Assessment of hemispheric language lateralization: a comparison between fMRI and fTCD

Generalized models for estimating cerebral lateralisation of young children using functional transcranial Doppler ultrasound

Thompson et al., 2023 (Generalized models for quantifying laterality using functional transcranial Doppler ultrasound. Human Brain Mapping, 44(1), 35-48) introduced generalised model-based analysis methods for determining cerebral lateralisation from functional transcranial Doppler ultrasound (fTCD) data which substantially decreased the uncertainty of individual lateralisation estimates across several large adult samples. We aimed to assess the suitability of these methods for increasing precision in lateralisation estimates for child fTCD data. We applied these methods to adult fTCD data to establish the validity of two child-friendly language and visuospatial tasks. We also applied the methods to fTCD data from 4- to 7-year-old children. For both samples, the laterality estimates from the complex generalised additive model (GAM) approach correlated strongly with the traditional methods while also decreasing individual standard errors compared to the popular period-of-interest averaging method. We recommend future research using fTCD with young children consider using GAMs to reduce the noise in their LI estimates.

Exploring cerebral laterality of writing and the relationship to handedness: a functional transcranial Doppler ultrasound investigation

Cerebral lateralization of oral language has been investigated in a plethora of studies and it is well established that the left hemisphere is dominant for production tasks in the majority of individuals. However, few studies have focused on written language and even fewer have sampled left-handers. Writing comprises language and motor components, both of which contribute to cerebral activation, yet previous research has not disentangled. The aim of this study was to disentangle the language and motor components of writing lateralization. This was achieved through the comparison of cerebral activation during (i) written word generation and (ii) letter copying, as assessed by functional Transcranial Doppler (fTCD) ultrasound. We further assessed cerebral laterality of oral language. The sample was balanced for handedness. We preregistered the hypotheses that (i) cerebral lateralization of the linguistic component of writing would be weaker in left-handers compared to right-handers and (ii) oral language and the linguistic component of written language would not be correlated in terms of cerebral lateralization. No compelling evidence for either of our hypotheses was found. Findings highlight the complexity of the processes subserving written and oral language as well as the methodological challenges to isolate the linguistic component of writing.

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

The cerebral lateralization of written language has received very limited research attention in comparison to the wealth of studies on the cerebral lateralization of oral language. The purpose of the present study was to further our understanding of written language lateralization, by elucidating the relative contribution of language and motor functions. We compared written word generation with a task that has equivalent visuomotor demands but does not include language: the repeated drawing of symbols. We assessed cerebral laterality using functional transcranial Doppler ultrasound (fTCD), a non-invasive, perfusion-sensitive neuroimaging technique in 23 left- and 31 right-handed participants. Findings suggest that the linguistic aspect of written word generation recruited more left-hemispheric areas during writing, in right-handers compared to left-handers. This difference could be explained by greater variability in cerebral laterality patterns within left-handers or the possibility that the areas subserving language in left-handers are broader than in right-handers. Another explanation is that the attentional demands of the more novel symbol copying task (compared to writing) contributed more right-hemispheric activation in right-handers, but this could not be captured in left-handers due to ceiling effects. Future work could investigate such attentional demands using both simple and complex stimuli in the copying condition.

The scalability of common paradigms for assessment of cognitive function: A functional transcranial Doppler study

Cognitive paradigms induce changes in cerebral blood flow (CBF) associated with increased metabolic demand, namely neurovascular coupling (NVC). We tested the hypothesis that the effect of complexity and duration of cognitive paradigms will either enhance or inhibit the NVC response. Bilateral CBF velocity (CBFV) in the middle cerebral arteries (MCAs) via transcranial Doppler ultrasound (TCD), blood pressure (BP), electrocardiogram (ECG) and end-tidal CO₂ (EtCO₂) of 16 healthy participants (aged 21–71 years) were simultaneously recorded at rest and during randomized paradigms of different complexities (naming words beginning with P-,R-,V- words and serial subtractions of 100–2,100–7,1000–17), and durations (5s, 30s and 60s). CBFV responses were population mean normalized from a 30-s baseline period prior to task initiation. A significant increase in bilateral CBFV response was observed at the start of all paradigms and provided a similar pattern in most responses, irrespective of complexity or duration. Although significant inter-hemispherical differences were found during performance of R-word and all serial subtraction paradigms, no lateralisation was observed in more complex naming word tasks. Also, the effect of duration was manifested at late stages of 100–7, but not for other paradigms. CBFV responses could not distinguish different levels of complexity or duration with a single presentation of the cognitive paradigm. Further studies of the ordinal scalability of the NVC response are needed with more advanced modelling techniques, or different types of neural stimulation.

