Cerebral laterality of writing in right- and left-handers: A functional transcranial Doppler ultrasound study.

Purpose: Unicoronal synostosis has been associated with impaired reading, language, and social function. Functional MRI (fMRI) can evaluate brain connectivity in targeted brain regions to compare imaging analysis to previously published clinical performance. fMRI was used in this study to compare brain function connectivity in unicoronal synostosis (UCS) and compare outcomes by cerebral dominance (left versus right-sided UCS). Methods: Twelve adolescents with surgically treated UCS, 7 right-sided and 5 left-sided, were individually matched to age, gender and handedness controls. Resting state fMRI was acquired in a 3T Siemens TIM Trio scanner (Erlangen, Germany). Data was collected with intrinsic connectivity distribution and seed-connectivity analysis with BioImage Suite (Yale School of Medicine). Region of interest (ROI) analysis was performed based on Brodmann’s areas (BA) related to emotional, executive, language, motor and visuo-spatial function, left BA5, 6, 7, 18, 19, 37, 39, and 44. BA5, 6, 7 are areas of the frontal and parietal cortex important for visuomotor coordination and complex movement. BA18, 19 are areas of the occipital lobe related to visual information processing. BA 37, 39, and 44 are areas of the fusiform, angular gyri and temporal lobe important for language function. P<0.05 was significant. Results: Compared to controls, all UCS patients demonstrated decreased connectivity in left BA7, bilateral BA39, and right BA41 (p<0.01)), which are areas of the parietal and temporal cortices responsible for vision, language function, and motor coordination. Right UCS patients demonstrated increased connectivity in right BA17, BA18, BA19, BA20, BA36 when compared to controls (p<0.05). In the ROI analysis, right UCS exhibited decreased connectivity between the anterior cingulate cortex and right BA18, 19, and 37 compared to controls (p<0.05). The increased connectivity in BA17-20 (visual processing regions) supports our previous neurocognitive study results of increased visual perception abilities in right UCS patients. The subsequent decreased connectivity between BA18-19 and the anterior cingulate cortex (a section of which is implicated in complex motor coordination) is supported by neurocognitive data that shows decreased visual-motor integration ability in right UCS. This decreased connectivity between the aforementioned areas and the anterior cingulate gyrus despite increased intrinsic connectivity may also imply discordance in connecting emotion and executive function to language and visual information in right UCS patients. Connectivity between the left parahippocampus and right BA36, 37, and 54 was increased (p<0.05). Compared to controls and right UCS, left UCS demonstrated decreased connectivity between left BA6 and left BA17 and 18 (p<0.05). Left UCS patients did not demonstrate significantly different intrinsic or seed-based connectivity to right UCS or controls otherwise. Conclusion: Unilateral coronal synostosis had decreased connectivity and greater potential for neurocognitive dysfunction in regions associated with memory, visual information processing, and motor function. Moreover, left-sided UCS had decreased connectivity in circuits crucial in complex motor movement when compared to right-sided UCS. This study provides data suggestive of long-term sequelae of UCS that varies by sidedness, which may underlie the different phenotypes of neurocognitive impairment found in previous cognitive analyses.

In the majority of people, language production is lateralized to the left cerebral hemisphere and visuospatial skills to the right. However, questions remain as to when, how, and why humans arrive at this division of labor. In this study, we assessed cerebral lateralization for language production and for visuospatial memory using functional transcranial Doppler ultrasound in a group of 60 typically developing children between the ages of six and 16 years. The typical pattern of left-lateralized activation for language production and right-lateralized activation for visuospatial memory was found in the majority of the children (58%). No age-related change in direction or strength of lateralization was found for language production. In contrast, the strength of lateralization (independent of direction) for visuospatial memory function continued to increase with age. In addition, boys showed a trend for stronger right-hemisphere lateralization for visuospatial memory than girls, but there was no gender effect on language laterality. We tested whether having language and visuospatial functions in the same hemisphere was associated with poor cognitive performance and found no evidence for this “functional crowding” hypothesis. We did, however, find that children with left-lateralized language production had higher vocabulary and nonword reading age-adjusted standard scores than other children, regardless of the laterality of visuospatial memory. Thus, a link between language function and left-hemisphere lateralization exists, and cannot be explained in terms of maturational change.

