Sulcus topography of the parietal opercular region: an anatomic and MR study

The study describes the sulcal and gyral topography, variability, and left-right asymmetry of the parietal operculum. Eighty postmortem hemispheres as well as sagittal magnetic resonance images from 20 health volunteers (40 hemispheres) were evaluated. Four different types of parietal opercular sulcus topography were recognized. Most frequently, and conforming with the anatomic "textbook pattern", the inferior postcentral sulcus (POCS) is the sulcus anterior to the posterior ascending ramus (PAR) of the Sylvian fissure (type 1). Variations were the following: lack of a PAR (type 2), interposition of an intermediate opercular sulcus and gyrus between PAR and POCS (type 3), and direct transition of PAR into POCS with subsequent lack of a classical supramarginal gyrus (type 4). Inconstancy of the sulcal standard arrangement was especially pronounced among left hemispheres, where the patterns differed from type 1 in one third of the cases. Types 2 and 3 were significantly more frequent in left hemispheres, whereas type 4 occurred significantly more frequently in right hemispheres. Upon intraindividual left-right comparison, a remarkable 38% of the brains showed gross asymmetry of the parietal opercular sulcus patterns, characterized by a left type 2 or 3 and/or a right type 4; another 5% exhibited a reverse type of asymmetry. The findings supplement previous data on gross variability and left-right asymmetry of the posterior Sylvian fissure and its lower bank. They indicate that the Sylvian fissure is an unreliable landmark with respect to inferior parietal structures especially in left hemispheres. Individual mapping of perisylvian topography may contribute to studies on structural-functional relationship.     

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.     

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.     

Left posterior auditory-related cortices participate both in speech perception and speech production: Neural overlap revealed by fMRI

Recent neuroimaging studies and neuropsychological data suggest that there are regions in posterior auditory cortex that participate both in speech perception and speech production. An outstanding question is whether the same neural regions support both perception and production or whether there exist discrete cortical fields subserving these functions. Previous neurophysiological studies suggest that there is indeed regional overlap between these systems, but those studies used a rehearsal task to assess production. The present study addressed this question in an event-related fMRI experiment in which subjects listened to speech and in separate trials, performed a covert object naming task. Single subject analysis revealed regions of coactivation for speech perception and production in the left posterior superior temporal sulcus (pSTS), left area Spt (a region in the Sylvian fissure at the parietal-temporal boundary), and left inferior frontal gyrus. These results are consistent with lesion data and previous physiological data indicating that posterior auditory cortex plays a role in both reception and expression of speech. We discuss these findings within the context of a neuroanatomical framework that proposes these neural sites are a part of an auditory-motor integration system.     

Brain activity varies with modulation of dynamic pitch variance in sentence melody

Fourteen native speakers of German heard normal sentences, sentences which were either lacking dynamic pitch variation (flattened speech), or comprised of intonation contour exclusively (degraded speech). Participants were to listen carefully to the sentences and to perform a rehearsal task. Passive listening to flattened speech compared to normal speech produced strong brain responses in right cortical areas, particularly in the posterior superior temporal gyrus (pSTG). Passive listening to degraded speech compared to either normal or flattened speech particularly involved fronto-opercular and subcortical (Putamen, Caudate Nucleus) regions bilaterally. Additionally the Rolandic operculum (premotor cortex) in the right hemisphere subserved processing of neat sentence intonation. As a function of explicit rehearsing sentence intonation we found several activation foci in the left inferior frontal gyrus (Broca's area), the left inferior precentral sulcus, and the left Rolandic fissure. The data allow several suggestions: First, both flattened and degraded speech evoked differential brain responses in the pSTG, particularly in the planum temporale (PT) bilaterally indicating that this region mediates integration of slowly and rapidly changing acoustic cues during comprehension of spoken language. Second, the bilateral circuit active whilst participants receive degraded speech reflects general effort allocation. Third, the differential finding for passive perception and explicit rehearsal of intonation contour suggests a right fronto-lateral network for processing and a left fronto-lateral network for producing prosodic information. Finally, it appears that brain areas which subserve speech (frontal operculum) and premotor functions (Rolandic operculum) coincidently support the processing of intonation contour in spoken sentence comprehension.     

