Ipsilesional 'where' with contralesional 'what' neglect

Whereas contralesional spatial neglect is usually caused by right temporo-parietal lesions, ipsilesional spatial neglect is induced primarily by right frontal lesions. This report describes a 73-year-old woman with a right inferior parietal lesion who on 'where' tasks (line bisection and midline pointing) demonstrated ipsilesional neglect, but on 'what' tests (gap vs. no-gap detection cancellation and clothing tape removal) demonstrated contralesional neglect. This 'what' and 'where' directional dissociation provides evidence for independent 'what' and 'where' attentional networks; however, the reason this parietal lesion causes this contralesional vs. ipsilesional spatial attentional 'what' and 'where' dichotomy remains to be determined.     

Increased attentional demands impair contralesional space awareness following stroke

Rate and severity of contralesional loss of awareness following stroke is highly variable across patients and assessment methods. We studied whether the degree of impairment for contralesional space awareness depends on the quantity of attentional resources that are available for task performance. A new computer-based paradigm was used to assess visual extinction and single-target detection rate in four right hemisphere stroke patients. In the single-task condition, they had to report only the position of the target(s) (“right”, “left”, or “both” sides). In the dual-task conditions, patients also performed a second task, visual or auditory, that recruited additional attentional resources. The same tasks were also performed by healthy controls and by a left hemisphere stroke patient. Patients’ performance was apparently unimpaired in the single-task condition. In contrast, dramatic failures to report the left-sided target emerged in the dual-task conditions. The performance of control participants was unaffected by the dual-task manipulation, whereas the left stroke patient showed the opposite pattern (i.e., unawareness of right-sided targets). Severe contralesional space unawareness under dual-task conditions reveals that visuospatial deficits can dramatically emerge when attentional resources are consumed by a concurrent task. Apparently spared contralesional awareness may simply reflect the availability of resources that are just sufficient to perform a single-task. This finding has important implications for the assessment of contralesional space awareness following stroke, because everyday life activities are often more demanding than most of the tests adopted for diagnosing space awareness disorders.     

Changing attentional demands in left hemispatial neglect.

Seven variations of a letter cancellation test were used to examine how varying attentional demands affect hemispatial neglect in patients with right hemisphere lesions. While the 14 targets always remained in the same location, the number of distractors (zero, nine, 28, or 82) as well as their complexity (one letter or nine different letters) were varied. The percentage of targets canceled in the left hemispace was linearly related to the number of distractors. There were no differences between the complexity conditions. In a second study, the same 14 targets were presented but the distractors (zero, 14, or 41) were all placed on the right. Increasing the number of distractors on the right increased neglect on both sides of the space. Taken together, these results suggest that, while the limited attentional resources of the left hemisphere are biased toward the right hemispace, the absence of contralateral attentional demands allows these resources to be directed ipsilaterally.     

Ipsilesional attentional-approach neglect or crossover effect

Patients with ipsilateral neglect (IN) bisect lines toward contralesional space. It has been posited that IN might be induced by an attempt at compensation, as part of the crossover effect, where patients with an ipsilesional bias when bisecting long lines, cross over and develop a contralesional bias on short lines or as a release of an approach (grasp) behavior that might be attentional or intentional. To test these alternative hypotheses we had a patient with IN from a right medial frontal lesion bisect lines that contained no cue, a left-sided cue, a right-sided cue, and bilateral cues. If this patient had ipsilateral neglect (IN) because of a crossover effect or compensation, right-sided cues should have influenced bisection more than left-sided cues. We, however, found that only left-sided cues induced a significant change (left-sided deviation) providing support for the attentional-approach (grasp) hypothesis. Further support of this contralesional attentional grasp hypothesis comes from the observation that this patient also had ipsilesional extinction to simultaneous stimuli.     

