Damage to the right superior longitudinal fasciculus in the inferior parietal lobe plays a role in spatial neglect

Functional neurological changes after surgery combined with data from diffusion tensor imaging (DTI) studies can provide direct evidence of anatomical localization of brain function. The goal of the present study was to characterize mechanisms of spatial neglect using these techniques by analyzing two patients with development or worsening of left neglect after surgery at our hospital in 2008. In both cases, the surgical approach was via the right inferior parietal lobes, and damage to the superior longitudinal fasciculus (SLF) was demonstrated after surgery by DTI tractography. By contrast, neither the inferior longitudinal fasciculus (ILF) nor the inferior fronto-occipital fasciculus (IFOF) was damaged. These results suggest that damage to the right SLF in the inferior parietal lobe plays a critical role in the development of spatial neglect.     

Left of what? The role of egocentric coordinates in neglect

OBJECTIVES—Egocentric coordinate systems centredon the trunk, head, and gaze have been investigated in a patient whodisplays severe extrapersonal neglect and in five control subjects.
METHODS—The subjects were tested with a blindtactile exploration task in five different experimental conditions inwhich the role of the three distinct frames of reference wasindividually controlled.
RESULTS—Only the trunk centred coordinatessignificantly influenced the performance of the patient, thereforeproving of paramount importance in determining the boundaries of theneglected field. Similar results emerged from a single word readingtask, in which the patient's performance improved when the stimuliwere presented to the right of his body's midline.
CONCLUSION—These findings point to the importanceof the body centred coordinate system in determining the area ofextrapersonal spatial neglect.

     

Sustained attention is associated with right superior longitudinal fasciculus and superior parietal white matter microstructure in children

Sustained attention develops during childhood and has been linked to the right fronto‐parietal cortices in functional imaging studies; however, less is known about its relation to white matter (WM) characteristics. Here we investigated whether the microstructure of the WM underlying and connecting the right fronto‐parietal cortices was associated with sustained attention performance in a group of 76 typically developing children aged 7–13 years. Sustained attention was assessed using a rapid visual information processing paradigm. The two behavioral measures of interest were the sensitivity index d′ and the coefficient of variation in reaction times (RT_CV). Diffusion‐weighted imaging was performed. Mean fractional anisotropy (FA) was extracted from the WM underlying right dorsolateral prefrontal (DLPFC) and parietal cortex (PC), and the right superior longitudinal fasciculus (SLF), as well as equivalent anatomical regions‐of‐interest (ROIs) in the left hemisphere and mean global WM FA. When analyzed collectively, right hemisphere ROIs FA was significantly associated with d′ independently of age. Follow‐up analyses revealed that only FA of right SLF and the superior part of the right PC contributed significantly to this association. RT_CV was significantly associated with right superior PC FA, but not with right SLF FA. Observed associations remained significant after controlling for FA of equivalent left hemisphere ROIs or global mean FA. In conclusion, better sustained attention performance was associated with higher FA of WM in regions connecting right frontal and parietal cortices. Further studies are needed to clarify to which extent these associations are driven by maturational processes, stable characteristics and/or experience. Hum Brain Mapp 34:3216–3232, 2013. © 2012 Wiley Periodicals, Inc.     

The egocentric reference deviation of neglect patients is influenced by visuospatial attention