Neuroanatomical and behavioral asymmetry in an adult compensated dyslexic

Individual differences in cortical anatomy are readily observable, but their functional significance for behaviors such as reading is not well understood. Here, we report a case of an apparent compensated dyslexic who had attained high achievement in visuospatial mathematics. Data from a detailed background interview, psychometric testing, divided visual field tasks measuring basic word recognition (word naming, nonword naming, and lexical decision), and more controlled word retrieval (verb, category, and rhyme generation), and measurements of his atypical brain structure are described. The findings suggested that enhanced "top-down" processing could provide the means to compensate for deficient "bottom-up" word decoding skills in this case. Relative to controls, this individual also evidenced unusually large asymmetries on several divided visual field lexical tasks, an extreme leftward asymmetry of the planum temporale, and a rare form of Sylvian fissure morphology (Steinmetz type 4, [Steinmetz, H., Ebeling, U., Huang, Y., & Kahn, T. (1990). Sulcus topography of the parietal opercular region: An anatomic and MR study. Brain and Language, 38, 515-533.]). We suggest that certain forms of brain organization may be associated with successful behavioral compensation for dyslexia, and that anatomical variations in the right hemisphere may be important contributors to individual differences in reading acquisition and achievement.     

Sylvian fissure and parietal anatomy in children with autism spectrum disorder

Autism spectrum disorder (ASD) is characterized by deficits in social functioning and language and communication, with restricted interests or stereotyped behaviors. Anatomical differences have been found in the parietal cortex in children with ASD, but parietal subregions and associations between Sylvian fissure (SF) and parietal anatomy have not been explored. In this study, SF length and anterior and posterior parietal volumes were measured on MRI in 30 right-handed boys with ASD and 30 right-handed typically developing boys (7-14 years), matched on age and non-verbal IQ. There was leftward SF and anterior parietal asymmetry, and rightward posterior parietal asymmetry, across groups. There were associations between SF and parietal asymmetries, with slight group differences. Typical SF asymmetry was associated with typical anterior and posterior parietal asymmetry, in both groups. In the atypical SF asymmetry group, controls had atypical parietal asymmetry, whereas in ASD there were more equal numbers of individuals with typical as atypical anterior parietal asymmetry. We did not find significant anatomical-behavioral associations. Our findings of more individuals in the ASD group having a dissociation between cortical asymmetries warrants further investigation of these subgroups and emphasizes the importance of investigating anatomical relationships in addition to group differences in individual regions.     

Variability in perisylvian brain anatomy in healthy adults

Gray matter volumes of Heschl's gyrus (HG), planum temporale (PT), pars triangularis (PTR), and pars opercularis were measured on MRI in 48 healthy right-handers. There was the expected leftward PT asymmetry in 70.8%, and leftward PTR asymmetry in 64.6% of the sample. When asymmetry patterns within individuals were examined, there was not one typical pattern, rather several typical configurations were found. In addition, some combinations of asymmetry did not exist in our sample suggesting that some perisylvian anatomical configurations may provide a more suitable neural substrate for the development of language than others. There were also sex differences in HG. Men had rightward asymmetry and women demonstrated leftward asymmetry, due to women having smaller right HG, compared to men.     

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.     

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.     

