Papers by Michal Ben-shachar
The functional anatomy of syntactic transformations, a ma-jor computational operation invoked in ... more The functional anatomy of syntactic transformations, a ma-jor computational operation invoked in sentence processing, was iden-tified through a functional magnetic resonance imaging investigation. A grammaticality judgment task was used, presented through a novel hidden-blocks design. Subjects listened to transformational and non-transformational sentences in which a host of other complexity gener-ators (number of words, prepositions, embeddings, etc.) were kept constant. A series of analyses revealed that the neural processing of transformations is localizable, evoking a highly lateralized and local-ized activation in the left inferior frontal gyrus (Broca’s region) and bilateral activation in the posterior superior temporal sulcus. The pat-tern of activation associated with transformational analysis was dis-tinct from the one observed in neighboring regions, and anatomically separable from the effects of verb complexity, which yielded significant activation in the left posterior s...
Skilled reading requires mapping of visual text to sound and meaning. Because reading relies on n... more Skilled reading requires mapping of visual text to sound and meaning. Because reading relies on neural systems spread across the brain, a full understanding of this cognitive ability involves the identification of pathways that communicate information between these processing regions. In the past few years, diffusion tensor imaging has been used to identify correlations between white matter properties and reading skills in adults and children. White matter differences have been found in left temporo-parietal areas and in posterior callosal tracts. We review these findings and relate them to possible pathways that are important for various aspects of reading. We describe how the results from diffusion tensor imaging can be integrated with functional results in good and poor readers.
Multimodal behavior involves multiple processing stations distributed across distant brain region... more Multimodal behavior involves multiple processing stations distributed across distant brain regions, but our understanding of how such distributed processing is coordinated in the brain is limited. Here we take a decoding approach to this problem, aiming to quantify how temporal aspects of brain-wide neural activity may be used to infer specific multimodal behaviors. Using high temporal resolution measurements by MEG, we detect bursts of activity from hundreds of locations across the surface of the brain at millisecond resolution. We then compare decoding using three characteristics of neural activity bursts, decoding with event counts, with latencies and with time differences between pairs of events. Training decoders in this regime is particularly challenging because the number of samples is smaller by orders of magnitude than the input dimensionality. We develop a new decoding approach for this regime that combines non-parametric modelling with aggressive feature selection. Surpri...
Journal of Communication Disorders
Diffusion magnetic resonance imaging (dMRI) studies find differences in associations between read... more Diffusion magnetic resonance imaging (dMRI) studies find differences in associations between reading and white matter fractional anisotropy (FA) in children born full term (FT) versus preterm (PT). Use of complementary neuroimaging modalities may reveal neurobiological factors driving these associations. We used two MRI methods to interpret associations of reading abilities and white matter properties in FT and PT children. Participants (N=79; 36 FT; 43 PT) were administered Gray’s Oral Reading Test at age 8 years. We segmented two dorsal and two ventral white matter tracts associated with reading skills and quantified (1) FA from dMRI and (2) R1 from quantitative relaxometry, as a proxy for myelin content. We examined correlations between reading scores and imaging metrics, assessing trajectories along the tracts. Mean reading scores fell in the typical range in both groups. Reading positively correlated with FA in segments of the left arcuate and the left and right superior longit...
An accurate model of the factors that contribute to individual differences in reading ability dep... more An accurate model of the factors that contribute to individual differences in reading ability depends on data collection in large, diverse and representative samples of research participants. However, that is rarely feasible due to the constraints imposed by standardized measures of reading ability which require test administration by trained clinicians or researchers. Here we explore whether a simple, two-alternative forced choice, time limited lexical decision task (LDT), self-delivered through the web-browser, can serve as an accurate and reliable measure of reading ability. We found that performance on the LDT is highly correlated with scores on standardized measures of reading ability such as the Woodcock-Johnson Letter Word Identification test (r = 0.91, disattenuated r = 0.94). Importantly, the LDT reading ability measure is highly reliable (r = 0.97). After optimizing the list of words and pseudowords based on item response theory, we found that a short experiment with 76 tr...