The right deviation of the subjective straight-ahead (SSA), representing a deviation of the body centered spatial reference frame (egocentric reference), is a frequent phenomenon in spatial neglect. Little is known about the influence of visuo-spatial attention on this SSA shift. The aim of this study was to investigate the influence of eye direction (overt attention) and perception of the visual background (covert attention) on the SSA pointing. We included 12 patients with right hemisphere stroke. Six were classified as neglect (N+) and compared to the six non neglect (N-) patients and 19 normal control subjects (C). They had to point straight-ahead (right hand) on an horizontal board. Pointing was performed in the light or in darkness, first with spontaneous eye direction, then while fixating a visual target (-15 degrees , 0 degrees , +15 degrees ). A first ANOVA of factors group, eye direction (left, center, right fixation) and visual context (light, darkness) showed a right SSA deviation in N+ patients only, which was more severe in the light than in darkness. In this group, the SSA was shifted in the same direction as the target, while that of N- and C groups was mildly shifted in the opposite direction. The comparison of spontaneous and central fixation conditions also showed an eye direction by group interaction, as the spontaneous right SSA deviation was reduced by central fixation in N+ patients only. These results suggest that, in neglect patients, the egocentric reference deviation is not a fixed phenomenon, and that it can be influenced by manipulation of both overt and covert spatial attention.     

Injury of the superior longitudinal fasciculus by ventriculoperitoneal shunt:a diffusion tensor tractography study

正In this study,we report on a patient who suffered from injury of the superior longitudinal fasciculus following ventriculoperitoneal(VP)shunt operation,which was demonstrated with diffusion tensor tractography(DTT).An 82-year-old female patient was diagnosed as suffering from normal pressure hydrocephalus(NPH)and underwent VP shunt operation approached through     

White matter microstructure in superior longitudinal fasciculus associated with spatial working memory performance in children

During childhood and adolescence, ongoing white matter maturation in the fronto-parietal cortices and connecting fiber tracts is measurable with diffusion-weighted imaging. Important questions remain, however, about the links between these changes and developing cognitive functions. Spatial working memory (SWM) performance improves significantly throughout the childhood years, and several lines of evidence implicate the left fronto-parietal cortices and connecting fiber tracts in SWM processing. Here we report results from a study of 76 typically developing children, 7 to 13 years of age. We hypothesized that better SWM performance would be associated with increased fractional anisotropy (FA) in a left fronto-parietal network composed of the superior longitudinal fasciculus (SLF), the regional white matter underlying the dorsolateral pFC, and the posterior parietal cortex. As hypothesized, we observed a significant association between higher FA in the left fronto-parietal network and better SWM skills, and the effect was independent of age. This association was mainly accounted for by variability in left SLF FA and remained significant when FA measures from global fiber tracts or right SLF were included in the model. Further, the effect of FA in left SLF appeared to be mediated primarily by decreasing perpendicular diffusivity. Such associations could be related to individual differences among children in the architecture of fronto-parietal connections and/or to differences in the pace of fiber tract development. Further studies are needed to determine the contributions of intrinsic and experiential factors to the development of functionally significant individual differences in fiber tract structure.     

Lower white matter microstructure in the superior longitudinal fasciculus is associated with increased response time variability in adults with attention-deficit/hyperactivity disorder

Background

Response time variability (RTV) is consistently increased in patients with attention-deficit/hyperactivity disorder (ADHD). A right-hemispheric frontoparietal attention network model has been implicated in these patients. The 3 main connecting fibre tracts in this network, the superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus (ILF) and the cingulum bundle (CB), show microstructural abnormalities in patients with ADHD. We hypothesized that the microstructural integrity of the 3 white matter tracts of this network are associated with ADHD and RTV.

Methods

We examined RTV in adults with ADHD by modelling the reaction time distribution as an exponentially modified Gaussian (ex-Gaussian) function with the parameters μ, σ and τ, the latter of which has been attributed to lapses of attention. We assessed adults with ADHD and healthy controls using a sustained attention task. Diffusion tensor imaging–derived fractional anisotropy (FA) values were determined to quantify bilateral microstructural integrity of the tracts of interest.

Results

We included 100 adults with ADHD and 96 controls in our study. Increased τ was associated with ADHD diagnosis and was linked to symptoms of inattention. An inverse correlation of τ with mean FA was seen in the right SLF of patients with ADHD, but no direct association between the mean FA of the 6 regions of interest with ADHD could be observed.

Limitations

Regions of interest were defined a priori based on the attentional network model for ADHD and thus we might have missed effects in other networks.

