The zero effect: voxel-based lesion symptom mapping of number transcoding errors following stroke

Zero represents a special case in our numerical system because it is not represented on a semantic level. Former research has shown that this can lead to specific impairments when transcoding numerals from dictation to written digits. Even though, number processing is considered to be dominated by the left hemisphere, studies have indicated that both left as well as right hemispheric stroke patients commit errors when transcoding numerals including zeros. Here, for the first time, a large sample of subacute stroke patients (N = 667) was assessed without being preselected based on the location of their lesion, or a specific impairment in transcoding zero. The results show that specific errors in transcoding zeros were common (prevalence = 14.2%) and a voxel-based lesion symptom mapping analysis (n = 153) revealed these to be related to lesions in and around the right putamen. In line with former research, the present study argues that the widespread brain network for number processing also includes subcortical regions, like the putamen with connections to the insular cortex. These play a crucial role in auditory perception as well as attention. If these areas are lesioned, number processing tasks with higher attentional and working memory loads, like transcoding zeros, can be impaired

SPEKTRALANALYTISCHE AUSWERTUNG SPANNUNGSOPTISCHER BILDER

Two hypotheses have been proposed about the etiology of neurodevelopmental learning disorders, such as dyslexia and dyscalculia: representation impairments and disrupted access to representations. We implemented a multi-method brain imaging approach to directly investigate these representation and access hypotheses in dyscalculia, a highly prevalent but understudied neurodevelopmental disorder in learning to calculate. We combined several magnetic resonance imaging methods and analyses, including univariate and multivariate analyses, functional and structural connectivity. Our sample comprised 24 adults with dyscalculia and 24 carefully matched controls. Results showed a clear deficit in the non-symbolic magnitude representations in parietal, temporal and frontal regions, as well as hyper-connectivity in visual brain regions in adults with dyscalculia. Dyscalculia in adults was thereby related to both impaired number representations and altered connectivity in the brain. We conclude that dyscalculia is related to impaired number representations as well as altered access to these representations.ISSN:1053-8119ISSN:1095-957

Spatial attention deficits in humans: The critical role of superior compared to inferior parietal lesions

According to a longstanding view, inferior as opposed to superior parietal cortex critically contributes to the spatial attentional deficits encountered following unilateral parietal ischemic lesions. We review the evidence on which this view is based and contrast it with more recent structural lesion evidence concerning the critical role of the intraparietal sulcus in spatial attention deficits. In a classical spatial cueing paradigm, focal lesions of the posterior and of the middle segment of the intraparietal sulcus give rise to a pathological invalidity effect that is indistinguishable from that seen after classical inferior parietal lesions. When a competing distracter is added to a target stimulus, the deleterious consequences of focal IPS lesions are again very similar to those classically observed following inferior parietal lesions. The deficit could not be accounted for by functional effects at a distance affecting inferior parietal cortex. These single-case lesion data establish the critical role of the posterior and the middle IPS segment in spatially selective attention and are in line with a vast amount of functional imaging evidence in the intact brain pointing to the prominent role of the intraparietal sulcus in spatial attention, along with inferior parietal cortex under specific circumstances. Functional imaging has also provided hints about the differences in functional contribution between inferior and superior parietal cortex. These hypotheses await further confirmation based on lesion evidence

Estimated cut-off scores

This dataset contains files with estimated cut-off scores on the basis of simulated null distributions of two measures of cancellation performance. The cut-off scores were generated through 3 different methods.<br

Test-retest stability

These data contain the distance between a first and second simulated measure of cancellation performance based on constant input parameters. The model used to generate the data is a simple probabilistic step function.<br

Non-spatial impairments affect false positive neglect diagnosis based on cancellation tasks

Objective. To diagnose egocentric neglect after stroke, the spatial bias of performance on cancellation tasks is typically compared to a single cut-off. This standard procedure relies on the assumption that the measurement error of cancellation performance does not depend on non-spatial impairments affecting the total number of cancelled targets. Here we assessed the impact of this assumption on false positive diagnoses. Method. We estimated false positives by simulating cancellation data using a binomial model. Performance was summarized by the difference in left and right cancelled targets (R-L) and the Centre of Cancellation (CoC). Diagnosis was based on a fixed cut-off versus cut-offs adjusted for the total number of cancelled targets, and on single test performance versus unanimous or proportional agreement across multiple tests. Finally, we compared the simulation findings to empirical cancellation data acquired from 651 stroke patients. Results. Using a fixed cut-off, the rate of false positives depended on the total number of cancelled targets, and ranged from 10 to 30% for R-L scores and from 10 to 90% for CoC scores. The rate of false positives increased even further when diagnosis was based on proportional agreement across multiple tests. Adjusted cut-offs and unanimous agreement across multiple tests were effective at controlling false positives. For empirical data, fixed versus adjusted cut-offs differ in estimation of neglect prevalence by 13%, and this difference was largest for patients with non-spatial impairments. Conclusions. Our findings demonstrate the importance of considering non-spatial impairments when diagnosing neglect based on cancellation performance.status: publishe