The Cerebellum
Reading in children has been associated with microstructural properties of the cerebellar peduncl... more Reading in children has been associated with microstructural properties of the cerebellar peduncles, the white matter pathways connecting the cerebellum to the cerebrum. In this study, we used two independent neuroimaging modalities to assess which features of the cerebellar peduncles would be associated with reading. Twenty-three 8-year-old children were evaluated on word reading efficiency and imaged using diffusion MRI (dMRI) and quantitative T1 relaxometry (qT1). We segmented the superior (SCP), middle, and inferior cerebellar peduncles and extracted two metrics: fractional anisotropy (FA) from dMRI and R1 from qT1. Tract-FA was significantly correlated with tract-R1 in left and right SCPs (left: rP(21) = .63, right: rP(21) = .76, p ≤ .001) suggesting that FA of these peduncles, at least in part, indexed myelin content. Tract-FA and tract R1 were not correlated in the other cerebellar peduncles. Reading efficiency negatively correlated with tract-FA of the left (rP(21) = − .43, p = .040) and right SCP (rP(21) = − .37, p = .079). Reading efficiency did not correlate with tract-R1 in the SCPs. The negative association of reading efficiency with tract-FA and the lack of association of reading efficiency with tract-R1 implicate properties other than myelin content as relevant to the information flow between the cerebellum and the cerebrum for individual differences in reading skills in children.
The Cerebellum
In sensorimotor adaptation paradigms, participants learn to adjust their behavior in response to ... more In sensorimotor adaptation paradigms, participants learn to adjust their behavior in response to an external perturbation. Locomotor adaptation and reaching adaptation depend on the cerebellum and are accompanied by changes in functional connectivity in cortico-cerebellar circuits. In order to gain a better understanding of the particular cerebellar projections involved in locomotor adaptation, we assessed the contribution of specific white matter pathways to the magnitude of locomotor adaptation and to long-term motor adaptation effects (recall and relearning). Diffusion magnetic resonance imaging with deterministic tractography was used to delineate the inferior and superior cerebellar peduncles (ICP, SCP) and the corticospinal tract (CST). Correlations were calculated to assess the association between the diffusivity values along the tracts and behavioral measures of locomotor adaptation. The results point to a significant correlation between the magnitude of adaptation and diffusivity values in the left ICP. Specifically, a higher magnitude of adaptation was associated with higher mean diffusivity and with lower anisotropy values in the left ICP, but not in other pathways. Post hoc analysis revealed that the effect stems from radial, not axial, diffusivity. The magnitude of adaptation was further associated with the degree of ICP lateralization, such that greater adaptation magnitude was correlated with increased rightward asymmetry of the ICP. Our findings suggest that the magnitude of locomotor adaptation depends on afferent signals to the cerebellum, transmitted via the ICP, and point to the contribution of error detection to locomotor adaptation rate.
Cortex
Skilled readers differ in their sensitivity to morphological word structure, which captures usefu... more Skilled readers differ in their sensitivity to morphological word structure, which captures useful regularities in the mapping between written word forms and their meaning. We recently showed that sensitivity to morphological information in adult English readers is associated with the ventral reading pathways, bilaterally. It remains unclear, however, whether this association is specific to the English writing system. To shed light on this question, we investigated whether the associations between the ventral reading pathways and morphological sensitivity to word structure generalize across languages with different orthographies and morphological systems. To this end, we assessed neurocognitive correlations between white matter structural properties and morphological sensitivity in Hebrew, a Semitic language where morphemes are combined in a non-linear manner. We used diffusion MRI (dMRI) to segment ventral and dorsal tracts of interest in a sample of 43 adult Hebrew readers, who also completed a behavioral language assessment battery that included a morphological task. Significant correlations were found between morphological sensitivity and properties of bilateral ventral, but not dorsal, tracts. These correlations remained significant after controlling for measures of vocabulary and word reading, demonstrating their specificity to the morphological task. The current findings in Hebrew show striking similarity to prior findings in English. Our results support the view that morphological information contributes to lexical access along the ventral pathways, across orthographies and morphological systems.