Evaluation of a Simple Clinical Language Paradigm With Respect to Sensory Independency, Functional Asymmetry, and Effective Connectivity

The present study replicates a known visual language paradigm, and extends it to a paradigm that is independent from the sensory modality of the stimuli and, hence, could be administered either visually or aurally, such that both patients with limited sight or hearing could be examined. The stimuli were simple sentences, but required the subject not only to understand the content of the sentence but also to formulate a response that had a semantic relation to the content of the presented sentence. Thereby, this paradigm does not only test perception of the stimuli, but also to some extend sentence and semantic processing, and covert speech production within one task. When the sensory base-line condition was subtracted, both the auditory and visual version of the paradigm demonstrated a broadly overlapping and asymmetric network, comprising distinct areas of the left posterior temporal lobe, left inferior frontal areas, left precentral gyrus, and supplementary motor area. The consistency of activations and their asymmetry was evaluated with a conjunction analysis, probability maps, and intraclass correlation coefficients (ICC). This underlying network was further analyzed with dynamic causal modeling (DCM) to explore whether not only the same brain areas were involved, but also the network structure and information flow were the same between the sensory modalities. In conclusion, the paradigm reliably activated the most central parts of the speech and language network with a great consistency across subjects, and independently of whether the stimuli were administered aurally or visually. However, there was individual variability in the degree of functional asymmetry between the two sensory conditions.

Measurement of language laterality using functional transcranial Doppler ultrasound: a comparison of different tasks

Background: Relative blood flow in the two middle cerebral arteries can be measured using functional transcranial Doppler sonography (fTCD) to give an index of lateralisation as participants perform a specific task. Language laterality has mostly been studied with fTCD using a word generation task, but it is not clear whether this is optimal. Methods: Using fTCD, we evaluated a sentence generation task that has shown good reliability and strong left lateralisation in fMRI. We interleaved trials of word generation, sentence generation and list generation and assessed agreement of these tasks in 31 participants (29 right-handers). Results: Although word generation and sentence generation both gave robust left-lateralisation, lateralisation was significantly stronger for sentence generation. Bland-Altman analysis showed that these two methods were not equivalent. The comparison list generation task was not systematically lateralised, but nevertheless laterality indices (LIs) from this task were significantly correlated with the other two tasks. Subtracting list generation LI from sentence generation LI did not affect the strength of the laterality index. Conclusions: This was a pre-registered methodological study designed to explore novel approaches to optimising measurement of language lateralisation using fTCD. It confirmed that sentence generation gives robust left lateralisation in most people, but is not equivalent to the classic word generation task. Although list generation does not show left-lateralisation at the group level, the LI on this task was correlated with left-lateralised tasks. This suggests that word and sentence generation involve adding a constant directional bias to an underlying continuum of laterality that is reliable in individuals but not biased in either direction. In future research we suggest that consistency of laterality across tasks might have more functional significance than strength or direction of laterality on any one task.

Measurement of language laterality using functional transcranial Doppler ultrasound: a comparison of different tasks

Background: Relative blood flow in the two middle cerebral arteries can be measured using functional transcranial Doppler sonography (fTCD) to give an index of lateralisation as participants perform a specific task. Language laterality has mostly been studied with fTCD using a word generation task, but it is not clear whether this is optimal. Methods: Using fTCD, we evaluated a sentence generation task that has shown good reliability and strong left lateralisation in fMRI. We interleaved trials of word generation, sentence generation and list generation and assessed agreement of these tasks in 31 participants (29 right-handers). Results: Although word generation and sentence generation both gave robust left-lateralisation, lateralisation was significantly stronger for sentence generation. Bland-Altman analysis showed that these two methods were not equivalent. The comparison list generation task was not systematically lateralised, but nevertheless laterality indices (LIs) from this task were significantly correlated with the other two tasks. Subtracting list generation LI from sentence generation LI did not affect the strength of the laterality index. Conclusions: This was a pre-registered methodological study designed to explore novel approaches to optimising measurement of language lateralisation using fTCD. It confirmed that sentence generation gives robust left lateralisation in most people, but is not equivalent to the classic word generation task. Although list generation does not show left-lateralisation at the group level, the LI on this task was correlated with left-lateralised tasks. This suggests that word and sentence generation involve adding a constant directional bias to an underlying continuum of laterality that is reliable in individuals but not biased in either direction. In future research we suggest that consistency of laterality across tasks might have more functional significance than strength or direction of laterality on any one task.

Hemispheric language lateralization in presurgical patients with temporal lobe epilepsy: Improving the retest reliability of functional transcranial Doppler sonography

Since its introduction, functional transcranial Doppler sonography (fTCD) has been extensively applied in research and clinical settings and has now become part of the routine presurgical work-up of patients with epilepsy. Because of its importance in planning neurosurgical interventions and predicting possible cognitive risks, the reproducibility of fTCD in determining hemispheric language lateralization (HLL) has to be ensured. In the present study, fTCD was performed twice in 33 initially lateralized patients with temporal lobe epilepsy (TLE) as part of their presurgical work-up, using a standard word generation paradigm. Initially, the standard analysis, including only the statistical examination of fTCD data, was applied, and a rather poor retest reliability of r = 0.41 was obtained (p = 0.017). Because of doubts concerning appropriate task performance in some patients, subsequently, a two-step data analysis was introduced, including an additional qualitative evaluation of fTCD data regarding (1) instruction-compliant task performance, (2) sufficient quality of the baseline phase, and (3) adequate increase in cerebral blood flow velocity (CBFV) during the activation phase. Attributable to a more valid interpretation of fTCD data after the application of the qualitative step, the reproducibility of HLL significantly improved (p = 0.007) to a high retest reliability of r = 0.84 (p < 0.000). In clinical settings, psychological and situational factors seem to strongly influence the reproducibility of fTCD determining HLL. Accordingly, we highly recommend the complementation of the standard statistical examination of fTCD data by an additional qualitative evaluation (two-step data analysis), as this extra security is particularly desirable because of its direct implications for the further evaluation of neurosurgical interventions. This article is part of the Special Issue "Individualized Epilepsy Management: Medicines, Surgery and Beyond".