Research utilising handedness as a proxy for atypical language lateralisation has invoked the latter to explain increased mental health difficulties in left-/mixed-handed children. The current study investigated unique associations between handedness and language lateralisation, handedness and mental health, and language lateralisation and mental health, in children, to elucidate the role of cerebral lateralisation in paediatric mental health. Participants were N = 64 (34 females [52%]; MAge = 8.56 years; SDAge = 1.33; aged 6-12 years) typically developing children. Hand preference was assessed via a reaching task, language lateralisation was assessed using functional transcranial Doppler ultrasonography (fTCD) during an expressive language task, and mental health was assessed with the Strengths and Difficulties Questionnaire. As hypothesised, leftward hand preference predicted increased general mental health issues in children, with a strong relationship noted between leftward hand preference and the emotional symptoms subscale. Contrary to expectation, no relationship was found between direction of language lateralisation and general mental health issues, although exploratory analyses of subscales showed rightward lateralisation to predict conduct problems. Hand preference and direction of language lateralisation were also not significantly associated. The relatively weak relationship between manual and language laterality coupled with discrepancy regarding the predictive scope of each phenotype (i.e., hand preference predicts overall mental health, whereas language laterality predicts only conduct problems) suggests independent developmental pathways for these phenotypes. The role of manual laterality in paediatric mental health warrants further investigation utilising a neuroimaging method with higher spatial resolution.

Many eye tracking studies of visual search have focused on the role of the number of fixations and the nature of scan paths. Less attention has been paid to fixation durations and to how those durations are affected by stimulus features. Previous studies have shown that fixation durations can be as important as the number of fixations in explaining search times with complex stimuli (e.g., in search for specific faces). In the present study, simple stimuli were used in a search experiment where participants searched for a closed ring among rings with a gap. We manipulated distractor heterogeneity (DH), target-distractor similarity (TDS), and stimulus density (SDY, set size within a constant search window), and estimated the contributions of these factors to gaze behaviour and trial search time. The results show that fixation durations contribute less to variation in overall search time with simple search stimuli as compared to previous studies with more complex stimuli. However, fixation durations still increased with DH, TDS, and SDY. These effects were mainly additive, and we did not find an interaction between DH and closer element spacing at high levels of SDY that might have been expected since both DH and SDY influence distractor grouping.

Chapter 6 - Lateralization of the human brain

Aiming to investigate whether handedness-related language lateralization is related to the intrinsic resting-state functional connectivity (RSFC) pattern within the language network, the present study integrated the information of functional activations during a semantic task of Chinese characters and FC in resting-state based on functional magnetic resonance imaging (fMRI) data of healthy left handers (LH) and right handers (RH). RSFC was calculated on a voxel-based level between the seed regions chosen from functional activations during the task and the rest of the brain. The results demonstrated that LH had significantly stronger RSFC than RH between the cerebellum and supratentorial areas of the frontal, parietal and temporal lobe, and between the occipital lobe and frontal/parietal lobe. Correlation analysis showed that RSFC values between right MFG and left cerebellum_crus2, between SMA and right cerebellum_crus2, and between the right cerebellum_crus1 and left MFG were negatively correlated with cerebral laterality index in LH and RH groups. Our results highlight key nodes of Chinese language brain network processing in the cerebellum, and suggest that atypical language dominance relates to stronger crossed reciprocal RSFC in the frontal-cerebellar system. The findings provide new insights into the intrinsic FC substrates underlying the atypical language lateralization of LH.

