Dyslexia, Neurolinguistic Ability, and Anatomical Variation of the Planum Temporale

This article addresses the relationship between patterns of planum temporale symmetry/asymmetry and dyslexia and neurolinguistic abilities. Considerable research indicates that dyslexic individuals typically do not display the predominant pattern of leftward planum temporale asymmetry. Variable findings on the structural basis of symmetry are due partially to measurement issues, which are examined in some detail in this critical review. The physiological basis of symmetry may be reduced neuronal elimination in the right planum, although other alternatives are offered. Theories are offered to explain how symmetrical plana are related to dyslexia, and it is evident that symmetrical plana are not sufficient to produce dyslexia. However, some evidence suggests that nonleftward plana asymmetry is associated with deficits in verbal comprehension, phonological decoding, and expressive language. It is concluded that nonleftward asymmetry is associated with linguistic deficits, but that explanatory theories need to be further developed. Among the many issues that need to be addressed, future research needs to determine whether the relationship between patterns of planum temporale symmetry/asymmetry and linguistic ability is specific to dyslexia or if asymmetry covaries lawfully with linguistic abilities in nondyslexic populations.     

Child Age and Planum Temporale Asymmetry

Investigations using in vivo magnetic resonance (MR) morphometry have shown that left-right asymmetry of the planum temporale (PT) is a structural correlate of hemispheric functional asymmetries in adult humans (e.g., handedness, language representation). Postmortem studies of brains of fetuses and newborns have demonstrated that PT asymmetry becomes visible as early as in the last gestational trimester. The same studies could not clarify when the full (adult) degree of PT asymmetry is reached during brain development and whether this process may be influenced by functional specialization during childhood. We examined 61 neuropsychiatrically normal right-handed children aged 3 to 14 years (mean age +/-SD, 8.4 +/- 2. 7 years; cross-sectional study). MR morphometry showed no change in PT or planum parietale asymmetry with increasing age or brain volume. An unexpected gender difference of unknown significance emerged, with girls displaying a stronger leftward PT asymmetry, independently of age. For the age range studied, the results suggest that functional differentiation follows a structural asymmetry that is already "preset." Copyright 1999 Academic Press.     

Cerebral Organization of Motor Programming and Verbal Processing as a Function of Degree of Hand Preference and Familial Sinistrality

Seventy-six right- and left-handed subjects responded to monaurally presented verbal stimuli (CVs) using their right and left hands on separate occasions. Both degree of hand preference and familial sinistrality (FS) were taken into account. It was found that, contrary to expectation, the manual response interfered with the verbal perception task, but only in the consistent strong handers. The pattern of interference suggests that those with a consistent hand preference (right or left) have general motor programming in the left hemisphere. Those with an inconsistent strong hand preference probably have some degree of general motor programming in both hemispheres. No effect for FS was found for the lateralization of verbal processing or general motor programming.     

MRI evaluation of the size and symmetry of the planum temporale in adolescents with developmental dyslexia

MRI technique was used to examine the size and symmetry of the plana temporale in 19 dyslexic students in grade 8 and in carefully matched control subjects. The results demonstrated a high frequency of planum symmetry among the dyslexics (70%) whereas symmetry was observed in only 30% of the control subjects. It was not possible to demonstrate any clear association between symmetry/asymmetry of planum temporale and handedness. Word-reading strategies among the dyslexics and control subjects were investigated with computerized tasks where accuracy and naming latency were recorded. All subjects with pure phonological deficits in reading had symmetrical plana temporale indicating a possible neuroanatomical basis for a characteristic symptom of linguistic processing deficiency in developmental dyslexia.     