Measurement of language laterality using functional transcranial Doppler ultrasound: a comparison of different tasks

Background: Relative blood flow in the two middle cerebral arteries can be measured using functional transcranial Doppler sonography (fTCD) to give an index of lateralisation as participants perform a specific task. Language laterality has mostly been studied with fTCD using a word generation task, but it is not clear whether this is optimal. Methods: Using fTCD, we evaluated a sentence generation task that has shown good reliability and strong left lateralisation in fMRI. We interleaved trials of word generation, sentence generation and list generation and assessed agreement of these tasks in 31 participants (29 right-handers). Results: Although word generation and sentence generation both gave robust left-lateralisation, Bland-Altman analysis showed that these two methods were not equivalent. The comparison list generation task was not systematically lateralised, but nevertheless laterality indices (LIs) from this task were significantly correlated with the other two tasks. Subtracting list generation LI from sentence generation LI did not affect the strength of the laterality index. Conclusions: This was a pre-registered methodological study designed to explore novel approaches to optimising measurement of language lateralisation using fTCD. It confirmed that sentence generation gives robust left lateralisation in most people, but is not equivalent to the classic word generation task. Although list generation does not show left-lateralisation at the group level, the LI on this task was correlated with left-lateralised tasks. This suggests that word and sentence generation involve adding a constant directional bias to an underlying continuum of laterality that is reliable in individuals but not biased in either direction. In future research we suggest that consistency of laterality across tasks might have more functional significance than strength or direction of laterality on any one task.

Cerebral blood flow modulations during preparatory attention and proactive inhibition

This study investigated cerebral blood flow modulations during task preparation in a precued saccade paradigm. Bilateral blood flow velocities in the middle cerebral arteries were recorded in 48 subjects using functional transcranial Doppler sonography. Video-based eye-tracking was applied for ocular recording. Antisaccade and prosaccade trials were presented in both block-wise and interleaved order. A right dominant flow response arose during task preparation. While the response was stronger during antisaccade than prosaccade trials, the degree of lateralisation did not differ between the two trial types. Direction error rates were higher and latencies were longer for antisaccades than prosaccades. There were no differences between block-wise and interleaved trials in blood flow or performance. The stronger blood flow increases during antisaccade than prosaccade preparation reflects the complexity of the upcoming task demands as well as proactive inhibition. The right hemispheric lateralisation may be attributed to preparatory attention independent of demands on inhibitory control.

The assessment of neurovascular coupling with the Addenbrooke’s Cognitive Examination: a functional transcranial Doppler ultrasonographic study

Cerebrovascular dysfunction occurs early in dementia and can be identified by transcranial Doppler ultrasonography (TCD). Few studies have examined cerebral blood flow velocity (CBFv) responses to a detailed cognitive battery. This study aimed to characterize all CBFv responses, and the effect of hemispheric dominance, to the Addenbrooke’s Cognitive Examination (ACE-III) in healthy volunteers. Forty volunteers underwent continuous bilateral TCD, beat-to-beat blood pressure (MAP; Finapres), heart rate (HR; electrocardiogram), and end-tidal CO2 (ETCO2; capnography) monitoring. After a 5-min baseline period, all tasks from the ACE-III were performed in 3 sections (A: attention, fluency, memory; B: language; C: visuospatial, memory). Data are population mean normalized percentage (PM%) change from a 20-s baseline period before task initiation. Forty bilateral data sets were obtained (27 women, 37 right-hand dominant). All paradigms produced a sharp increase in CBFv in both dominant (PM% range: 3.29 to 9.70%) and nondominant (PM% range: 4.34 to 11.63%) hemispheres at task initiation, with associated increases in MAP (PM% range: 3.06 to 16.04%). ETCO2 did not differ significantly at task initiation (PM% range: −1.1 to 2.4%, P > 0.05). HR differed significantly across A and C tasks at initiation (PM% range: −1.1 to 2.4%, P < 0.05), but not B tasks. In conclusion, all tasks resulted in increases in CBFv, differing significantly between paradigms. These results require further investigation in a cognitively impaired population.

NEW & NOTEWORTHY This study is the first to provide a normative data set of cerebral blood flow velocity (CBFv) responses to a complete cognitive assessment (Addenbrooke’s Cognitive Examination, ACE-III) in a large sample ( n = 40) of healthy volunteers. All tasks produced peak and sustained increases in CBFv to different extents. The ACE-III is a feasible tool to assess neurovascular coupling with transcranial Doppler ultrasonography. These data can be used to inform the most appropriate cognitive task to elicit CBFv responses for future studies.