Determining language dominance with fMRI is challenging in patients with brain tumor, particularly in cases of suspected atypical language representation. Supratentorial activation patterns must be interpreted with great care when the tumor is in or near the presumed language areas, where tumor tissue or mass effect can lead to false-negative fMRI results. In this study, we assessed cerebrocerebellar language fMRI lateralization in healthy participants and in patients with brain tumors with a focus on atypical language representation. Twenty healthy participants and 38 patients with a brain tumor underwent fMRI with a verb-generation task. Cerebral and cerebellar language lateralizations were separately classified as left-sided, right-sided, or symmetric. Electrocortical stimulation was performed in 19 patients. With the McNemar test, we evaluated the dependency between language lateralization in the cerebrum and cerebellum, and with Pearson correlation analysis, the relationship between the cerebral and cerebellar lateralization indices. There was a significant dependency between cerebral and cerebellar language activation, with moderate negative correlation (Pearson r = -0.69). Crossed cerebrocerebellar language activation was present in both healthy participants and patients, irrespective of handedness or typical or atypical language representation. There were no discordant findings between fMRI and electrocortical stimulation. Language lateralization in the cerebellum can be considered an additional diagnostic feature to determine language dominance in patients with brain tumor. This is particularly useful in cases of uncertainty, such as the interference of a brain tumor with cerebral language activation on fMRI and atypical language representation.

IntroductionPerception under noisy conditions requires not only feature identification but also a process whereby target features are selected and noise is filtered out (e.g., when identifying an animal hiding in the savannah). Interestingly, previous perceptual learning studies demonstrated the utility of training feature representation (without noise) for improving discrimination under noisy conditions. Furthermore, learning to filter out noise also appears to transfer to other perceptual task under similar noisy conditions. However, such learning transfer effects were thus far demonstrated predominantly in simple stimuli. Here we sought to explore whether similar learning transfer can be observed with complex real-world stimuli.MethodsWe assessed the feature-to-noise transfer effect by using complex stimuli of human faces. We first examined participants' performance on a face-noise task following either training in the same task, or in a different face-feature task. Second, we assessed the transfer effect across different noise tasks defined by stimulus complexity, simple stimuli (Gabor) and complex stimuli (faces).ResultsWe found a clear learning transfer effect in the face-noise task following learning of face features. In contrast, we did not find transfer effect across the different noise tasks (from Gabor-noise to face-noise).ConclusionThese results extend previous findings regarding transfer of feature learning to noisy conditions using real-life stimuli.

Individuals born prematurely are at risk for developmental delay, and converging data suggest alterations in neural networks in the developing preterm brain. Nevertheless, those critical period processes such as cerebral lateralization that underlie these findings remain largely unexplored. To test the hypothesis that preterm birth alters the fundamental program of corticogenesis in the developing brain, we interrogated cerebral lateralization at rest in very prematurely born participants and term controls at young adulthood. Employing a novel, voxel-based measure of functional connectivity, these data demonstrate for the first time that cerebral lateralization of functional connectivity in right hemisphere language homologs is altered for very preterm participants. Very preterm participants with no evidence for severe brain injury exhibited a significant decrease in right hemisphere lateralization in the right parietal and temporal lobes in this data driven analysis. Further, for the very preterm participants, but not the term participants, these fundamental alterations in the cerebral lateralization for language significantly correlate with language scores. These findings provide evidence that cerebral asymmetry is both plastic and experiential, and suggest the need for further study of underlying environmental factors responsible for these changes.

Cerebral lateralization of written language, much like oral language, is predominantly left lateralized. However, handwriting has been the primary focus in lateralization studies. The cerebral lateralization of typing-a widely used method of writing-remains unexamined. This preregistered study aimed to explore the cerebral lateralization of typing versus handwriting and to investigate possible handedness-related differences. We hypothesized that (i) cerebral lateralization would not differ between the two writing methods after movement correction and (ii) both handwriting and typing would show weaker lateralization in left-handers compared to right-handers. To investigate this, we used functional transcranial Doppler (fTCD) ultrasound, a reliable method for assessing cerebral lateralization during language tasks that remains unaffected by movement artifacts, such as those generated by handwriting and typing. A total of 24 left-handers and 30 right-handers participated, performing written word generation through both handwriting and typing on a computer keyboard while undergoing fTCD assessment. We applied a Bayesian framework for our analysis, as it enables us to demonstrate the absence of a difference (i.e., no difference between two variables), which is not possible with the use of p values (estimated under the frequentist framework). Our results provided evidence supporting the absence of a difference in cerebral lateralization between handwriting and typing after movement correction. However, we found no conclusive evidence to either support or refute a difference in lateralization between left-handers and right-handers, suggesting that more research is needed to clarify the role of handedness in cerebral lateralization for different writing methods.

