Cerebral asymmetry: motoring on

I argue that the phylogenetic and neurobiological bases for cerebral asymmetry in humans are likely to be found in motor systems rather than in perceptual systems. Current genetic models of human laterality suggest that a `dextral' allele might be responsible for right-handedness and left-cerebral dominance for speech in the majority of humans. The linking of handedness with language lateralization might reflect the early evolution of language as predominantly a system of manual gestures, perhaps switching to a mainly vocal system only with the emergence of Homo sapiens. So-called `mirror neurons' in the prefrontal cortex of the monkey, which fire both when the animal makes a grasping response and when it sees the same response performed by others, might be part of a circuit that is the precursor to language circuits in the brain. This circuit appears to be bilateral in monkeys, but left-hemispheric in humans.     

Listening to language at birth: evidence for a bias for speech in neonates

The nature and origin of the human capacity for acquiring language is not yet fully understood. Here we uncover early roots of this capacity by demonstrating that humans are born with a preference for listening to speech. Human neonates adjusted their high amplitude sucking to preferentially listen to speech, compared with complex non-speech analogues that controlled for critical spectral and temporal parameters of speech. These results support the hypothesis that human infants begin language acquisition with a bias for listening to speech. The implications of these results for language and communication development are discussed. For a commentary on this article see Rosen and Iverson (2007).     

运动、语言和学习：小脑的功能磁共振成像研究

对小脑功能的认识在过去的100年里经历了缓慢而稳定的发展。在最近20年,随着活体神经影像技术尤其是功能磁共振成像（fMRI）的出现,这一领域取得了更加显著的进展。文章简要总结了我们最近关于小脑的fMRI研究,考察了该结构在运动、语言和学习任务中的作用;并通过回顾相关文献,讨论了这些研究的理论意义。小脑的功能本质似乎是一般性的而非通道特异的,动态的而非静态的,联系的而非孤立的。作者提出,研究小脑与大脑之间的相互作用和合作机制将是小脑研究领域的新的生长点     

The specificity of the neural response to speech at birth

In this work we ask whether at birth, the human brain responds uniquely to speech, or if similar activation also occurs to a non‐speech surrogate ‘language’. We compare neural activation in newborn infants to the language heard in utero (English), to an unfamiliar language (Spanish), and to a whistled surrogate language (Silbo Gomero) that, while used by humans to communicate, is not speech. Anterior temporal areas of the neonate cortex are activated in response to both familiar and unfamiliar spoken language, but these classic language areas are not activated to the whistled surrogate form. These results suggest that at the time human infants emerge from the womb, the neural preparation for language is specialized to speech.     

Neural modeling and imaging of the cortical interactions underlying syllable production

This paper describes a neural model of speech acquisition and production that accounts for a wide range of acoustic, kinematic, and neuroimaging data concerning the control of speech movements. The model is a neural network whose components correspond to regions of the cerebral cortex and cerebellum, including premotor, motor, auditory, and somatosensory cortical areas. Computer simulations of the model verify its ability to account for compensation to lip and jaw perturbations during speech. Specific anatomical locations of the model's components are estimated, and these estimates are used to simulate fMRI experiments of simple syllable production.     

WHY A BRAIN CAPABLE OF LANGUAGE EVOLVED ONLY ONCE: PREFRONTAL CORTEX AND SYMBOL LEARNING

Abstract. Language and information processes are critical issues in scientific controversies regarding the qualities that epitomize humanness. Whereas some theorists claim human mental uniqueness with regard to language, others point to successes in teaching language skills to other animals. However, although these animals may learn names for things, they show little ability to utilize a complex framework of symbolic reference. In such a framework, words or other symbols refer not only to objects and concepts but also to sequential and hierarchical relationships with other symbols. This process is essential to human mental operations, including language, mathematics, and music. In humans, these operations may have coevolved with the prefrontal area of the cerebral cortex, which is proportionately much larger in humans than in other animals and more intricately linked with other areas of the brain. Analysis of the structure and function of the prefrontal area suggests that it is centrally involved in the operation of higher-order associative relationships involving the subordination of one set of associations to another. This alternate learning strategy apparently appeared at the cost of certain sensory, motor, or limbic abilities. The payoff was symbolic thinking. Humans thus are unique among species, not just for their highly developed language ability but for their odd style of thinking and learning.     