Focused and Nonfocused Attention in Verbal and Emotional Dichotic Listening: An FMRI Study

Functional magnetic resonance imaging (fMRI) was used to identify cortical regions which are involved in two dichotic listening tasks. During one task the subjects were required to allocate attention to both ears and to detect a specific target word (phonetic task), while during a second task the subjects were required to detect a specific emotional tone (emotional task). During three attentional conditions of each task, the subjects were required to focus attention to the right (FR) or left ear (FL), while during a third condition subjects were required to allocate attention to both ears simultaneously. In 11 right-handed male subjects, these dichotic listening tasks evoked strong activations in a temporofrontal network involving auditory cortices located in the temporal lobe and prefrontal brain regions. Hemodynamic responses were measured in the following regions of interest: Heschl's gyrus (HG), the planum polare (PP), the planum temporale (PT), the anterior superior temporal sulcus (aSTS), the posterior superior temporal sulcus (pSTS), and the inferior frontal gyrus region (IFG) of both hemispheres. The following findings were obtained: (1) the degree of activation in HG and PP depends on the direction of attention. In particular it was found that selectively attending to right-ear input led to increased activity specifically in the left HG and PP and attention to left ear input increased right-sided activity in these structures; (2) hemodynamic responses in the PT, aSTS, pSTS, and IFG were not modulated by the different focused-attention conditions; (3) hemodynamic responses in HG and PP in the nonforced conditions were the sum activation of the forced conditions; (4) there was no general difference between the phonetic and emotion tasks in terms of hemodynamic responses; (5) hemodynamic responses in the PT and pSTS were strongly left-lateralized, reflecting the specialization of these brain regions for language processing. These findings are discussed in the context of current theories of hemispheric specialization.     

Dorsal and ventral streams: a framework for understanding aspects of the functional anatomy of language

Despite intensive work on language-brain relations, and a fairly impressive accumulation of knowledge over the last several decades, there has been little progress in developing large-scale models of the functional anatomy of language that integrate neuropsychological, neuroimaging, and psycholinguistic data. Drawing on relatively recent developments in the cortical organization of vision, and on data from a variety of sources, we propose a new framework for understanding aspects of the functional anatomy of language which moves towards remedying this situation. The framework posits that early cortical stages of speech perception involve auditory fields in the superior temporal gyrus bilaterally (although asymmetrically). This cortical processing system then diverges into two broad processing streams, a ventral stream, which is involved in mapping sound onto meaning, and a dorsal stream, which is involved in mapping sound onto articulatory-based representations. The ventral stream projects ventro-laterally toward inferior posterior temporal cortex (posterior middle temporal gyrus) which serves as an interface between sound-based representations of speech in the superior temporal gyrus (again bilaterally) and widely distributed conceptual representations. The dorsal stream projects dorso-posteriorly involving a region in the posterior Sylvian fissure at the parietal-temporal boundary (area Spt), and ultimately projecting to frontal regions. This network provides a mechanism for the development and maintenance of "parity" between auditory and motor representations of speech. Although the proposed dorsal stream represents a very tight connection between processes involved in speech perception and speech production, it does not appear to be a critical component of the speech perception process under normal (ecologically natural) listening conditions, that is, when speech input is mapped onto a conceptual representation. We also propose some degree of bi-directionality in both the dorsal and ventral pathways. We discuss some recent empirical tests of this framework that utilize a range of methods. We also show how damage to different components of this framework can account for the major symptom clusters of the fluent aphasias, and discuss some recent evidence concerning how sentence-level processing might be integrated into the framework.     

音乐绝对音高信息加工的脑机制

音乐绝对音高(absolute pitch, AP)一直是音乐心理学者感兴趣的问题。AP能力是一种特殊的音乐能力。ERP研究表明具有AP能力的群体只需较少的认知资源进行音高加工, 同时不同AP能力的加工机制也不同; 功能神经成像研究表明大脑左侧额叶背侧后部和左侧颞叶平面对AP加工发挥重要作用; 脑结构研究发现AP群体的某些脑区皮层厚度低于没有绝对音高能力(Non-AP)群体, 这可能与AP特殊的加工机制有关。AP能力形成需要先天遗传和后天环境的共同作用, 其相互作用的脑机制需结合行为遗传学的研究方法及成果。     

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.     