Apraxia, Handedness and Language Laterality

To the Editor: I read with interest the article by Hund-Georgiadis et al1 on crossed nonaphasia in a dextral with left hemispheric lesions published in the November 2001 issue of Stroke . They concluded from their data that different modalities such as language perception and production, attention, and motor performance are processed exclusively by one hemisphere when atypical cerebral dominance is present. They also suggested that the underlying functional organization of language remains rare and unclear in these cases. Our studies in normal subjects using functional transcranial Doppler (fTCD) suggest that this may not be rare after all. Left hemispheric lateralization for language was found in 61.5% of neurologically intact dextrals.2 Human pathology data obtained by Geschwind and Levitsky3 found that the planum temporale of the temporoparietal junction is larger in the left hemisphere in ≈60% of the population.3 Furthermore, there was a high incidence of right-hemisphere lateralization for language in as much as 38.5% of neurologically intact dextrals.2 Dyslexics had a pattern that was opposite the normal pattern.2 Recently, the use of functional MRI and fTCD offers new approaches with more precise determinations of cerebral lateralization for language. To support the …

Motor and language deficits before and after surgical resection of mesial frontal tumour

Resection of lesions involving the supplementary motor area (SMA) may result in immediate postoperative motor and speech deficits that are reversible in most cases. In the present study the authors aimed to determine the critical involvement of SMA in the lesioned and healthy hemispheres in this functional recovery. They hypothesized that compensatory mechanisms take place following surgery in the SMA, and that these mechanisms can involve either the lesioned or the non-lesioned hemisphere. In addition, they hypothesized that a correlation will be present between the functional MR imaging (fMR) imaging-related activation in the SMA and the occurrence of a functional deficit during intraoperative cortical stimulation. Twenty-six patients scheduled for resection of space-occupying lesions involving, or in the vicinity of, the SMA were recruited. Patients underwent an fMR imaging examination that included finger-tapping and verb-generation tests to assess for motor and language functions. Intraoperatively direct cortical stimulation (DCS) of the SMA region was performed while patients were monitored for language and motor functions using tests similar to those used for the fMR imaging. Task dysfunction during DCS assessed the critical involvement of the SMA in the tested functions. Neurological evaluations were performed prior to surgery and at 3 time points within a month following surgery. A region of interest-based approach was used to evaluate fMR imaging blood oxygen level-dependent activation level and asymmetry in the SMA. These measurements were later compared with the intraoperative DCS and neurological findings. Functional MR imaging showed greater activation and dominance of the SMA in the lesioned hemisphere in patients who exhibited no motor or language dysfunction during DCS. In addition, patients with the highest activation of the SMA in the lesioned hemisphere for language and motor tests showed stronger coupling of this region with ipsilateral motor and language networks. In contrast, activation in the nonlesioned hemisphere did not correspond with DCS results. The authors' findings demonstrate the necessity of activation in the vicinity of the lesioned SMA for functional compensation in motor and language tasks. It is possible that more effective functional coupling of the SMA with motor and language areas in the same hemisphere prevents dysfunctions following surgical intervention. Importantly, fMR imaging activation in the unaffected SMA was not sufficient for development of functional compensation and, if anything, indicated decompensation.

Evidence for common mechanisms in the human brain for motor and language functions is reviewed, particularly evidence derived from electrical-stimulation mapping during cortical and thalamic operations in awake patients. Several systems in the dominant hemisphere are identified where language and motor function share common mechanisms, including a lateral thalamic attentional system and a lateral perisylvian cortical system common to sequential movement and speech sound identification, where precise timing may be a common mechanism.