Uncoupled leftward asymmetries for planum morphology and functional language processing

Explanations for left hemisphere language laterality have often focused on hemispheric structural asymmetry of the planum temporale. We examined the association between an index of language laterality and brain morphology in 99 normal adults whose degree of laterality was established using a functional MRI single-word comprehension task. The index of language laterality was derived from the difference in volume of activation between the left and right hemispheres. Planum temporale and brain volume measures were made using structural MRI scans, blind to the functional data. Although both planum temporale asymmetry (t(1,99) = 6.86, p < .001) and language laterality (t(1,99) = 15.26, p < .001) were significantly left hemisphere biased, there was not a significant association between these variables (r(99) = .01,ns). Brain volume, a control variable for the planum temporale analyses, was related to language laterality in a multiple regression (beta = -.30, t = -2.25, p < .05). Individuals with small brains were more likely to demonstrate strong left hemisphere language laterality. These results suggest that language laterality is a multidimensional construct with complex neurological origins.     

Atypical speech lateralization in adults with developmental coordination disorder demonstrated using functional transcranial Doppler ultrasound

Research using clinical populations to explore the relationship between hemispheric speech lateralization and handedness has focused on individuals with speech and language disorders, such as dyslexia or specific language impairment (SLI). Such work reveals atypical patterns of cerebral lateralization and handedness in these groups compared to controls. There are few studies that examine this relationship in people with motor coordination impairments but without speech or reading deficits, which is a surprising omission given the prevalence of theories suggesting a common neural network underlying both functions. We use an emerging imaging technique in cognitive neuroscience; functional transcranial Doppler (fTCD) ultrasound, to assess whether individuals with developmental coordination disorder (DCD) display reduced left‐hemisphere lateralization for speech production compared to control participants. Twelve adult control participants and 12 adults with DCD, but no other developmental/cognitive impairments, performed a word‐generation task whilst undergoing fTCD imaging to establish a hemispheric lateralization index for speech production. All participants also completed an electronic peg‐moving task to determine hand skill. As predicted, the DCD group showed a significantly reduced left lateralization pattern for the speech production task compared to controls. Performance on the motor skill task showed a clear preference for the dominant hand across both groups; however, the DCD group mean movement times were significantly higher for the non‐dominant hand. This is the first study of its kind to assess hand skill and speech lateralization in DCD. The results reveal a reduced leftwards asymmetry for speech and a slower motor performance. This fits alongside previous work showing atypical cerebral lateralization in DCD for other cognitive processes (e.g., executive function and short‐term memory) and thus speaks to debates on theories of the links between motor control and language production.     

Lateralization of cognitive processes in the brain

The lateralization of cognitive processes in the brain is discussed. The traditional view of a language-visuo/spatial dichotomy of function between the hemispheres has been replaced by more subtle distinctions. The use of magnetic resonance imaging (MRI) to study brain morphology has resulted in a renewed focus on the relationship between structural and functional asymmetry. Focus has been on the role played by the planum temporale area in the posterior part of the superior temporal gyrus for language asymmetry, and the possible significance of the larger left planum. The dichotic listening technique is used to illustrate the difference between bottom-up, or stimulus-driven laterality versus top-down, or instruction-driven laterality. It is suggested that the hemispheric dominance observed at any time is the sum result of the dynamic interaction between bottom-up and top-down processing tendencies. Stimulus-driven laterality dominance is always monitored and modulated through top-down cognitive processes, like shifting of attention and changes in arousal. A model of top-down modulation of bottom-up laterality is presented with special reference to the understanding of psychiatric disorders.     

Unilateral implicit motor learning deficit in developmental dyslexia

It has been suggested that developmental dyslexia involves various literacy, sensory, motor skill, and processing speed deficits. Some recent studies have shown that individuals with developmental dyslexia exhibit implicit motor learning deficits, which may be related to cerebellar functioning. However, previous studies on implicit motor learning in developmental dyslexics have produced conflicting results. Findings from cerebellar lesion patients have shown that patients' implicit motor learning performance varied when different hands were used to complete tasks. This suggests that dyslexia may have different effects on implicit motor learning between the two hands if cerebellar dysfunction is involved. To specify this question, we used a one-handed version of a serial reaction time task to compare the performance of 27 Chinese children with developmental dyslexics with another 27 age-matched children without reading difficulties. All the subjects were students from two primary schools, Grades 4 to 6. The results showed that children with developmental dyslexic responded more slowly than nondyslexic children, and exhibited no implicit motor learning in the condition of left-hand response. In contrast, there was no significant difference in reaction time between two groups of children when they used the right hand to respond. This finding indicates that children with developmental dyslexia exhibited normal motor skill and implicit motor learning ability provided the right hand was used. Taken together, these results suggested that Chinese children with developmental dyslexia exhibit unilateral deficits in motor skill and implicit motor learning in the left hand. Our findings lend partial support to the cerebellar deficit theory of developmental dyslexia.     