Conclusion

This study suggests that reduced microstructural integrity of the right SLF is associated with elevated τ in patients with ADHD.     

Tract-specific analysis of the superior occipitofrontal fasciculus in schizophrenia

Diffusion tensor imaging has been highlighted as a non-invasive tool to explore neural connectivity in vivo. Several studies have suggested disorganization of the neural network (circuitry) including the thalamo-prefrontal connection in schizophrenia. Recent research using post-mortem brains showed that the superior occipitofrontal fasciculus (SOFF) fibers extended to the thalamus. We postulated that the SOFF has some relationship with the anatomical structural components of the thalamo-prefrontal circuitry. We quantitatively assessed the diffusion abnormalities of the SOFF using diffusion tensor tractography (DTT) in schizophrenia. Nineteen male patients with schizophrenia and 20 age-matched normal controls were studied. DTT of the SOFF (DTT-SOFF) was visualized using free software (dTV II/VOLUME-ONE), and we performed tract-specific measurement of the fractional anisotropy (FA), then calculated the apparent diffusion coefficient (ADC) of the DTT-SOFF. Tractography and tract-specific analysis of the SOFF were successfully performed in all subjects. All tracts appeared to be connecting the prefrontal area to the thalamus. The mean FA value of patients with schizophrenia [0.376 (S.D. 0.030)] was significantly lower than that of controls [0.432 (S.D. 0.032)], and the ADC value of patients with schizophrenia [0.771 (× 10^− 3 mm²/s) (S.D. 0.041)] was significantly higher than that of controls [0.726 (× 10^− 3 mm²/s) (S.D. 0.027)]. Our results suggest that the so-called SOFF may be a structural component connecting the prefrontal area to the thalamus and that it is deteriorated in schizophrenia.     

Hemispatial neglect in young children with early unilateral brain damage

Hemispatial neglect is commonly observed in adults following right-hemisphere brain lesions. Given the potential for reorganization in the developing brain, spatial neglect may not be apparent following early unilateral damage. This study aimed to determine whether infants who experienced pre- or perinatal focal brain lesions showed evidence of spatial neglect. Study participants were 33 infants/toddlers (22 males, 11 females; age range 6 to 48 months); 27 preschool children (14 males, 13 females; age range 28 to 75 months) with either left hemisphere (LH) or right hemisphere (RH) damage of pre- or perinatal onset (total 60), and 36 control individuals (15 females, 21 males; age range 28 to 75 months). Participants were assessed using two object-removal preference tasks. Control children showed no lateralized preference for object removal. Those with LH or RH damage preferentially removed objects from the side of the board ipsilateral to the lesion first and the contralateral side last. These results suggest that spatial neglect may be found in young children even after very early unilateral brain damage. Further, in contrast to the adult pattern, contralateral neglect is present for up to 6 years after either LH or RH damage. This pattern suggests that there may be a different distribution of attention to space in the developing brain as compared with the mature brain. The persistence of spatial neglect suggests that there are some limitations on plasticity in the developing human brain.     

Inhibitory control is slowed in patients with right superior medial frontal damage

Inhibitory control is an essential part of behavior. Comprehensive knowledge of the neural underpinnings will shed light on complex behavior, its breakdown in neurological and psychological disorders, and current and future techniques for the pharmacological or structural remediation of disinhibition. This study investigated the neural mechanisms involved in rapid response inhibition. The stop signal task was used to estimate inhibitory speed in a group of neurologically normal control subjects and patients with discrete frontal lobe lesions. Task procedures were controlled to rule out probable confounds related to strategic changes in task effort. The findings indicate that the frontal lobes are necessary for inhibitory control and, furthermore, that the integrity of the right superior medial frontal region is key for rapid inhibitory control under conditions controlling for strategically slow responses, forcing reliance more on a rapid, "kill-switch" inhibitory system. These results are interpreted within an anatomical framework of corticospinal motor control.     