The Mental Lexicon
A growing body of psycholinguistic research suggests that visual and auditory word recognition in... more A growing body of psycholinguistic research suggests that visual and auditory word recognition involve morphological decomposition: Individual morphemes are extracted and lexically accessed when participants are presented with multi-morphemic stimuli. This view is supported by the Morpheme Interference Effect (MIE), where responses to pseudowords that contain real morphemes are slower and less accurate than responses to pseudowords that contain invented morphemes. The MIE was previously demonstrated primarily for visually presented stimuli. Here, we examine whether individuals’ sensitivity to morphological structure generalizes across modalities. Participants performed a lexical decision task on visually and auditorily presented Hebrew stimuli, including pseudowords derived from real or invented roots. The results show robust MIEs in both modalities. We further show that visual MIE is consistently stronger than auditory MIE, both at the group level and at the individual level. Final...
Frontiers in Human Neuroscience
Children born preterm (PT) are at risk for white matter injuries based on complications of premat... more Children born preterm (PT) are at risk for white matter injuries based on complications of prematurity. They learn to read but on average perform below peers born full term (FT). Studies have yet to establish whether properties of white matter pathways at the onset of learning to read are associated with individual variation later in reading development in PT children. Here, we asked whether fractional anisotropy (FA) at age 6 years is associated with reading outcome at age 8 years in PT children in the same pathways as previously demonstrated in a sample of FT children. PT (n = 34, mean gestational age = 29.5 weeks) and FT children (n = 37) completed diffusion MRI and standardized measures of non-verbal IQ, language, and phonological awareness at age 6 years. Reading skills were assessed at age 8 years. Mean tract-FA was extracted from pathways that predicted reading outcome in children born FT: left arcuate fasciculus (Arc), bilateral superior longitudinal fasciculus (SLF), and left inferior cerebellar peduncle (ICP). We explored associations in additional pathways in the PT children: bilateral inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, and uncinate fasciculus. Linear regression models examined whether the prediction of reading outcome at age 8 years based on mean tract-FA at age 6 years was moderated by birth group. Children born PT and FT did not differ significantly in tract-FA at age 6 years or in reading at age 8 years. Sex, socioeconomic status, and nonverbal IQ at age 6 years were associated with reading outcome and were included as covariates in all models. Birth group status significantly moderated associations between reading outcome and mean tract-FA only in the left Arc, right SLF, and left ICP, before and after consideration of pre-literacy skills. Microstructural properties of these cerebral and cerebellar pathways predicted later reading outcome in FT but not in PT children. Children born PT may rely on alternative pathways to achieve fluent reading. These findings have implications for plasticity of neural organization after early white matter injury.
The Cerebellum
Cerebellum-cerebrum connections are essential for many motor and cognitive functions and cerebell... more Cerebellum-cerebrum connections are essential for many motor and cognitive functions and cerebellar disorders are prevalent in childhood. The middle (MCP), inferior (ICP), and superior cerebellar peduncles (SCP) are the major white matter pathways that permit communication between the cerebellum and the cerebrum. Knowledge about the microstructural properties of these cerebellar peduncles across childhood is limited. Here, we report on a diffusion magnetic resonance imaging tractography study to describe age-dependent characteristics of the cerebellar peduncles in a cross-sectional sample of infants, children, and adolescents from newborn to 17 years of age (N = 113). Scans were collected as part of clinical care; participants were restricted to those whose scans showed no abnormal findings and whose history and exam had no risk factors for cerebellar abnormalities. A novel automated tractography protocol was applied. Results showed that mean tract-FA increased, while mean tract-MD decreased from infancy to adolescence in all peduncles. Rapid changes were observed in both diffusion measures in the first 24 months of life, followed by gradual change at older ages. The shape of the tract profiles was similar across ages for all peduncles. These data are the first to characterize the variability of diffusion properties both across and within cerebellar white matter pathways that occur from birth through later adolescence. The data represent a rich normative data set against which white matter alterations seen in children with posterior fossa conditions can be compared. Ultimately, the data will facilitate the identification of sensitive biomarkers of cerebellar abnormalities.