Ipsilesional neglect: behavioural and anatomical features

OBJECTIVE: To learn more about the behavioural and anatomical features of ipsilesional neglect. METHODS: Thirty consecutive patients with spatial neglect were tested on cancellation and line bisection tasks. To learn if patients with ipsilesional neglect demonstrate the sensory-attentional or motor-intentional type of neglect, a video apparatus was used that dissociates these determinants. RESULTS: Five patients showed evidence of ipsilesional neglect. This phenomenon was seen only on the line bisection task. All patients with ipsilesional neglect had lesions involving frontal-subcortical regions. Although ipsilesional neglect evolved from early in three of five cases, the other patients displayed ipsilesional neglect without initial contralateral neglect, suggesting that ipsilesional neglect cannot be fully attributed to a compensatory strategy. The results of the tests that used the video apparatus indicate that right sided frontal or subcortical injury may induce contralateral attentional or intentional "approach" behaviours. CONCLUSIONS: Ipsilesional neglect is most often associated with frontal-subcortical lesions, cannot be entirely attributed to a compensatory strategy, and may be induced by an attentional bias, an intentional bias, or both.     

Ipsilesional intentional neglect and the effect of cueing

BACKGROUND: Contralesional hemispatial neglect may be induced by an attentional deficit where patients are inattentive to or unaware of stimuli in contralesional hemispace, an intentional deficit where patients are unable to act in or towards contralesional hemispace, or both. The deficits associated with ipsilesional neglect have not been as well characterized. Because cueing may be used as a rehabilitative assistive device, we wanted to learn whether the efficacy of an attentional or intentional cue was related to the type of bias. METHODS: We studied a patient with a right frontotemporal stroke who had ipsilesional neglect by using a video apparatus that dissociates sensory-attentional and motor-intentional systems. We also performed a cueing experiment with primarily sensory-attentional cues (i.e., read the letter at the end of the line) and primarily motor-intentional cues (i.e., touch the end of the line). RESULTS AND CONCLUSIONS: Ipsilesional neglect was primarily a motor-intentional deficit with a motor-action bias to the left and a secondary sensory-attentional bias for stimuli to the right. With cueing we found a double dissociation: the rightwards motor-intentional cue improved the primary left-sided intentional bias and the leftwards sensory-attentional cue improved the secondary right-sided attentional bias. Effective rehabilitation strategies need to address both sensory-attentional and motor-intentional deficits in patients with neglect.     

Ipsilesional and contralesional sensorimotor function after hemispherectomy: differences between distal and proximal function

Previous studies have reported mainly on contralesional somatosensory and motor function after hemispherectomy. So far, ipsilesional impairments have received little attention even though these have been reported in patients with less extensive lesions. In the current study we assessed ipsilesional and contralesional sensorimotor function in a group of 12 patients with hemispherectomy. In addition, we focused on differences between distal and proximal function and investigated several factors that may have contributed to individual differences between patients. The tests included tapping, force production, tactile double simultaneous stimulation, pressure sensitivity, passive joint movement sense and sensitivity to hot and cold. Ipsilesional impairments were found on all tests, except passive joint movement sense. Unexpectedly, no significant ipsilateral distal-proximal gradient was found for any of the measures. Both the removal of the diseased cerebral hemisphere and possible changes to the remaining brain structures may have affected ipsilesional sensorimotor function. Contralesional performance was impaired on all tests except for passive joint movement in the shoulder. The contralesional impairments were characterized by a distal-proximal gradient measured on all tests, except that of sensitivity to hot and cold. Distal function was always most impaired. The difference between distal and proximal motor function is in agreement with the established concepts of the motor pathways, with the motoneurons innervating proximal muscles receiving bilateral cortical and subcortical input. Age at onset of original brain damage correlated significantly with passive joint movement sense. Patients with known abnormalities to the remaining brain structures performed inferior on the tapping test only. No effect was found of the hemispheric side of removal.     

Prism adaptation can improve contralesional tactile perception in neglect

The authors show that prismatic adaptation can reduce tactile inattention in stroke patients with unilateral neglect. Four patients with visuospatial neglect and tactile extinction underwent 10-minute application of 20 degrees right-shifting prismatic lenses during pointing. This improved contralesional tactile perception in all patients, even for a task requiring no exploration or spatial motor responses. This finding suggests a potential role for prismatic adaptation in the rehabilitation of multiple sensory modalities in patients with neglect.     