Spoken language and arm gestures are controlled by the same motor control system

Arm movements can influence language comprehension much as semantics can influence arm movement planning. Arm movement itself can be used as a linguistic signal. We reviewed neurophysiological and behavioural evidence that manual gestures and vocal language share the same control system. Studies of primate premotor cortex and, in particular, of the so-called "mirror system", including humans, suggest the existence of a dual hand/mouth motor command system involved in ingestion activities. This may be the platform on which a combined manual and vocal communication system was constructed. In humans, speech is typically accompanied by manual gesture, speech production itself is influenced by executing or observing transitive hand actions, and manual actions play an important role in the development of speech, from the babbling stage onwards. Behavioural data also show reciprocal influence between word and symbolic gestures. Neuroimaging and repetitive transcranial magnetic stimulation (rTMS) data suggest that the system governing both speech and gesture is located in Broca's area. In general, the presented data support the hypothesis that the hand motor-control system is involved in higher order cognition.     

Mirror Neurons and the Evolution of Embodied Language

ABSTRACT— Mirror neurons are a class of neurons first discovered in the monkey premotor cortex that activate both when the monkey executes an action and when it observes the same action made by another individual. These neurons enable individuals to understand actions performed by others. Two subcategories of mirror neurons in monkeys activate when they listen to action sounds and when they observe communicative gestures made by others, respectively. The properties of mirror neurons could constitute a substrate from which more sophisticated forms of communication evolved; this would make sense, given the anatomical and functional homology between part of the monkey premotor cortex and Broca's area (the "speech" area of the brain) in humans. We hypothesize that several components of human language, including some aspects of phonology and syntax, could be embedded in the organizational properties of the motor system and that a deeper knowledge of this system could shed light on how language evolved.     

Functional Topography of the Cerebellum in Verbal Working Memory

Speech—both overt and covert—facilitates working memory by creating and refreshing motor memory traces, allowing new information to be received and processed. Neuroimaging studies suggest a functional topography within the sub-regions of the cerebellum that subserve verbal working memory. Medial regions of the anterior cerebellum support overt speech, consistent with other forms of motor execution such as finger tapping, whereas lateral portions of the superior cerebellum support speech planning and preparation (e.g., covert speech). The inferior cerebellum is active when information is maintained across a delay, but activation appears to be independent of speech, lateralized by modality of stimulus presentation, and possibly related to phonological storage processes. Motor (dorsal) and cognitive (ventral) channels of cerebellar output nuclei can be distinguished in working memory. Clinical investigations suggest that hyper-activity of cerebellum and disrupted control of inner speech may contribute to certain psychiatric symptoms.     

A cortical circuit for voluntary laryngeal control: Implications for the evolution language

The development of voluntary laryngeal control has been argued to be a key innovation in the evolution of language. Part of the evidence for this hypothesis comes from neuroscience. For example, comparative research has shown that humans have direct cortical innervation of motor neurons controlling the larynx, whereas nonhuman primates do not. Research on cortical motor control circuits has shown that the frontal lobe cortical motor system does not work alone; it is dependent on sensory feedback control circuits. Thus, the human brain must have evolved not only the required efferent motor pathway but also the cortical circuit for controlling those efferent signals. To fill this gap, I propose a link between the evolution of laryngeal control and neuroscience research on the human dorsal auditory-motor speech stream. Specifically, I argue that the dorsal stream Spt (Sylvian parietal-temporal) circuit evolved in step with the direct cortico-laryngeal control pathway and together represented a key advance in the evolution of speech. I suggest that a cortical laryngeal control circuit may play an important role in language by providing a prosodic frame for speech planning.     