Developmental medicine and child neurology, Jul 3, 2018
To assess associations between white matter properties and pre-reading skills (phonological aware... more To assess associations between white matter properties and pre-reading skills (phonological awareness and receptive and expressive language) in children born preterm and at term at the onset of reading acquisition. Six-year-old children born preterm (n=36; gestational age 22-32wks) and at term (n=43) underwent diffusion magnetic resonance imaging and behavioural assessments. Tracts were selected a priori based on findings from a study of 6-year-old children born at term: the left-hemisphere arcuate fasciculus and superior longitudinal fasciculus, and right-hemisphere uncinate fasciculus. Using linear regression, we assessed associations between fractional anisotropy of tracts and phonological awareness and receptive and expressive language scores. We investigated whether associations were moderated by prematurity. Fractional anisotropy of the left-hemisphere arcuate fasciculus contributed unique variance to phonological awareness across birth groups. The association between fraction...
Scientific Reports
Microsaccades are miniature eye movements that occur involuntarily during fixation. They are typi... more Microsaccades are miniature eye movements that occur involuntarily during fixation. They are typically inhibited following stimulus onset and are released from inhibition about 300 ms post-stimulus. Microsaccade-inhibition is modulated by low level features of visual stimuli, but it is currently unknown whether they are sensitive to higher level, abstract linguistic properties. To address this question, we measured the timing of microsaccades while subjects were presented with written Hebrew words and pronounceable nonwords (pseudowords). We manipulated the underlying structure of pseudowords such that half of them contained real roots while the other half contained invented roots. Importantly, orthographic similarity to real words was equated between the two conditions. Microsaccade onset was significantly slower following real-root compared to invented-root stimuli. Similar results were obtained when considering post-stimulus delay of eye blinks. Moreover, microsaccade-delay was positively and significantly correlated with measures of real-word similarity. These findings demonstrate, for the first time, sensitivity of microsaccades to linguistic structure. Because microsaccades are involuntary and can be measured in the absence of overt response, our results provide initial evidence that they can be used as a novel physiological measure in the study of language processes in healthy and clinical populations.
Journal of Fluency Disorders
Fluent speech production relies on the coordinated processing of multiple brain regions. This hig... more Fluent speech production relies on the coordinated processing of multiple brain regions. This highlights the role of neural pathways that connect distinct brain regions in producing fluent speech. Here, we aim to investigate the role of the white matter pathways in persistent developmental stuttering (PDS), where speech fluency is disrupted. Methods: We use diffusion weighted imaging and tractography to compare the white matter properties between adults who do and do not stutter. We compare the diffusion properties along 18 major cerebral white matter pathways. We complement the analysis with an overview of the methodology and a roadmap of the pathways implicated in PDS according to the existing literature. Results: We report differences in the microstructural properties of the anterior callosum, the right inferior longitudinal fasciculus and the right cingulum in people who stutter compared with fluent controls. Conclusions: Persistent developmental stuttering is consistently associated with differences in bilateral distributed networks. We review evidence showing that PDS involves differences in bilateral dorsal fronto-temporal and fronto-parietal pathways, in callosal pathways, in several motor pathways and in basal ganglia connections. This entails an important role for long range white matter pathways in this disorder. Using a wide-lens analysis, we demonstrate differences in additional, right hemispheric pathways, which go beyond the replicable findings in the literature. This suggests that the affected circuits may extend beyond the known language and motor pathways. Persistent developmental stuttering (PDS) is a speech impairment that disrupts fluent speech production in around 1% of the adult population (Yairi & Ambrose, 1999). Over the years, many attempts have been made to target the neurological underpinnings of PDS using structural and functional imaging methodologies. Here, we report novel findings from a tractography analysis of 18 major white matter pathways segmented in a sample of adults who do and do not stutter. We complement the analysis with an overview of the methodology and existing literature on white matter tracts affected in PDS. We discuss our findings within the context of this literature, and assess the strengths and weaknesses of tractography as a research tool for understanding the white matter properties of people who stutter.