Prenatal and pubertal testosterone affect brain lateralization

After decades of research, the influence of prenatal testosterone on brain lateralization is still elusive, whereas the influence of pubertal testosterone on functional brain lateralization has not been investigated, although there is increasing evidence that testosterone affects the brain in puberty. We performed a longitudinal study, investigating the relationship between prenatal testosterone concentrations in amniotic fluid, pubertal testosterone concentrations in saliva, and brain lateralization (measured with functional Transcranial Doppler ultrasonography (fTCD)) of the Mental Rotation, Chimeric Faces and Word Generation tasks. Thirty boys and 30 girls participated in this study at the age of 15 years. For boys, we found a significant interaction effect between prenatal and pubertal testosterone on lateralization of Mental Rotation and Chimeric Faces. In the boys with low prenatal testosterone levels, pubertal testosterone was positively related to the strength of lateralization in the right hemisphere, while in the boys with high prenatal testosterone levels, pubertal testosterone was negatively related to the strength of lateralization. For Word Generation, pubertal testosterone was negatively related to the strength of lateralization in the left hemisphere in boys. For girls, we did not find any significant effects, possibly because their pubertal testosterone levels were in many cases below quantification limit. To conclude, prenatal and pubertal testosterone affect lateralization in a task-specific way. Our findings cannot be explained by simple models of prenatal testosterone affecting brain lateralization in a similar way for all tasks. We discuss alternative models involving age dependent effects of testosterone, with a role for androgen receptor distribution and efficiency.

Resounding failure to replicate links between developmental language disorder and cerebral lateralisation

Background

It has been suggested that failure to establish cerebral lateralisation may be related to developmental language disorder (DLD). There has been weak support for any link with handedness, but more consistent reports of associations with functional brain lateralisation for language. The consistency of lateralisation across different functions may also be important. We aimed to replicate previous findings of an association between DLD and reduced laterality on a quantitative measure of hand preference (reaching across the midline) and on language laterality assessed using functional transcranial Doppler ultrasound (fTCD).

Methods

From a sample of twin children aged from 6;0 to 11;11 years, we identified 107 cases of DLD and 156 typically-developing comparison cases for whom we had useable data from fTCD yielding a laterality index (LI) for language function during an animation description task. Handedness data were also available for these children.

Results

Indices of handedness and language laterality for this twin sample were similar to those previously reported for single-born children. There were no differences between the DLD and TD groups on measures of handedness or language lateralisation, or on a categorical measure of consistency of left hemisphere dominance. Contrary to prediction, there was a greater incidence of right lateralisation for language in the TD group (19.90%) than the DLD group (9.30%), confirming that atypical laterality is not inconsistent with typical language development. We also failed to replicate associations between language laterality and language test scores.

Discussion and Conclusions

Given the large sample studied here and the range of measures, we suggest that previous reports of atypical manual or language lateralisation in DLD may have been false positives.

Comparison of fMRI paradigms assessing visuospatial processing: Robustness and reproducibility

The development of brain imaging techniques, in particular functional magnetic resonance imaging (fMRI), made it possible to non-invasively study the hemispheric lateralization of cognitive brain functions in large cohorts. Comprehensive models of hemispheric lateralization are, however, still missing and should not only account for the hemispheric specialization of individual brain functions, but also for the interactions among different lateralized cognitive processes (e.g., language and visuospatial processing). This calls for robust and reliable paradigms to study hemispheric lateralization for various cognitive functions. While numerous reliable imaging paradigms have been developed for language, which represents the most prominent left-lateralized brain function, the reliability of imaging paradigms investigating typically right-lateralized brain functions, such as visuospatial processing, has received comparatively less attention. In the present study, we aimed to establish an fMRI paradigm that robustly and reliably identifies right-hemispheric activation evoked by visuospatial processing in individual subjects. In a first study, we therefore compared three frequently used paradigms for assessing visuospatial processing and evaluated their utility to robustly detect right-lateralized brain activity on a single-subject level. In a second study, we then assessed the test-retest reliability of the so-called Landmark task–the paradigm that yielded the most robust results in study 1. At the single-voxel level, we found poor reliability of the brain activation underlying visuospatial attention. This suggests that poor signal-to-noise ratios can become a limiting factor for test-retest reliability. This represents a common detriment of fMRI paradigms investigating visuospatial attention in general and therefore highlights the need for careful considerations of both the possibilities and limitations of the respective fMRI paradigm–in particular, when being interested in effects at the single-voxel level. Notably, however, when focusing on the reliability of measures of hemispheric lateralization (which was the main goal of study 2), we show that hemispheric dominance (quantified by the lateralization index, LI, with |LI| >0.4) of the evoked activation could be robustly determined in more than 62% and, if considering only two categories (i.e., left, right), in more than 93% of our subjects. Furthermore, the reliability of the lateralization strength (LI) was “fair” to “good”. In conclusion, our results suggest that the degree of right-hemispheric dominance during visuospatial processing can be reliably determined using the Landmark task, both at the group and single-subject level, while at the same time stressing the need for future refinements of experimental paradigms and more sophisticated fMRI data acquisition techniques.

What Box: A task for assessing language lateralization in young children

The assessment of active language lateralization in infants and toddlers is challenging. It requires an imaging tool that is unintimidating, quick to setup, and robust to movement, in addition to an engaging and cognitively simple language processing task. Functional Transcranial Doppler Ultrasound (fTCD) offers a suitable technique and here we report on a suitable method to elicit active language production in young children. The 34-second "What Box" trial presents an animated face "searching" for an object. The face "finds" a box that opens to reveal a to-be-labelled object. In a sample of 95 children (1 to 5 years of age), 81% completed the task-32% with ≥10 trials. The task was validated (ρ = 0.4) against the gold standard Word Generation task in a group of older adults (n = 65, 60-85 years of age), though was less likely to categorize lateralization as left or right, indicative of greater measurement variability. Existing methods for active language production have been used with 2-year-old children while passive listening has been conducted with sleeping 6-month-olds. This is the first active method to be successfully employed with infants through to pre-schoolers, forming a useful tool for populations in which complex instructions are problematic.

