Attentional modulation of parieto-occipital cortical responses: implications for hemispatial neglect

Functional magnetic resonance imaging (fMRI) was used to examine whether preattentive and attentive visual processing, the cognitive psychological dichotomy on normal vision, indeed activate the parieto-occipital systems differentially as suggested by recent neuropsychological research. The activation paradigms consisted of feature detection and discrimination of line orientation, and visual fixation, which corresponded to preattentive, attention-requiring, and baseline conditions, respectively. The detection versus fixation contrast revealed activation sites in the right lateral prefrontal cortex and bilateral occipital lobes, whereas the discrimination versus fixation contrast showed broader bilateral activations extending from the occipital lobes through the parietal lobes, prefrontal cortex, thalamus, basal ganglia and upper brainstem. In the discrimination versus detection contrast, significant activations were observed in the right superior and inferior parietal lobules as well as in the subcortical structures. These findings were consistently demonstrated both at intra- and inter-subject levels. The present study provides further evidence to delineate neural substrate for the two distinct modes of visual processing and helps us to understand the neuropsychological mechanism underlying visual attention disorders.     

Line quadrisection errors in patients with hemispatial neglect

Patients with left unilateral neglect misbisect lines toward the right. To discriminate between contralesional unawareness and ipsilesional hyperattention hypotheses for this ipsilesional bias, we performed the line quadrisection test on 18 patients with and 25 without neglect, and 24 normal controls. Overall the patients with neglect were unbiased when performing the left quadrisection task, but erred rightward on the right quadrisection task. These results suggest that the ipsilesional bisection errors produced by patients with neglect are primarily influenced by ipsilesional hyperattention rather than contralesional unawareness. However, further analyses showed heterogeneity of performance in left quadrisection, which can be explained by multiple factors that include the top down attention to left space associated with left quadrisection, the orienting to the salience of the line's left end, and distorted mental representation, in addition to ipsilesional hyperattention.     

Line quadrisection errors in patients with hemispatial neglect

Patients with left unilateral neglect misbisect lines toward the right. To discriminate between contralesional unawareness and ipsilesional hyperattention hypotheses for this ipsilesional bias, we performed the line quadrisection test on 18 patients with and 25 without neglect, and 24 normal controls. Overall the patients with neglect were unbiased when performing the left quadrisection task, but erred rightward on the right quadrisection task. These results suggest that the ipsilesional bisection errors produced by patients with neglect are primarily influenced by ipsilesional hyperattention rather than contralesional unawareness. However, further analyses showed heterogeneity of performance in left quadrisection, which can be explained by multiple factors that include the top down attention to left space associated with left quadrisection, the orienting to the salience of the line's left end, and distorted mental representation, in addition to ipsilesional hyperattention.     

Non-lateralised deficits in anti-saccade performance in patients with hemispatial neglect

We tested patients suffering from hemispatial neglect on the anti-saccade paradigm to assess voluntary control of saccades. In this task participants are required to saccade away from an abrupt onset target. As has been previously reported, in the pro-saccade condition neglect patients showed increased latencies towards targets presented on the left and their accuracy was reduced as a result of greater undershoot. To our surprise though, in the anti-saccade condition, we found strong bilateral effects: the neglect patients produced large numbers of erroneous pro-saccades to both left and right stimuli. This deficit in voluntary control was present even in patients whose lesions spared the frontal lobes. These results suggest that the voluntary control of action is supported by an integrated network of cortical regions, including more posterior areas. Damage to one or more components within this network may result in impaired voluntary control.     