Visuospatial asymmetry and non-spatial attention in subacute stroke patients with and without neglect

Asymmetry in performance and an association with non-lateralized attention are often mentioned as two important aspects of the clinical manifestation of visuospatial neglect. Both these aspects were investigated in 21 left (LH) and 24 right hemisphere (RH) stroke patients and in 20 healthy subjects. The letter and star cancellation subtests of the Behavioural Inattention Task (BIT) and a computerized visual reaction time task (CVRT) with stimuli presented either left, central or right in extrapersonal space were administered. In LH patients, the calculation of BIT asymmetry scores allowed a better distinction between patients with and without neglect than raw omission scores. However, in RH patients, raw and asymmetry scores led to similar classifications. In the CVRT, raw and asymmetry scores for the number of omissions also produced identical classifications. Thus, the computation of asymmetry scores for omissions did not substantially refine the diagnosis of neglect. On the other hand, more patients were classified as neglect patients by using CVRT reaction time (RT) asymmetry scores than by using BIT or CVRT omission scores. Ipsilesional RT's were chosen as a measure of general, non-lateralized attention. The ipsilesional RT's of the LH and RH patients did not differ from the healthy subjects' lateral RT's. However, within the RH group, patients with both RT asymmetries and BIT scores above cut-off level showed longer ipsilesional RT's than patients with defective RT asymmetries but normal BIT scores. This supports the idea of an interaction between lateralized and non-lateralized attentional components in neglect, in which the presence of general attentional deficits exacerbates the severity of neglect symptoms. RT tasks may contribute to the detection of asymmetries in visuospatial attention in patients with subclinical neglect symptoms, who might compensate for their lateralized deficit in paper-and-pencil tasks employing intact general attention.     

Cell groups of the medial longitudinal fasciculus and paramedian tracts

The aim of this article is to introduce the reader to a continuum of cell clusters which may play an important role in the maintenance of eye position. They lie interspersed between the fascicles of the medial longitudinal fasciculus (MLF) and paramedian tracts in the caudal pons and medulla, and they also constitute the rostral part of the classical abducens nucleus. Previous workers showed that these 'cell groups of the paramedian tracts' (pmt cell groups) project to the flocculus, and receive afferents from several horizontal premotor cell groups. Results of neuroanatomical tracer experiments reported here demonstrate that they also receive a direct input from the vertical premotor gaze neurons in the mesencephalon (rostral iMLF and the interstitial nucleus of Cajal), as well as from some groups of oculomotor internuclear neurons. The projecting fibres descend to the cell groups of the paramedian tracts in the MLF. It is suggested that deficits in gaze-holding seen in internuclear ophthalmoplegia, for example, may result from damage to afferents of this paramedian cell continuum.     

Time course of visuospatial neglect early after stroke: A longitudinal cohort study

The aim of the current study was to investigate recovery of visuospatial neglect during the first year after stroke. Visuospatial neglect was measured using two frequently and widely used tests: the letter cancellation test (LCT) and the line bisection test (LBT). This was a prospective cohort study of 101 stroke patients. Of these 101 patients, 51 patients showed visuospatial neglect. All time-dependent measures were taken weekly, starting from within 14 days after stroke onset. From week 10–20 biweekly measurements were obtained. Follow-up measurements were performed at weeks 26, 38, and finally 52. For the present study, number of misses in the LCT, split on contralesional versus ipsilesional side, as well as the deviation from the actual midpoint in mm in the LBT were used. The longitudinal relationship of (bi)weekly time on improvement in LBT and LCT were investigated using random coefficient analysis and joinpoint analyses. Results indicated that progress of time is an independent covariate that reflects neurological recovery of visuospatial neglect. Additionally, trend changes were obtained in between 12 and 14 weeks post-stroke with respect to the neglected side. This is the first prospective cohort study in which the time course of neglect is investigated by using intensive serial measurements in the early months post-stroke.