Cerebellar tasks do not distinguish between children with developmental dyslexia and children with intellectual disability.

This paper explored the claim that only children with developmental dyslexia, whose reading ability is discrepant from their average general reasoning ability show specific deficits in motor tasks assessing cerebellar functioning (Fawcett et al., 2001, Cerebellar tests differentiate between groups of poor readers with and without IQ discrepancy. J. Learning Disabilities, 34, 119) and rapid serial naming (RAN, Wolf & Bowers, 1999, The double deficit hypothesis for the developmental dyslexias. J. Educ. Psychol., 91, 1). All available children between the ages of 11 and 14 were recruited from two special schools for children with either (a) formally-diagnosed intellectual disabilities (N = 18); or (b) formal diagnoses of developmental dyslexia (N = 25). These two groups of children did not differ on gender, age, pseudoword decoding abilities, or on 7 of 8 literacy measures, but did differ significantly, as expected on verbal and non-verbal reasoning tasks. Importantly, there were no deficits in bead threading ability or postural stability in the children with developmental dyslexia compared to the children with intellectual disabilities. There were also no between-group differences in rapid naming measures. The present results therefore provide no support for the claim that cerebellar deficits or RAN distinguish between children with dyslexia and children with intellectual disabilities that include reading.     

Variability in the anatomy of the planum temporale and posterior ascending ramus: do right- and left handers differ?

The anatomy of the planum temporale (PT) and posterior ascending ramus (PAR) was studied in vivo in 67 healthy right- and left-handed adults using MRI-based morphometry. The left PT was significantly larger than the right, and there was a weakly significant effect of the right PAR larger than the left. A leftward PT asymmetry was found in 72%, and a rightward PAR asymmetry was found in 64% of the sample. The "typical" configuration of a larger left PT and larger right PAR co-occurred in 56% of the subjects studied, which was only slightly more often than predicted by chance. Eight of 67 subjects had "reversed" PT and PAR asymmetries, with consistent left and mixed handers over-represented in this group. Right PAR size was the only variable that predicted writing hand, and left PT size was the only measure that differed by sex. The left PT was expanded relative to the left PAR in 93% of the sample, suggesting that this configuration may be developmentally regulated and may be a critical substrate for the development of language. These findings demonstrate that important relationships exist between hand preference, and the anatomy of posterior cortical language areas.     

The relationship between perisylvian morphology and verbal short-term memory functioning in children with neurodevelopmental disorders

Although children with neurodevelopmental disorders frequently present with reduced short-term memory functioning, the relationship between perisylvian morphology and verbal short-term memory functioning has received limited attention. Thus, examining this relationship in children with neurodevelopmental disorders was the focus of this exploratory study. Results suggested leftward asymmetry in the temporal bank of the planum temporale is related to better coding and storage of semantic material. In contrast, parietal bank morphology is related to coding and storage of phonological material, and presence of an extra gyrus in the parietal region is associated with reduced phonological working memory. Data also supported a relationship between pars triangularis morphology and verbal short-term memory functioning, but this is not material-specific.     

Dyslexia and brain morphology

Although the neurological basis of dyslexia has long been assumed, little direct evidence documents a relation between deviations in brain morphology and behavioral correlates of dyslexia. This article reviews two sources of evidence. Results of CT/MRI studies suggest that in the brains of dyslexics there is an increased incidence of symmetry in the region of the planum temporale and parietooccipital cortex that may be associated with language delay and handedness. Postmortem/cytoarchitectonic studies document symmetry of the plana, provide evidence of thalamic involvement, and chart widely distributed focal dysplasias preferentially involving the left frontal, left temporal, and right frontal regions. Methodological deficiencies characterize this literature, however, particularly regarding the diagnosis of dyslexia, appraisal of handedness and neurolinguistic deficits, and a failure to provide evidence that this pattern of involvement is unique to the dyslexic syndrome. These findings are discussed as they relate to neurobiological theory.     