Bilateral impairment of concurrent saccade programming in hemispatial neglect

When healthy observers make a saccade that is erroneously directed toward a distracter stimulus, they often produce a corrective saccade within 100 ms after the end of the primary saccade. Such short inter-saccadic intervals indicate that programming of the secondary saccade has been initiated prior to the execution of the primary saccade and hence that the two saccades have been programmed concurrently. Here we show that concurrent saccade programming is bilaterally impaired in left spatial neglect, a strongly lateralized disorder of visual attention resulting from extensive right cerebral damage. Neglect patients were asked to make saccades to targets presented left or right of fixation while disregarding a distracter presented in the opposite hemifield. We examined those experimental trials on which participants first made a saccade to the distracter, followed by a secondary (corrective) saccade to the target. Compared to healthy and right-hemisphere damaged control participants the proportion of secondary saccades directing gaze to the target instead of bringing it even closer to the distracter was bilaterally reduced in neglect patients. In addition, the characteristic reduction of secondary saccade latency observed in both control groups was absent in neglect patients, whether the secondary saccade was directed to the left or right hemifield. This pattern is consistent with a severe, bilateral impairment of concurrent saccade programming in left spatial neglect.     

The neural basis of visuomotor deficits in hemispatial neglect

We have recently reported that patients with hemispatial neglect demonstrate increased terminal errors when performing delayed leftward reaches and that right-brain damaged patients (irrespective of neglect) take longer to complete their movements [Rossit, S., Muir, K., Reeves, I., Duncan, G., Birschel, P., & Harvey, M. (2009). Immediate and delayed reaching in hemispatial neglect. Neuropsychologiaa 47, 1563-1573]. Here we conducted an initial voxel-based lesion-symptom analysis to examine the neural basis of such deficits in 21 right-brain damaged subjects with 11 patients suffering from hemispatial neglect (2 more than in Rossit et al. [Rossit S., Muir K., Reeves I., Duncan, G., Birschel, P., & Harvey, M. (2009). Immediate and delayed reaching in hemispatial neglect. Neuropsychologia 47, 1563-1573] and 10 control patients without the condition. We found that the accuracy impairments in delayed leftward reaches were associated with damage to occipito-temporal areas. In contrast, the movement time slowing was related to more anterior lesions in the frontal lobe. These findings agree with the view that neglect affects actions thought to depend on the processing carried out by the ventral visual stream. In addition, we suggest that the timing impairments which are not neglect-specific maybe be driven by frontal structures.     

Evidence for distinct beta resonance frequencies in human EEG related to specific sensorimotor cortical areas.

OBJECTIVE: We studied event-related synchronization (ERS) of beta rhythms related to voluntary movement vs. stimulation of upper and lower limbs. The aim of this study was to investigate whether the frequency of the beta response is related to specific regions within the sensorimotor strip. METHODS: Self-paced movement and electrical stimulation of the dominant hand and foot/leg was investigated in 10 right-handed volunteers. The electroencephalogram was recorded from closely spaced electrodes over central areas and processed time-locked to movement-offset or stimulation. In order to identify the dominant frequency of the induced beta oscillations, time-frequency maps were calculated using the continuous wavelet transformation. For the specific beta frequency bands, the band power time courses were analyzed by quantifying the event-related (de-)synchronization (ERD/ERS). RESULTS: Both limb movement and somatosensory stimulation induced bursts of beta oscillations appearing within 1 s after movement/stimulation with a clear focus close to the corresponding sensorimotor representation area. The peak frequency was significantly lower over the hand area (below approximately 20 Hz) than at mid-central sites overlying the foot representation area (above approximately 20 Hz). But no difference was found between movement and stimulation of the respective limb. CONCLUSIONS: Analyzing the frequency of induced beta activity revealed concomitant oscillations at slightly different frequencies over neighboring cortical areas. These oscillations might be indicative for a resonance-like behavior of connected sub-networks in sensorimotor areas.     