Cerebral laterality for language is related to adult salivary testosterone levels but not digit ratio (2D:4D) in men: A functional transcranial Doppler ultrasound study

The adequacy of three competing theories of hormonal effects on cerebral laterality are compared using functional transcranial Doppler sonography (fTCD). Thirty-three adult males participated in the study (21 left-handers). Cerebral lateralization was measured by fTCD using an extensively validated word generation task. Adult salivary testosterone (T) and cortisol (C) concentrations were measured by luminescence immunoassay and prenatal T exposure was indirectly estimated by the somatic marker of 2nd to 4th digit length ratio (2D:4D). A significant quadratic relationship between degree of cerebral laterality for language and adult T concentrations was observed, with enhanced T levels for strong left hemisphere dominance and strong right hemisphere dominance. No systematic effects on laterality were found for cortisol or 2D:4D. Findings suggest that higher levels of T are associated with a relatively attenuated degree of interhemispheric sharing of linguistic information, providing support for the callosal and the sexual differentiation hypotheses rather than the Geschwind, Behan and Galaburda (GBG) hypothesis.

Language lateralization of hearing native signers: A functional transcranial Doppler sonography (fTCD) study of speech and sign production

Neuroimaging studies suggest greater involvement of the left parietal lobe in sign language compared to speech production. This stronger activation might be linked to the specific demands of sign encoding and proprioceptive monitoring. In Experiment 1 we investigate hemispheric lateralization during sign and speech generation in hearing native users of English and British Sign Language (BSL). Participants exhibited stronger lateralization during BSL than English production. In Experiment 2 we investigated whether this increased lateralization index could be due exclusively to the higher motoric demands of sign production. Sign naïve participants performed a phonological fluency task in English and a non-sign repetition task. Participants were left lateralized in the phonological fluency task but there was no consistent pattern of lateralization for the non-sign repetition in these hearing non-signers. The current data demonstrate stronger left hemisphere lateralization for producing signs than speech, which was not primarily driven by motoric articulatory demands.

The Posterior Cerebral Artery and its Main Cortical Branches Identified with Noninvasive Transcranial Color-Coded Duplex Sonography

PURPOSE

To differentiate PCA segments and cortical branches by means of transcranial color-coded duplex sonography (TCCD) and to measure flow parameters at rest and during visual stimulation.

MATERIALS AND METHODS

60 healthy subjects with a good acoustic temporal bone window were examined. The main stem of the PCA (P1, P2 and P3) and 4 main cortical branches - the anterior temporal artery (ATA), the occipital temporal artery (OTA), the parietooccipital artery (POA) and the calcarine artery (CA) - were assessed using an axial transtemporal approach. Systolic and diastolic blood flow velocities (BFVs) were recorded at rest and during visual stimulation.

RESULTS

Identification of the P1 segment of the PCA was successful in 97.5% (117/120) of cases. The P2 and P3 segments were visualized in all cases. The 4 main cortical branches could be identified to varying degrees: ATA in 88%, OTA in 96%, POA in 69% and CA in 62%. There was an evoked flow response in the P2 main stem and in all cortical branches. The most pronounced increase in diastolic/systolic BFV after visual stimulation test was seen in the CA (42%/35%), followed by P2 (30%/24%), the POA (27%/27%), the OTA (16%/13%) and the ATA (9%/8%).

CONCLUSION

Insonation through the temporal bone window with TCCD confidently allows the assessment of the P1 to P3 segments of the PCA as well as the 2 proximal branches, the ATA and the OTA. An ultrasound-based classification of PCA anatomy and its cortical branches may be used as a noninvasive method for the evaluation of posterior circulation pathology.

Stimulus rate increases lateralisation in linguistic and non-linguistic tasks measured by functional transcranial Doppler sonography

Studies to date that have used fTCD to examine language lateralisation have predominantly used word or sentence generation tasks. Here we sought to further assess the sensitivity of fTCD to language lateralisation by using a metalinguistic task which does not involve novel speech generation: rhyme judgement in response to written words. Line array judgement was included as a non-linguistic visuospatial task to examine the relative strength of left and right hemisphere lateralisation within the same individuals when output requirements of the tasks are matched. These externally paced tasks allowed us to manipulate the number of stimuli presented to participants and thus assess the influence of pace on the strength of lateralisation. In Experiment 1, 28 right-handed adults participated in rhyme and line array judgement tasks and showed reliable left and right lateralisation at the group level for each task, respectively. In Experiment 2 we increased the pace of the tasks, presenting more stimuli per trial. We measured laterality indices (LIs) from 18 participants who performed both linguistic and non-linguistic judgement tasks during the original 'slow' presentation rate (5 judgements per trial) and a fast presentation rate (10 judgements per trial). The increase in pace led to increased strength of lateralisation in both the rhyme and line conditions. Our results demonstrate for the first time that fTCD is sensitive to the left lateralised processes involved in metalinguistic judgements. Our data also suggest that changes in the strength of language lateralisation, as measured by fTCD, are not driven by articulatory demands alone. The current results suggest that at least one aspect of task difficulty, the pace of stimulus presentation, influences the strength of lateralisation during both linguistic and non-linguistic tasks.