NeuroImage: Clinical
We previously observed a complex pattern of differences in white matter (WM) microstructure betwe... more We previously observed a complex pattern of differences in white matter (WM) microstructure between preterm-born (PT) and full-term-born (FT) children and adolescents age 9-17 years. The aim of this study was to determine if the same differences exist as early as age 6 years. Method: We obtained diffusion MRI (dMRI) scans in children born PT at age 6 years (n = 20; 11 males) and FT (n = 38; 14 males), using two scanning protocols: 30 diffusion directions (b = 1000 s/mm 2) and 96 diffusion directions (b = 2500 s/mm 2). We used deterministic tractography and analyzed fractional anisotropy (FA) along bilateral cerebral WM pathways that demonstrated differences in the older sample. Results: Compared to the FT group, the PT group showed (1) significantly decreased FA in the uncinate fasciculi and forceps major and (2) significantly increased FA in the right anterior thalamic radiation, inferior frontooccipital fasciculi, and inferior longitudinal fasciculi. This pattern of group differences resembles findings in the previous study of older PT and FT participants. Group differences were similar across dMRI acquisition protocols. Interpretation: The underlying neurobiology driving the pattern of PT-FT differences in FA is present as early as age 6 years. Generalization across dMRI acquisition protocols demonstrates the robustness of group differences in FA. Future studies will use quantitative neuroimaging techniques to understand the tissue properties that give rise to this consistent pattern of WM differences after PT birth.
Interhemispheric functional connectivity abnormalities are often reported in autism and it is thu... more Interhemispheric functional connectivity abnormalities are often reported in autism and it is thus not surprising that structural defects of the corpus callosum (CC) are consistently found using both traditional MRI and DTI techniques. Past DTI studies however, have subdivided the CC into 2 or 3 segments without regard for where fibers may project to within the cortex, thus placing limitations on our ability to understand the nature, timing and neurobehavioral impact of early CC abnormalities in autism. Leveraging a unique cohort of 97 toddlers (68 autism; 29 typical) we utilized a novel technique that identified seven CC tracts according to their cortical projections. Results revealed that younger (<2.5 years old), but not older toddlers with autism exhibited abnormally low mean, radial, and axial diffusivity values in the CC tracts connecting the occipital lobes and the temporal lobes. Fractional anisotropy and the cross sectional area of the temporal CC tract were significantl...
Brain Structure and Function, 2016
Reading, an essential life skill in modern society, is typically learned during childhood. Adults... more Reading, an essential life skill in modern society, is typically learned during childhood. Adults who can read show white matter differences compared to adults who never learned to read. Studies have not established whether children who can read show similar white matter differences compared to children who cannot read. We compared 6-year old children who could decode written English words and pseudowords (n=31; Readers) and 6-year old children who could not decode pseudowords and had a standard score < 100 on a task for reading single words (n=11; Pre-Readers). We employed diffusion MRI and tractography to extract fractional anisotropy (FA) along the trajectory of 6 bilateral intra-hemispheric tracts and 2 posterior subdivisions of the corpus callosum. Readers demonstrated significantly increased FA within the left anterior segment of the superior longitudinal fasciculus (aSLF-L) and the right uncinate fasciculus (UF-R) compared to Pre-Readers. FA in the aSLF-L was significantly correlated with phonological awareness; FA in the UF-R was significantly correlated with language. Correlations in the UF-R but not the aSLF-L remained significant after controlling for reading ability, revealing that UF-R group differences were related to both children's language and reading abilities. Taken together, these findings demonstrate new evidence showing that individual differences in white matter structure relate to whether children have begun to read.
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Papers by Michal Ben-shachar