Brief International Cognitive Assessment for Multiple Sclerosis scores are associated with the cortical thickness of specific cortical areas in relapsing-remitting patients

BackgroundCognitive impairment is frequent and disabling in multiple sclerosis (MS). The Brief International Cognitive Assessment in MS (BICAMS) is a recent short battery usable in clinical practice for cognitive evaluation of MS patients.ObjectiveTo find cortical areas or brain volumes on magnetic resonance imaging (MRI) structural sequences associated with BICAMS scores in MS.MethodsIn this cross-sectional single-center study (NCT 03656055, September 4, 2018), 96 relapsing remitting-MS patients under natalizumab and without recent clinical or radiological inflammation were included. Patients underwent brain MRI and the three BICAMS tests, evaluating information processing speed (SDMT), visuo-spatial memory (BVMT-R), and verbal memory (FVLT).ResultsCortical thickness in the left frontal superior and the right precentral gyri was associated with BVMT-R scores whereas cortical thickness in the left Broca's area and the right superior temporal gyrus was associated with FVLT scores. We observed associations between white matter inflammatory lesions connected to these cortical regions and BICAMS subscores.ConclusionsBICAMS scores are associated with specific cortical areas, the cognitive domain matching the known functions of the cortical area. Specific cognitive impairments in MS may be associated with specific cortical regions, themselves influenced by white matter inflammatory lesions and demographical parameters (age, sex, education level).     

Left hemispatial visual neglect associated with a combined right occipital and splenial lesion: another disconnection syndrome

Damage to the left occipital lobe and the splenium or forceps major is often associated with pure alexia, thought to be an occipital-temporoparietal disconnection syndrome. A patient with the parallel lesion, a combined right occipital and splenial lesion, showed severe left-sided visual spatial neglect, but no significant neglect in other sensory modalities. This visual neglect might be related to a disconnection between the visual information processed by the left occipital lobe and the right posterior temporal-inferior parietal areas that mediate attention in the left hemispace.     

Postictal but not interictal hemispatial neglect in patients with seizures of lateralized onset

PURPOSE: Unilateral spatial neglect, defined as a failure to report, respond, or orient to stimuli that are presented contralaterally, has been widely documented after brain damage to right, and to a lesser degree, left frontotemporoparietal networks. Group studies involving patients with seizures with a lateralized focus have demonstrated transient dysfunctions in memory and language; however, so far, only two case reports have described transient neglect after an epileptic seizure. METHODS: To assess the existence and consistency of this phenomenon, we evaluated 33 epilepsy patients on a line-bisection task in interictal and postictal states as compared with an age- and sex-matched control group. RESULTS: Spatial neglect, as determined by this test, was found in the postictal but not interictal examination in patients with right parietal epileptic foci and was maximal for the left-positioned lines, whereas no neglect was found in other groups. CONCLUSIONS: Our findings indicate that patients with right parietal foci can present a transient neglect phenomenon on the line-bisection task in the postictal period, even in the absence of overt clinical neglect signs. These findings might be useful in establishing the laterality and even localization of epileptic foci based on the postictal neuropsychological evaluation.     

Left hemispatial visual neglect associated with a combined right occipital and splenial lesion: Another disconnection syndrome

Damage to the left occipital lobe and the splenium or forceps major is often associated with pure alexia, thought to be an occipital-temporoparietal disconnection syndrome. A patient with the parallel lesion, a combined right occipital and splenial lesion, showed severe left-sided visual spatial neglect, but no significant neglect in other sensory modalities. This visual neglect might be related to a disconnection between the visual information processed by the left occipital lobe and the right posterior temporal-inferior parietal areas that mediate attention in the left hemispace.     

Repetition of distractor sets improves visual search performance in hemispatial neglect

Priming from repeated distractor sets, or search context, in conjunctive visual search was examined in four patients with hemispatial neglect. In the first experiment overall context was either changed or repeated while the target was always the same to control for any modulatory effect of target priming. Considerable priming was seen from repeated context. In the second experiment the context was either repeated on the left side, on the right side, on both sides, or the context was new. Priming from repeated context was found to arise from the left visual field, as well as the right visual field, as well as when overall context was repeated. Brief masked displays were used in experiment 3, the results again showing strong priming from repeated overall context. The results of the three experiments suggest that visual grouping, or perceptual organization, of distractor sets is relatively intact in the affected hemifield of parietal neglect patients. Furthermore, repetition of context may even temporarily ameliorate neglect symptoms in search. These findings are consistent with claims that grouping is distinct from attentional processing and that it operates at lower levels of the perceptual hierarchy.     