On the relationship between degree of hand-preference and degree of language lateralization

Language lateralization and hand-preference show inter-individual variation in the degree of lateralization to the left- or right, but their relation is not fully understood. Disentangling this relation could aid elucidating the mechanisms underlying these traits. The relation between degree of language lateralization and degree of hand-preference was investigated in extended pedigrees with multi-generational left-handedness (n=310). Language lateralization was measured with functional Transcranial Doppler, hand-preference with the Edinburgh Handedness Inventory. Degree of hand-preference did not mirror degree of language lateralization. Instead, the prevalence of right-hemispheric and bilateral language lateralization rises with increasing strength of left-handedness. Degree of hand-preference does not predict degree of language lateralization, thus refuting genetic models in which one mechanism defines both hand-preference and language lateralization. Instead, our findings suggest a model in which increasing strength of left-handedness is associated with increased variation in directionality of cerebral dominance.

Perinatal testosterone exposure and cerebral lateralisation in adult males: evidence for the callosal hypothesis

Two competing theories address the influence of foetal testosterone on cerebral laterality: one proposing exposure to high foetal testosterone concentrations is related to atypical lateralisation (Geschwind-Galaburda hypothesis), the other that high foetal testosterone concentrations exaggerate typical lateralisation (callosal hypothesis). The current study examined the relationship between cord testosterone concentrations and cerebral laterality for language and spatial memory in adulthood. Male participants with high (>0.15nmol) and low (<0.10nmol) cord testosterone levels were invited to take part in the study (n=18 in each group). Cerebral laterality was measured using functional Transcranial Doppler ultrasonography, while participants completed word generation and visual short-term memory tasks. Typical left lateralisation of language was more common in the high-testosterone group than in the low-testosterone group, χ(2)=4.50, df=1, p=034. Spatial memory laterality was unrelated to cord testosterone level. Our findings indicate that foetal testosterone exposure is related to language laterality in a direction that supports the callosal hypothesis.

No population bias to left-hemisphere language in 4-year-olds with language impairment

Background. An apparent paradox in the field of neuropsychology is that people with atypical cerebral lateralization do not appear to suffer any cognitive disadvantage, yet atypical cerebral lateralization is more common in children and adults with developmental language disorders. This study was designed to explore possible reasons for this puzzling pattern of results. Methods. We used functional transcranial Doppler ultrasound (fTCD) to assess cerebral blood flow during language production in 57 four-year-olds, including 15 children who had been late-talkers when first seen at 20 months of age. We categorized cerebral lateralization as left, right or bilateral, and compared proportions with each type of laterality with those seen in a previously tested sample of children aged 6-16 years. We also compared language scores at 4 years for those with typical and atypical lateralization, and then looked at the association the opposite way: comparing those with typical or impaired language in terms of their cerebral lateralization. Results. The distribution of types of cerebral lateralization was similar for 4-year-olds to that seen in older children. Overall, cerebral lateralization was not predictive of language level. However, for children who had language difficulties at 20 months and/or 4 years (N = 21), there was no population bias to left-hemisphere language activation, whereas children without language problems at either age showed a pronounced bias to left-sided language lateralization. Nevertheless, many children with right hemisphere language had no indications of language difficulties, confirming that atypical cerebral asymmetry is not a direct cause of problems. Conclusions. We suggest that atypical lateralization at the individual level is not associated with language impairment. However, lack of lateralization at the population level is a marker of risk for language impairment, which could be due to genetic or non-genetic causes.

Inferring common cognitive mechanisms from brain blood-flow lateralization data: a new methodology for fTCD analysis

Current neuroimaging techniques with high spatial resolution constrain participant motion so that many natural tasks cannot be carried out. The aim of this paper is to show how a time-locked correlation-analysis of cerebral blood flow velocity (CBFV) lateralization data, obtained with functional TransCranial Doppler (fTCD) ultrasound, can be used to infer cerebral activation patterns across tasks. In a first experiment we demonstrate that the proposed analysis method results in data that are comparable with the standard Lateralization Index (LI) for within-task comparisons of CBFV patterns, recorded during cued word generation (CWG) at two difficulty levels. In the main experiment we demonstrate that the proposed analysis method shows correlated blood-flow patterns for two different cognitive tasks that are known to draw on common brain areas, CWG, and Music Synthesis. We show that CBFV patterns for Music and CWG are correlated only for participants with prior musical training. CBFV patterns for tasks that draw on distinct brain areas, the Tower of London and CWG, are not correlated. The proposed methodology extends conventional fTCD analysis by including temporal information in the analysis of cerebral blood-flow patterns to provide a robust, non-invasive method to infer whether common brain areas are used in different cognitive tasks. It complements conventional high resolution imaging techniques.

