identify the neuroanatomical correlates and associations of neuropsychological syndromes after acute unilateral right-hemisphere brain lesions. The neuropsychological syndromes considered were orientation in three-dimensional space such as tilts of the subjective visual vertical or of the subjective haptic vertical, pusher syndrome, visual neglect and unawareness of paresis (anosognosia for hemiparesis). These neuropsychological phenomena have been found to occur separately or in different combinations after lesions to the right insular cortex.

METHOD

Magnetic resonance imaging scans were obtained from 82 patients with acute right-hemispheric stroke. A lesion-behavior mapping analysis was conducted to specify the neuroanatomical correlates of the above-mentioned neuropsychological syndromes.

RESULTS

In all analyses of the individual neuropsychological syndromes the insular cortex was affected.

CONCLUSIONS

Thus, the insular cortex is involved in (self-)perception and orientation within a three-dimensional space. Since isolated lesions of the insular cortex did not induce the above neuropsychological phenomena, there have to be other regions involved.

Discrete Patterns of Cross-Hemispheric Functional Connectivity Underlie Impairments of Spatial Cognition after Stroke

Despite intense research, the neural correlates of stroke-induced deficits of spatial cognition remain controversial. For example, several cortical regions and white-matter tracts have been designated as possible anatomic predictors of spatial neglect. However, many studies focused on local anatomy, an approach that does not harmonize with the notion that brain-behavior relationships are flexible and may involve interactions among distant regions. We studied in humans of either sex resting-state fMRI connectivity associated with performance in line bisection, reading and visual search, tasks commonly used for he clinical diagnosis of neglect. We defined left and right frontal, parietal, and temporal areas as seeds (or regions of interest, ROIs), and measured whole-brain seed-based functional connectivity (FC) and ROI-to-ROI connectivity in subacute right-hemisphere stroke patients. Performance on the line bisection task was associated with decreased FC between the right fusiform gyrus and left superior occipital cortex. Complementary increases and decreases of connectivity between both temporal and occipital lobes predicted reading errors. In addition, visual search deficits were associated with modifications of FC between left and right inferior parietal lobes and right insular cortex. These distinct connectivity patterns were substantiated by analyses of FC between left- and right-hemispheric ROIs, which revealed that decreased interhemispheric and right intrahemispheric FC was associated with higher levels of impairment. Together, these findings indicate that intrahemispheric and interhemispheric cooperation between brain regions lying outside the damaged area contributes to spatial deficits in a way that depends on the different cognitive components recruited during reading, spatial judgments, and visual exploration.SIGNIFICANCE STATEMENT Focal damage to the right cerebral hemisphere may result in a variety of deficits, often affecting the domain of spatial cognition. The neural correlates of these disorders have traditionally been studied with lesion-symptom mapping, but this method fails to capture the network dynamics that underlie cognitive performance. We studied functional connectivity in patients with right-hemisphere stroke and found a pattern of correlations between the left and right temporo-occipital, inferior parietal, and right insular cortex that were distinctively predictive of deficits in reading, spatial judgment, and visual exploration. This finding reveals the importance of interhemispheric interactions and network adaptations for the manifestation of spatial deficits after damage to the right hemisphere.

Damage to the right temporoparietal junction, but not lateral prefrontal or insular cortex, amplifies the role of goal-directed attention

Whether an object captures attention depends on the interplay between its saliency and current behavioral predispositions of the observer. Neuroimaging work has implied a ventral attention network, comprising the temporoparietal junction (TPJ), lateral prefrontal cortex (lPFC) and the insula, in attentional orienting toward salient events. Activity of the TPJ is driven by novel and unexpected objects, while the lateral prefrontal cortex is involved in stimulus-driven as well as goal-directed processing. The insula in turn, is part of a saliency network, which has been implicated in detecting biologically salient signals. These roles predict that damage to the TPJ, lPFC, or insula should affect performance in tasks measuring the capture of attention by salient and behaviorally relevant events. Here, we show that patients with lesions to the right TPJ have a characteristic increase of attentional capture by relevant distracters. In contrast, damage to the lPFC or insular cortex only increases reaction times, irrespective of the task-relevant properties of distracters. These findings show that acquired damage to the TPJ pathologically amplifies the capture of attention by task-relevant information, and thus indicate that the TPJ has a decisive role in goal-directed orienting.

Apraxia, Neglect, and Agnosia

PURPOSE OF REVIEW

In part because of their striking clinical presentations, disorders of higher nervous system function figured prominently in the early history of neurology. These disorders are not merely historical curiosities, however. As apraxia, neglect, and agnosia have important clinical implications, it is important to possess a working knowledge of the conditions and how to identify them.

RECENT FINDINGS

Apraxia is a disorder of skilled action that is frequently observed in the setting of dominant hemisphere pathology, whether from stroke or neurodegenerative disorders. In contrast to some previous teaching, apraxia has clear clinical relevance as it is associated with poor recovery from stroke. Neglect is a complex disorder with many different manifestations that may have different underlying mechanisms. Neglect is, in the author's view, a multicomponent disorder in which impairment in attention and arousal is a major contributor. Finally, agnosias come in a wide variety of forms, reflecting impairments ranging from low-level sensory processing to access to stored knowledge of the world (semantics).

SUMMARY

The classic behavioral disorders reviewed here were of immense interest to early neurologists because of their arresting clinical phenomenology; more recent investigations have done much to advance the neuroscientific understanding of the disorders and to reveal their clinical relevance.

What role for prism adaptation in the rehabilitation of pure neglect dyslexia?

Prism adaptation (PA) has been successfully applied in the rehabilitation of spatial neglect, with significant transfer to classic neglect tests and activities of daily living. However, well-controlled studies were unable to replicate these findings, and recent reports suggest that PA may affect selectively visuo-motor symptoms. Here, a patient with pure left neglect dyslexia was tested before, immediately after, and 24 h after PA. Despite a significant adaptation aftereffect adaptation had no effect omissions, substitutions and letter-based errors. PA does not affect pure neglect dyslexia and should therefore be reserved for the rehabilitation of motor-intentional, rather than visual-attentional symptoms.