Marchiafava-Bignami disease with symptoms of the motor impersistence and unilateral hemispatial neglect

Machiafava-Bignami disease (MBD) occurs in the alcoholic patients. It is characterized clinically by interhemispheric disconnection syndrome, resulting from demyelination and necrosis of the corpus callosum. We performed a neuropsychological study of an alcoholic patient, diagnosed as MBD by X-ray computed tomography (CT) and magnetic resonance imaging (MRI). 123I IMP-SPECT of the patient revealed the reduction of the blood flow in both cerebral hemispheres without laterality though both the X-ray CT and MRI showed no abnormality in the cerebral hemispheres. In neuropsychological studies, we observed not only interhemispheric disconnection syndrome such as an unilateral left agraphia and left apraxia but also left hemispatial neglect demonstrated in right-hand performance and motor impersistence. Because there were no abnormal lesions in the right hemisphere, these symptoms might be attributable to the lesions of corpus callosum.     

线索提示对忽视症患者线等分反转效应的影响

目的 研究线段长度、线索提示对忽视症患者线等分试验中反转效应的影响,以探讨注意、感觉、数量估计障碍等是否参与忽视症患者线等分试验中反转效应的神经机制.方法 试验对象为15例左侧空问忽视症患者和15名年龄、文化程度、MMSE评分等相匹配的健康人,进行不同线段长度和线索提示的线等分试验,观察线等分试验的偏移率和反转效应.健康对照组间分析比较用两独立样本t检验,各组内结果分析采用多因素的方差分析.结果 忽视症患者在单纯水平线等分中当线段长度分别为4、6、8、10、12 cm时,其偏移百分率(%)分别为-5.71±5.13、-2.48±8.83、-1.18±10.90、0.43±8.12、2.17±7.04,线段长度对偏移率影响有统计学意义(F=12.5,P＜0.01).线段长度小于10 cm时,9例表现为反转效应.相应长度线段右、左侧单侧增加线索提示,可削弱和增强忽视症患者线等分试验的反转效应[偏移百分率(%)分别为-3.93±7.04、2.43±6.34、4.93±5.19、6.49±3.36、6.38±4.18,P＜0.01;-10.93±8.85、-7.95±8.44、-4.14±8.37、-2.60±9.96、-1.57±10.67,P=0.03];双侧增加线索提示对反转效应影响无统计学意义[偏移百分率(%)分别为-5.93±7.76、-0.52±8.20、0.54±6.34、2.57±5.02、2.79±3.92,P=0.35].改变线索提示高度对反转效应影响无统计学意义(F=1.94,P=0.14).结论 在线等分试验中当线段长度较短时主观中点向左偏移,表现为反转效应,表明数量估计障碍参与反转效应的形成.在线等分试验中增加单侧线索提示对偏移率影响显著,表明注意导向参与反转效应的形成.改变线索提示高度对反转效应影响无统计学意义,表明感觉障碍在反转效应形成过程中不起独立因素.     

Cerebral blood flow in patients with various symptoms of hemispatial neglect following ischemic stroke