Paradoxical extension into the contralesional hemispace in spatial neglect

To explore the idea of a perceptual distortion of space in spatial neglect, neglect patients, age-matched healthy controls and right hemisphere control patients judged the vanishing point of horizontally and vertically-moving stimuli. Hemifield of presentation and movement direction of the stimulus presentation was manipulated. The results suggest that neglect patients show a stronger response bias in the direction of the moving stimuli ("representational momentum") than healthy and right hemisphere controls. Furthermore, neglect patients, but not the control groups, showed a direction-specific response whereby the presence of neglect was associated with a larger representational momentum for leftward-moving stimuli. The one left-hemisphere patient with right-sided neglect showed the opposite effect. Thus, neglect patients showed a relative overextension into their neglected side of space. While these findings are in line with the idea of an extension in the representation of contralesional space, other explanations such as deficient spatial remapping, impairments in smooth pursuit and distortions in memorized visuo-motor movements are considered.     

Brain stimulation procedures for treatment of contralesional spatial neglect

The application of brain stimulation techniques for modulation of cortical excitability changes underlying spatial neglect following right-brain-damage has been the first application of brain stimulation in the rehabilitation setting. Several factors concur in making neglect a prototype of cognitive disorders that can be modulated by brain stimulation: 1) neglect is highly lateralized deficit, 2) neglect is a network disorder in which lesion of a network node impacts affects excitability of intrahemispehric and interhemispheric connections, and 3) lesions of the right hemisphere, the most frequent cause of neglect, are associated with a transcallosally mediated increase of facilitation of the left hemisphere more frequently than are lesions of the left hemisphere associated with right hemisphere facilitation. We review the main applications of TMS for modulation of neglect disorder and we discuss the different potentialities of inhibition of the unaffected and facilitation of the affected hemisphere. Moreover, we suggest potential interactions of TMS with other behavioral techniques in the rehabilitation setting.     

Ipsilesional and contralesional regions participate in the improvement of poststroke aphasia: a transcranial direct current stimulation study

In the past few years, noninvasive cerebral stimulations have been used to modulate language task performance in healthy and aphasic patients. In this study, a dual transcranial direct current stimulation (tDCS) on anterior and posterior language areas was applied for 2 weeks to a patient with a possible crossed aphasia following a right hemisphere stroke. Inhibitory cathodal stimulation of the right Brodmann areas (BA) 44/45 and simultaneous anodal stimulation of the left BA 44/45 improved the patient’s performance in picture naming. Conversely, the same bilateral montage on BA 39/40 did not produce any significant improvement; finally, electrode polarity inversion over BA 39/40 yielded a further improvement compared with the first anterior stimulation. Our findings suggest that ipsilesional and contralesional areas could be useful in poststroke functional reorganization and provide new evidences for the therapeutic value of tDCS in aphasia.     

Hand-centered attentional and motor asymmetries in unilateral neglect

On several accounts of "selection for action", acting on a target object among distractors requires that irrelevant inputs and responses to these inputs are inhibited, and relevant inputs and responses selected. In unilateral neglect associated with right-hemisphere lesions, selection processes may be biased toward stimuli on the right, as right is usually defined by head and body hemispace. In normal subjects performing reaching-to-target tasks, selection may be "hand-centered" (Tipper S., Lortie C., Baylis G.C., Journal of Experimental Psychology: Human Perception and Performance 18(4) (1992) 891-905) in that distractor stimuli close to the hand compete strongly with the target for the control of action, causing greater interference than distractors far from the hand. We reasoned that in the context of a reaching task, a left-right asymmetry in unilateral neglect may be defined with respect to the position of the hand. This predicts that target and distractor stimuli to the left of hand (i.e. requiring leftward movements for contact) should compete less strongly for the control of action than stimuli to the right of the hand. We tested this hypothesis by asking eight patients with unilateral neglect (and 12 healthy controls) to reach to central targets presented alone and with surrounding distractors from left or right start positions. Patients with neglect, but not controls, were slower to initiate reaches from right start as compared to left start positions. In this context, patients showed interference from distractors to the right of the hand and facilitation from distractors to the left of the hand. This indicates that a left-right selection asymmetry in neglect may be hand-centered. These data can be explained on a model of damage to the portion of a distributed neuronal population coding movement vectors to stimuli in relatively leftward locations.     