Shift of manual preference in right-handers following unimanual practice

The effect of unimanual practice of the non-preferred hand on manual asymmetry and manual preference for sequential finger movements was evaluated in right-handers before, immediately after, and 30 days following practice. The results demonstrate that unimanual practice induced a persistent shift of manual preference for the experimental task in most participants, but no significant correlation between manual asymmetry and manual preference was detected. These findings are explained by proposing that manual preference is influenced by a task-specific confidence developed from the recent history of differential use of the limbs, in interaction with a generalized confidence on a single hand for performance of motor skills.     

Cerebral lateralization, preferred cognitive mode, and reading ability in normal children

In a sample of 105 children (aged 6 to 12), a stylistic preference for a verbal approach to problem-solving correlated positively with reading ability (independently of age) and degree of right-ear advantage in the report of dichotic stop consonant-vowel syllables (but not with verbal intelligence or hand preference). Verbal strategic preference may: (1) foster the acquisition of reading skill, and (2) bias attention toward input from the right by generating differential left-hemisphere activation.     

Imbalanced word-reading profiles in eighth-graders

This current study introduced a new method to investigate the prevalence and correlates of significant imbalances in the relative accuracy with which eighth-graders read nonwords (e.g., prauma) and exception words (e.g., vaccine). Substantial proportions of students showed imbalanced word-reading profiles, but these were not strongly tied to differences in reading and spelling achievement. Of the students without reading difficulties, 19% had imbalanced word-reading profiles favoring exception words and 17% had imbalanced word-reading profiles favoring nonwords. Of the poor readers, 39% met the criterion for phonological dyslexia (with imbalanced word-reading profiles favoring exception words) and 14% met the criterion for surface dyslexia (with imbalanced word-reading profiles favoring nonwords) in relation to the eighth-grade benchmark readers, but the incidence of these types of dyslexia varied with verbal ability. Of the poor readers with normal verbal ability, 60% were classified as phonological dyslexics and none was classified as surface dyslexic. In students low in verbal ability, surface dyslexia was more common. However, when imbalanced word-reading profiles were defined in relation to fourth-grade reading-level controls, only 12 phonological dyslexics and 1 surface dyslexic were identified. Relatively few cases of either type of developmental dyslexia appeared to be "pure."     

Hand preference for writing and associations with selected demographic and behavioral variables in 255,100 subjects: the BBC internet study

In an Internet study unrelated to handedness, 134,317 female and 120,783 male participants answered a graded question as to which hand they preferred for writing. This allowed determination of hand preference patterns across 7 ethnic groups. Sex differences in left-handedness were found in 4 ethnic groups, favoring males, while no significant sex differences were found in three of the groups. Prevalence of left-handedness in the largest of the ethnic groups (self-labelled as "White") was comparable to contemporary hand preference data for this group [Gilbert, A. N., & Wysocki, C. J. (1992). Hand preference and age in the United states. Neuropsychologia, 30, 601-608] but the prevalence of left-handedness in individuals >70 years of age was considerably higher in the present study. Individuals who indicated "either" hand for writing preference had significantly lower spatial performance (mental rotation task) and significantly higher prevalence of hyperactivity, dyslexia, asthma than individuals who had clear left or right hand preferences, in support of Crow et al. [Crow, T., Crow, L., Done, D., & Leask, S. (1998). Relative hand skill predicts academic ability: global deficits at the point of hemispheric indecision. Neuropsychologia, 36, 1275-1282]. Similarly, an association of writing hand preference and non-heterosexual orientation was clearest for individuals with "either" writing hand responses. We conclude that contradictions in the literature as to whether or not these variables are linked to handedness stem largely from different definitions of hand preference. Due to a lack of statistical power in most studies in the literature, the "either" hand writing preference group that yielded the most salient results in this study is not normally available for analysis.     