BACKGROUND AND PURPOSE: The most common cause of hemispatial neglect (HN) is cerebral infarction. It can be induced by lesions in many different regions of the right hemisphere. The purpose of this article was to determine the prevalence of post-stroke HN, its clinical picture, and neuroanatomical correlates. MATERIAL AND METHODS: Forty-six stroke patients with a focal right-hemisphere lesion were studied. Neglect in visual domain, assessed with a battery of drawing, line bisection and shape cancellation tests, was observed in 20 cases. The single-photon emission-computed tomography (SPECT) images of the brain were obtained with 740 MBq (20 mCi) of Tc-99m-labeled ECD on a triple-headed gamma camera. RESULTS: The most sensitive measure of HN was the cancellation test, which all neglect patients performed poorly. Twelve patients, classified as mildly impaired, showed no significant rightward deviation on line bisection, but they showed left visual neglect on the cancellation test. Reverse dissociation was not noted. Performance on a clock-drawing test revealed HN only in two patients, who showed also evidence of HN on other tests. Thereby, some of the tests seem to be more difficult or more sensitive to impairment. The critical area of perfusion abnormalities in all neglect patients were frontal lobe and striatum on the right. In severe HN, SPECT images evidenced the most extensive hypoperfusion throughout the perisylvian region and subcortical structures of the right hemisphere. Although parietal cortex was affected in patients with moderate to severe HN, it was spared in the rest. CONCLUSIONS: HN was a relatively common symptom of vascular right-hemisphere damage (43% of the patient population). HN was a complex disturbance in terms of its clinical manifestation and neuroimaging correlates. Our findings challenge the classical notion that damage to the parietal cortex is critically associated with HN. Instead, our results support the model attributing hemispatial neglect to a defect in a cortico-striato-thalamo-cortical loop. Also, the present study highlights the usefulness of cerebral blood flow SPECT imaging as a diagnostic aid in the post-stroke deficits of cognition following right-hemisphere damage.     

Triangular backgrounds shift the bias of line bisection performance in hemispatial neglect

OBJECTIVE: Patients with left neglect on line bisection show normal implicit sensitivity to manipulations of both the stimulus and the visual background. Three experiments were designed to define this sensitivity more exactly. METHODS: Normal controls and patients with left neglect performed a series of horizontal line bisection tasks. Independent variables were the configurations of the backgrounds for the line-rectangle, square, circle, left and right pointing isosceles triangles-and whether the background was the shape of the piece of paper or an outline drawn on a standard piece of paper. In a separate experiment different components of the triangle were outlined on a piece of paper. Deviation from true midpoint was calculated. RESULTS: Simply placing the target lines in a symmetric background such as a square or circle did not reliably reduce neglect. A triangle asymmetric in the horizontal plane caused a shift in bisection away from the triangle's vertex. With right pointing triangles the perceived midpoint shifted to the left of true centre (crossed over). The effects of the triangles were comparable in the patients and the controls when controlled for baseline bisection bias. The critical components of the triangles were the angular legs. This effect of background was not influenced by lesion site or by hemianopia. CONCLUSIONS: Patients with left visual neglect remain sensitive to covert manipulations of the visual background that implicitly shift the perceived midpoint of a horizontal line. This effect is strong enough to eliminate neglect on a bisection task. The mechanism of this effect is expressed through preattentive visual capacities.     

Childhood neglect is associated with reduced corpus callosum area.

BACKGROUND: Childhood abuse has been associated with abnormalities in brain development, particularly corpus callosum (CC) morphology. The impact of neglect has not been assessed, though it is the most prevalent form of childhood maltreatment. METHODS: Regional CC area was measured from magnetic resonance imaging scans in 26 boys and 25 girls admitted for psychiatric evaluation (28 with abuse or neglect) and compared with CC area in 115 healthy control subjects. Data were analyzed by multivariate analysis of covariance, with age and midsagittal area as covariates. RESULTS: Total CC area of the abused/neglected patients was 17% smaller than in control subjects (p =.0001) and 11% smaller than in psychiatric patients who had not been abused or neglected (contrast group; p =.01). Control subjects and the contrast group did not differ in total CC area. Neglect was the strongest experiential factor and was associated with a 15%-18% reduction in CC regions 3, 4, 5, and 7 (all p <.02). In contrast, sexual abuse seemed to be the strongest factor associated with reduced CC size in girls. CONCLUSIONS: These data are consistent with animal research that demonstrated reduced CC size in nursery-reared compared with semi-naturally reared primates. Early experience might also affect the development of the human CC.