Gyral morphology in the posterior Sylvian region in families affected by developmental language disorder

This study describes the family aggregation of gyral morphology in the posterior perisylvian region in families that contain one or more children with a developmental language disorder. The probands in these families were 8 male and 2 female children referred through therapy programs and schools for children with language and reading problems. Family members included both biological parents (10 m, 10 f) and all available siblings (6 m, 4 f). Gyral morphology in the members of these families was compared with control subjects (10 m, 10 f) who were without a personal or family history of developmental language disorders. Gyral morphology was evaluated using T1-weighted sagittal scans from a GE Signa 1.5T magnet, 5 mm consecutive slices through the full brain volume. A less common type of Sylvian fissure morphology was more frequently found in the hemispheres of language-disordered subjects and their first-degree relatives than in control subjects. In addition, the pattern of Sylvian fissure morphology across generations within the families suggests that this feature might be inherited from either parent. The elevated rate of extra gyri in the posterior perisylvian region in families affected by language disorder links an anomaly within a language-related brain region with familial risk for this disorder.     

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.     

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。     

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.     

Structural imaging in dyslexia: the planum temporale

The search for a neurobiological substrate for dyslexia has focused on anomalous planum symmetry. The results of imaging studies of the planum have been inconsistent, perhaps due to diagnostic uncertainty, technical differences in measurement criteria, and inadequate control of handedness, sex, and cognitive ability. Although structural imaging studies have not clarified the neurobiology of reading disability, converging evidence suggests that variation in asymmetry of the planum temporale does have functional significance. Studies in a variety of populations have shown a significant association between planar asymmetry, the strength of hand preference, and general verbal skills such as vocabulary and comprehension. Future structural imaging studies of dyslexia should match participants on hand preference and general verbal ability in order to determine the relationship between brain structure and written and oral language.     

Articulatory/phonetic sequencing at the level of the anterior perisylvian cortex: a functional magnetic resonance imaging (fMRI) study

Damage to the anterior peri-intrasylvian cortex of the dominant hemisphere may give rise to a fairly consistent syndrome of articulatory deficits in the absence of relevant paresis of orofacial or laryngeal muscles (apraxia of speech, aphemia, or phonetic disintegration). The available clinical data are ambiguous with respect to the relevant lesion site, indicating either dysfunction of the premotor aspect of the lower precentral gyrus or the anterior insula in the depth of the Sylvian fissure. In order to further specify the functional anatomic substratum of this syndrome, functional magnetic resonance imaging (fMRI) was performed during reiteration of syllables differing in their demands on articulatory/phonetic sequencing (CV versus CCCV versus CVCVCV). Horizontal tongue movements and a polysyllabic lexical item served as control conditions. Repetition of the CV and CCCV monosyllables elicited a rather bilateral symmetric hemodynamic response at the level of the anterior and posterior bank of the central sulcus (primary sensorimotor cortex), whereas a more limited area of neural activity arose within this domain during production of lexical and nonlexical polysyllables, significantly or exclusively lateralized toward the left hemisphere. There is neurophysiological evidence that primary sensorimotor cortex mediates the "fractionation" of movements. Assuming that the polysyllables considered are organized as coarticulated higher-order units, the observed restricted and lateralized cortical activation pattern, most presumably, reflects a mode of "nonindividualized" motor control posing fewer demands on "movement fractionation." These findings may explain the clinical observation of disproportionately worse repetition of trisyllabic items as compared to monosyllables in apraxia of speech. The various test materials failed to elicit significant activation of the anterior insula. If at all, only horizontal tongue movements yielded a hemodynamic reaction extending beyond the sensorimotor cortex to premotor areas. Since limbic projections target the inferior dorsolateral frontal lobe, the enlarged region of activation during horizontal tongue movements might reflect increased attentional requirements of this task.