绝对音高加工的认知神经机制

绝对音高(absolute pitch,AP)是一种比较罕见的音高加工能力,具有特殊的认知和神经机制。事件相关电位研究表明AP音乐家进行音高命名时,工作记忆参与较少但涉及多个认知策略。功能神经成像研究发现左侧额叶背侧后部和左侧颞叶平面对AP音乐家非常重要,而准AP音乐家(quasi-AP)的某些右侧脑区的参与则反映其增加的音高加工负荷和难度。结构神经成像研究发现AP音乐家具有特殊的灰质结构形态及白质连接。未来研究有待将AP能力进一步分为"具有相对音高能力"与"没有相对音高能力"两类并观察相应的认知神经机制,并通过影像基因组学来探索基因多态性对AP能力的影响,以及有必要观察以声调语言为母语的音乐家进行音高加工的神经机制。     

Longitudinal stability of pre‐reading skill profiles of kindergarten children: implications for early screening and theories of reading

Research suggests that early identification of developmental dyslexia is important for mitigating the negative effects of dyslexia, including reduced educational attainment and increased socioemotional difficulties. The strongest pre‐literacy predictors of dyslexia are rapid automatized naming (RAN), phonological awareness (PA), letter knowledge, and verbal short‐term memory. The relationship among these constructs has been debated, and several theories have emerged to explain the unique role of each in reading ability/disability. Furthermore, the stability of identification of risk based on these measures varies widely across studies, due in part to the different cut‐offs employed to designate risk. We applied a latent profile analysis technique with a diverse sample of 1215 kindergarten and pre‐kindergarten students from 20 schools, to investigate whether PA, RAN, letter knowledge, and verbal short‐term memory measures differentiated between homogenous profiles of performance on these measures. Six profiles of performance emerged from the data: average performers, below average performers, high performers, PA risk, RAN risk, and double‐deficit risk (both PA and RAN). A latent class regression model was employed to investigate the longitudinal stability of these groups in a representative subset of children (n = 95) nearly two years later, at the end of 1st grade. Profile membership in the spring semester of pre‐kindergarten or fall semester of kindergarten was significantly predictive of later reading performance, with the specific patterns of performance on the different constructs remaining stable across the years. There was a higher frequency of PA and RAN deficits in children from lower socioeconomic status (SES) backgrounds. There was no evidence for the IQ–achievement discrepancy criterion traditionally used to diagnose dyslexia. Our results support the feasibility of early identification of dyslexia risk and point to the heterogeneity of risk profiles. These findings carry important implications for improving outcomes for children with dyslexia, based on more targeted interventions.     

Relations among hand preference,craniofacial asymmetry,and ear advantage in young subjects

The relations for hand preference with craniofacial asymmetry and ear advantage, and between craniofacial asymmetry and ear advantage were investigated in young healthy subjects. Ear advantage was recorded as duration of hearing, craniofacial asymmetry by computerized tomography in 44 right-handed and 38 left-handed male and female high school students. Right-handers had a right ear advantage and a larger left craniofacial region, whereas left-handers had a left ear advantage and a larger right craniofacial region. These results are consistent with the speculation that hand preference may be related to craniofacial and consequently aural asymmetries.     

发展性阅读障碍视听时间整合缺陷可能的机制：视听时间再校准能力受损

发展性阅读障碍的本质一直是研究者争论的焦点。大量研究发现, 阅读障碍者具有视听时间整合缺陷。然而, 这些研究仅考察了阅读障碍者视听时间整合加工的整体表现, 也就是平均水平的表现, 却对整合加工的变化过程缺乏探讨。视听时间再校准反映了视听时间整合的动态加工过程, 对内部时间表征与感觉输入之间差异的再校准困难则会导致多感觉整合受损, 而阅读障碍者的再校准相关能力存在缺陷。因此, 视听时间再校准能力受损可能是发展性阅读障碍视听时间整合缺陷的根本原因。未来的研究需要进一步考察发展性阅读障碍者视听时间再校准能力的具体表现, 以及这些表现背后的认知神经机制。