Investigating language lateralization during phonological and semantic fluency tasks using functional transcranial Doppler sonography

Although there is consensus that the left hemisphere plays a critical role in language processing, some questions remain. Here we examine the influence of overt versus covert speech production on lateralization, the relationship between lateralization and behavioural measures of language performance and the strength of lateralization across the subcomponents of language. The present study used functional transcranial Doppler sonography (fTCD) to investigate lateralization of phonological and semantic fluency during both overt and covert word generation in right-handed adults. The laterality index (LI) was left lateralized in all conditions, and there was no difference in the strength of LI between overt and covert speech. This supports the validity of using overt speech in fTCD studies, another benefit of which is a reliable measure of speech production.

Cerebral lateralization for language in deaf children with cochlear implantation

Functional Transcranial Doppler ultrasonography (fTCD) was used to investigate the effects of early acoustic deprivation and subsequent reafferentation on cerebral dominance for language in deaf children provided with Cochlear Implantation (CI). Twenty children with CI (13 in right ear and 7 in left ear) and 20 controls matched for age, sex and handedness were administered a fTCD animation description task. Left hemisphere dominance for language with comparable mean Laterality Indexes (LIs) was found in children with CI and controls; right-ear implanted subjects showed cerebral activation controlateral to implanted ear more frequently than left-ear implanted ones. Linguistic proficiency of CI recipients was below age expectation in comparison to controls; language scores did not significantly differ between children with left and right LI, whereas both age and side of implantation were significantly related to language outcome. Theoretical implication and potential clinical application of fTCD in CI management are discussed.

Feasibility of transcranial Doppler and single photon emission computed tomography in compound neuroactivation task

The aim of this study was to test feasibility of transcranial Doppler (TCD) and single photon emission computed tomography (SPECT) during compound neuroactivation task. The study was performed in 60 healthy right-handed volunteers. Cerebral blood flow velocity was measured by TCD in both middle cerebral arteries (MCA) at baseline and during computer game. The same stimulus and response pattern was used in 15 subjects that additionally underwent brain SPECT. Percentage differences between measurements were determined through quantitative result assessment. Both methods detected a statistically significant cerebral blood flow increase during neuroactivation. Correlation of TCD and SPECT showed statistically significant correlation only for the increase of cerebral blood flow velocity in the right MCA and for the right-sided cerebral blood flow increase, demonstrating that both methods partially measure similar cerebral blood flow changes that occur during neuroactivation. Comparison of TCD and SPECT showed TCD to be inadequately sensitive method for evaluation of cerebral blood flow during complex activation paradigm.

Shared brain lateralization patterns in language and Acheulean stone tool production: a functional transcranial Doppler ultrasound study

Background

The popular theory that complex tool-making and language co-evolved in the human lineage rests on the hypothesis that both skills share underlying brain processes and systems. However, language and stone tool-making have so far only been studied separately using a range of neuroimaging techniques and diverse paradigms.

Methodology/Principal Findings

We present the first-ever study of brain activation that directly compares active Acheulean tool-making and language. Using functional transcranial Doppler ultrasonography (fTCD), we measured brain blood flow lateralization patterns (hemodynamics) in subjects who performed two tasks designed to isolate the planning component of Acheulean stone tool-making and cued word generation as a language task. We show highly correlated hemodynamics in the initial 10 seconds of task execution.

Conclusions/Significance

Stone tool-making and cued word generation cause common cerebral blood flow lateralization signatures in our participants. This is consistent with a shared neural substrate for prehistoric stone tool-making and language, and is compatible with language evolution theories that posit a co-evolution of language and manual praxis. In turn, our results support the hypothesis that aspects of language might have emerged as early as 1.75 million years ago, with the start of Acheulean technology.

Cerebrovascular response in migraineurs during prophylactic treatment with acupuncture: a randomized controlled trial

OBJECTIVES

The study objective was to evaluate the effect of acupuncture on cerebrovascular response in migraineurs by transcranial Doppler ultrasound.

DESIGN

This study was a randomized, quasi double-blinded, placebo-controlled study.

SUBJECTS

Thirty-five (35) migraineurs were diagnosed according to the International Headache Society criteria. The stimulus paradigm was performed in 18 verum and 17 placebo acupuncture patients.

INTERVENTIONS

Participants were treated with acupuncture according to Traditional Chinese Medicine recommendations. All patients received one session of acupuncture each week for 8 weeks.

OUTCOME MEASURES

To evaluate the clinical effect of acupuncture treatment, headache frequency and intensity was monitored by a headache diary. Cerebral blood flow velocity data were analyzed with a validated technique based on automated stimulus-related averaging. Vasotonus was determined by systolic and mean flow velocities and pulsality index in right and left middle cerebral arteries during rest. Cerebrovascular response was evaluated by detecting the cerebrovascular Valsalva ratio by maximum end-diastolic flow velocity acceleration during the straining phase of a Valsalva maneuver. Additionally, the centroperipheral Valsalva ratio was determined by the quotient of the cerebrovascular ratio to the corresponding blood pressure acceleration.

RESULTS

Pre-/post-acupuncture treatment comparisons between verum- and placebo- acupuncture groups demonstrated a significant decrease of days with migraine headache in the verum group (-52.5%; p<0.001), whereas placebo-acupuncture patients profited to a smaller extent and the duration of headache attack (hours/month) did not decrease significantly. Pretreatment recordings showed increased vasotonus and exaggerated cerebrovascular response in migraineurs. Pre-/post-treatment comparisons demonstrated no significant differences in vasotonus between groups, while cerebrovascular response patterns to Valsalva stimulus were significantly (p<0.001) diminished in verum-acupuncture patients, but not in the placebo group.