Expectation-based attentional modulation of visual extinction in spatial neglect

Visual extinction, the failure of patients with unilateral focal brain damage to report the contralesional of two simultaneously presented stimuli, may be modulated by characteristics of the display such as similarity, collinearity, or connectedness. Since these factors affect the perceptual configuration of stimuli, the modulation of extinction is believed to reflect low-level perceptual grouping. In the present study, patient AG did not show any modulation of contralesional detection when the ipsilesional and contralesional stimulus grouped by colour, by form, or both (Experiment 1). In contrast, identification of the contralesional stimulus was facilitated when the stimuli grouped (Experiment 2), suggesting a modulation of extinction by specific task demands. Experiment 3 used a cueing procedure to demonstrate modulation of extinction by expectation biases. Prior to stimulus presentation, AG was cued to attend to a particular feature (e.g. colour). After stimulus exposure he was prompted to identify the expected feature on valid trials and the unexpected feature on invalid trials. AG showed a significant validity effect for contralesional stimuli i.e. he identified the expected feature (e.g. colour) significantly better than the unexpected feature (e.g. form). These results suggest that competition for selection between visual stimuli may not only be influenced by perceptual characteristics of the display, but also by high-level factors such as the response criterion or expectation biases.     

Imaging the attentional blink: perceptual versus attentional limitations

Imaging studies of conscious perception using techniques such as masking often show increased neural responses in object processing regions of the brain, and accompany increased awareness of the stimulus. Imaging studies of the attentional blink, an effect where conscious awareness of the stimulus is suppressed through reduction of attentional resources, has tended to show the opposite neural response. This study examines changes in stimulus parameters such that either attention or perceptual information is limited. Findings show that under conditions of limited attention but reduced perception the BOLD response reveals increased activity when the stimulus cannot be reported; however, under conditions of reduced perception but normal attention, more activity is revealed on trials when the stimulus can be reported.     

Ipsilateral neglect versus hemianopic compensation

Hemianopic patients may make line bisection errors in the direction of contralesional space, which could represent functional compensation or might be due to ipsilateral neglect. The authors report a patient with stroke with left homonymous hemianopsia and contralesional (leftward) bias on the line bisection task while upright, lying on his left side, and sitting with head bent 90 degrees leftward. Because hemianopic compensation should map retinotopically and the patient consistently erred body-leftward, the authors conclude that his contralesional errors are consistent with ipsilateral neglect.     

Adaptation to cyclic stance perturbations in Parkinson's disease depends on postural demands

The postural reactions of 10 moderate PD patients and 10 age matched controls were studied during stance on a sinusoidally back and forth moving platform during 5 blocks of 10, 1-min trials. Free stance was followed by weight bearing, lowering or raising the center of gravity (COG) by 10%. Next, a book was balanced on the head and finally, forward inclination was constrained. Normal stance strategy, including predictive muscle responses was found during free stance. Modifying COG height caused little response changes. Stance strategy became abnormal when head trajectory or forward inclination was restricted, indicating that ability to generate a nonstandard multi-joint stance strategy, rather than production of adequate stabilizing forces, is impaired in moderate, medicated PD patients.     

Seeing fearful body language overcomes attentional deficits in patients with neglect

Survival depends to some extent on the ability to detect salient signals and prepare an appropriate response even when attention is engaged elsewhere. Fearful body language is a salient signal of imminent danger, easily observable from a distance and indicating to the observer which adaptive action to prepare for. Here we investigated for the first time whether fearful body language modulates the spatial distribution of attention and enhances visual awareness in neurological patients with severe attentional disorders. Patients with visual extinction and hemispatial neglect following right parietal injury have a rightward attentional bias accompanied by loss of awareness for contralesional left stimuli, especially when competing stimuli appear to the right. Three such patients were tested with pictures of fearful, happy, and neutral bodily expressions briefly presented either unilaterally in the left or right visual field, or to both fields simultaneously. On bilateral trials, unattended and task-irrelevant fearful bodily expressions modulated attentional selection and visual awareness. Fearful bodily expressions presented in the contralesional unattended visual field simultaneously with neutral bodies in the ipsilesional field were detected more often than left-side neutral or happy bodies. This demonstrates that despite pathological inattention and parietal damage, emotion and action-related information in fearful body language may be extracted automatically, biasing attentional selection and visual awareness. Our findings open new perspectives on the role of bodily expressions in attentional selection and suggest that a neural network in intact fronto-limbic and visual areas may still mediate reorienting of attention and preparation for action upon perceiving fear in others.