Neural Correlates of Drug-Related Attentional Bias in Heroin Dependence

The attention of drug-dependent persons tends to be captured by stimuli associated with drug consumption. This involuntary cognitive process is considered as attentional bias (AB). AB has been hypothesized to have causal effects on drug abuse and drug relapse, but its underlying neural mechanisms are still unclear. This study investigated the neural basis of AB in abstinent heroin addicts (AHAs), combining event-related potential (ERP) analysis and source localization techniques. Electroencephalography data were collected in 21 abstinent heroin addicts and 24 age-and gender-matched healthy controls (HCs) during a dot-probe task. In the task, a pair of drug-related image and neutral image was presented randomly in left and right side of the cross fixation, followed by a dot probe replacing one of the images. Behaviorally, AHAs had shorter reaction times (RTs) for the congruent condition compared to the incongruent condition, whereas this was not the case in the HCs. This finding demonstrated the presence of AB towards drug cues in AHAs. Furthermore, the image-evoked ERPs in AHAs had significant shorter P1 latency compared to HCs, as well as larger N1, N2, and P2 amplitude, suggesting that drug-related stimuli might capture attention early and overall require more attentional resources in AHAs. The target-related P3 had significantly shorter latency and lower amplitude in the congruent than incongruent condition in AHAs compared to HCs. Moreover, source localization of ERP components revealed increased activity for AHAs as compared to HCs in the dorsal posterior cingulate cortex (dPCC), superior parietal lobule and inferior frontal gyrus (IFG) for image-elicited responses, and decreased activity in the occipital and the medial parietal lobes for target-elicited responses. Overall, the results of our study confirmed that AHAs may exhibit AB in drug-related contexts, and suggested that the bias might be related to an abnormal neural activity, both in early and late attention processing stages.</p

Spatial stimulus configuration and attentional selection: Extrastriate and superior parietal interactions

The intraparietal sulcus (IPS) is critical for resolving stimulus competition. Its activity is modulated depending on how competing stimuli are spatially configured. Lesions extending into IPS lead to selection deficits when stimuli are configured along a horizontal relative to a vertical or diagonal axis. Using functional magnetic resonance imaging, we examined whether the effect of configuration axis originates at the level of the sensory map in early visual cortex or at the level of the attentional priority map in IPS. In each trial, we presented 1 or 2 peripheral gratings in the upper right visual field and a central letter stream. Subjects performed either a peripheral orientation discrimination task or a central letter detection task. Left IPS activity was higher when peripheral stimuli were configured along the horizontal relative to the vertical axis, but only in peripheral attention conditions. The portions of extrastriate cortex that responded to the peripheral stimuli showed a similar interaction. Connectivity from superior parietal to extrastriate cortex was enhanced by adding a competing distracter during the peripheral attention task. The effect of the spatial configuration between competing stimuli originates at the level of the attentional priority map in IPS rather than the visual sensory map.status: publishe

Lesion neuroanatomy of the Sustained Attention to Response task

The Sustained Attention to Response task is a classical neuropsychological test that has been used by many centres to characterize the attentional deficits in traumatic brain injury, ADHD, autism and other disorders. During the SART a random series of digits 1-9 is presented repeatedly and subjects have to respond to each digit (go trial) except the digit '3' (no-go trial). Using voxel-based lesion symptom mapping (VLSM) in a consecutive series of 44 ischemic unifocal non-lacunar hemispheric stroke patients we determined the neuroanatomy of 4 SART parameters: commission and omission error rate, reaction time variability and post-error slowing. Lesions of the right inferior frontal gyrus significantly increased commission error rate. Lesions of the middle third of the right inferior frontal sulcus (IFS) reduced post-error slowing, a measure of how well subjects can utilize errors to adjust cognitive resource allocation. Omissions and reaction time variability had less localising value in our sample. To conclude, commission errors and post-error slowing in the SART mainly probe right inferior frontal integrity