CONCLUSIONS

The findings indicate that prophylactic treatment of migraineurs by standardized acupuncture might positively influence the dysfunction of the cerebrovascular response to autonomic stimuli, but not the cerebral vasotonus during rest.

Functional transcranial Doppler assessment of cerebral blood flow velocities changes during attention tasks

BACKGROUND AND PURPOSE

Aim of our study was to evaluate cerebral hemodynamic changes during performance of attention tasks and to correlate them with reaction time (RT) and percentage of right answers.

METHODS

Mean flow velocity (MFV) in middle cerebral arteries was monitored in 30 subjects by transcranial Doppler during tonic alertness, phasic alertness, focused and divided attention tasks.

RESULTS

Mean flow velocity increase was significantly higher during divided attention with respect to other tasks (P < .001). MFV increase was higher in the right than in the left side (P < .001). Asymmetry during attention tasks resulted significantly higher than that observed in tonic alertness condition. RT was increased during focused attention tasks (P < .001 vs. both alert tasks), with further increase during divided attention tasks (P < .001 vs. focused attention task). RT was inversely related to MFV increase only during tonic alertness (P = 0.012 for left side; P = 0.008 for right side). During the divided attention tasks, an association was found between MFV increase and correct answers (r = 0.39, P = 0.033).

CONCLUSIONS

These data show a relationship between RT, correct answers and changes in blood flow velocity and suggest that this method of cerebral blood flow investigation could be a useful approach during assessment of patients with attention deficit.

Methodological aspects of functional transcranial Doppler sonography and recommendations for simultaneous EEG recording

The neurovascular coupling describes a vasoregulative principle of the brain that adapts local cerebral blood flow in accordance with the underlying neuronal activity. It is the basis of modern indirect brain imaging techniques. Because of its wide availability and high tolerability the functional transcranial Doppler has been often used to assess brain function in clinical conditions. In the present paper we will give an overview of the current understanding of the coupling, explain basic principles of the Doppler technique and summarize relevant findings of functional Doppler tests in the different vascular territories of the brain. Finally, the concept of a combined functional electroencephalogram and transcranial Doppler technique will be outlined, which allows simultaneous investigation of the neuronal and vascular responses of neurovascular coupling.

The Measurement of Language Lateralization with Functional Transcranial Doppler and Functional MRI: A Critical Evaluation

Cerebral language lateralization can be assessed in several ways. In healthy subjects, functional MRI (fMRI) during performance of a language task has evolved to be the most frequently applied method. Functional transcranial Doppler (fTCD) may provide a valid alternative, but has been used rarely. Both techniques have their own strengths and weaknesses and as a result may be applied in different fields of research. Until now, only one relatively small study (n = 13) investigated the correlation between lateralization indices (LIs) measured by fTCD and fMRI and showed a remarkably high correlation. To further evaluate the correlation between LIs measured with fTCD and fMRI, we compared LIs of 22 healthy subjects (12 left- and 10 right-handed) using the same word generation paradigm for the fTCD as for the fMRI experiment. LIs measured with fTCD were highly but imperfectly correlated with LIs measured with fMRI (Spearman's rho = 0.75, p < 0.001). The imperfectness of the correlation can partially be explained by methodological restrictions of fMRI as well as fTCD. Our results suggest that fTCD can be a valid alternative for fMRI to measure lateralization, particularly when costs or mobility are important factors in the study design.

Can the language-dominant hemisphere be predicted by brain anatomy?

It has long been suspected that cortical interhemispheric asymmetries may underlie hemispheric language dominance (HLD). To test this hypothesis, we determined interhemispheric asymmetries using stereology and MRI of three cortical regions hypothesized to be related to HLD (Broca's area, planum temporale, and insula) in healthy adults in whom HLD was determined using functional transcranial Doppler sonography and functional MRI (15 left HLD, 10 right HLD). We observed no relationship between volume asymmetry of the gyral correlates of Broca's area or planum temporale and HLD. However, we observed a robust relationship between volume asymmetry of the insula and HLD (p = .008), which predicted unilateral HLD in 88% individuals (86.7% left HDL and 90% right HLD). There was also a subtle but significant positive correlation between the extent of HLD and insula volume asymmetry (p = .02), indicating that a larger insula predicted functional lateralization to the same hemispheric side for the majority of subjects. We found no visual evidence of basic anatomical markers of HLD other than that the termination of the right posterior sylvian fissure was more likely to be vertical than horizontal in right HLD subjects (p = .02). Predicting HLD by virtue of gross brain anatomy is complicated by interindividual variability in sulcal contours, and the possibility remains that morphological and cytoarchitectural organization of the classical language regions may underlie HLD when analyses are not constrained by the natural limits imposed by measurement of gyral volume. Although the anatomical correlates of HLD will most likely be found to include complex intra- and interhemispheric connections, there is the possibility that such connectivity may correlate with gray matter morphology. We suggest that the potential significance of insular morphology should be considered in future studies addressing the anatomical correlates of human language lateralization.