Cerebellar output: motor and cognitive channels

The input to the cerebellum has long been known to originate from widespread regions of the cerebral cortex including the frontal, parietal and temporal lobes. The output of the cerebellum, however, was thought to project mainly to the primary motor cortex. Recent anatomical observations have challenged this view. It is now apparent that cerebellar output goes to multiple cortical areas, including not only the primary motor cortex, but also areas of premotor and prefrontal cortex. In fact, there is growing evidence that each of the areas of cerebral cortex that project to the cerebellum is also the target of cerebellar output. The cerebellar output to individual cortical areas originates from distinct clusters of neurons in the deep nuclei which we have termed `output channels'. The individual output channels to the cortical areas we have examined display little or no overlap. Physiological recordings in awake trained primates indicate that neurons in different output channels appear to be involved in distinct aspects of behavior, and in both motor and cognitive functions. These observations indicate that the cerebellar influence on the cerebral cortex is more extensive than previously recognized.     

High neuromagnetic activation in the left prefrontal and frontal cortices correlates with better memory performance for abstract words

The ability to store and manipulate online information may be enhanced by an inner speech mechanism that draws upon motor brain regions. Neural correlates of this mechanism were examined using event-related functional magnetic resonance imaging (fMRI). Sixteen participants completed two conditions of a verbal working memory task. In both conditions, participants viewed one or two target letters. In the “storage” condition, these targets were held in mind across a delay. Then a probe letter was presented, and participants indicated by button press whether the probe matched the targets. In the “manipulation” condition, participants identified new targets by thinking two alphabetical letters forward of each original target (e.g., f → h). Participants subsequently indicated whether the probe matched the newly derived targets. Brain activity during the storage and manipulation conditions was examined specifically during the delay phase in order to directly compare manipulation versus storage processes. Activations that were common to both conditions, yet disproportionately greater with manipulation, were observed in the left inferior frontal cortex, premotor cortex, and anterior insula, bilaterally in the parietal lobes and superior cerebellum, and in the right inferior cerebellum. This network shares substrates with overt speech and may represent an inner speech pathway that increases activity with greater working memory demands. Additionally, an inverse correlation was observed between manipulation-related brain activity (on correct trials) and test accuracy in the left premotor cortex, anterior insula, and bilateral superior cerebellum. This inverse relationship may represent intensification of inner speech as one struggles to maintain performance levels.     

Sensorimotor foundations of speech perception in infancy

The perceptual system for speech is highly organized from early infancy. This organization bootstraps young human learners’ ability to acquire their native speech and language from speech input. Here, we review behavioral and neuroimaging evidence that perceptual systems beyond the auditory modality are also specialized for speech in infancy, and that motor and sensorimotor systems can influence speech perception even in infants too young to produce speech-like vocalizations. These investigations complement existing literature on infant vocal development and on the interplay between speech perception and production systems in adults. We conclude that a multimodal speech and language network is present before speech-like vocalizations emerge.     

数字加工的认知神经基础

数学作为人类最重要的发明,越来越引起认知神经科学家的重视与关注,究竟什么才是人类数学知识的脑基础？脑成像的研究已经证实了一个参与数学运算加工的神经网络,包括顶叶皮质、侧前额叶皮质、内前额叶皮质、和小脑。实验证明：人脑对于数字具有一种模拟表达,类似于将数量在脑内部作为一种内心的数字线上的点来操作。神经心理学的研究证实数字加工的这种数量表达分布于两半球,其优势区位于下顶叶皮质区。     

Motor functions of the Broca's region

Broca's region in the dominant cerebral hemisphere is known to mediate the production of language but also contributes to comprehension. This region evolved only in humans and is constituted of Brodmann's areas 44 and 45 in the inferior frontal gyrus. There is, however, evidence that Broca's region overlaps, at least in part, with the ventral premotor cortex. We summarize the evidence that the motor related part of Broca's area is localized in the opercular portion of the inferior frontal cortex, mainly in area 44 of Brodmann. According to our own data, there seems to be a homology between Brodmann area 44 in humans and the monkey area F5. The non-language related motor functions of Broca's region comprise complex hand movements, associative sensorimotor learning and sensorimotor integration. Brodmann's area 44 is also a part of a specialized parieto-premotor network and interacts significantly with the neighboring premotor areas.     

Subjective experience is probably not limited to humans: the evidence from neurobiology and behavior

In humans, conscious perception and cognition depends upon the thalamocortical (T-C) complex, which supports perception, explicit cognition, memory, language, planning, and strategic control. When parts of the T-C system are damaged or stimulated, corresponding effects are found on conscious contents and state, as assessed by reliable reports. In contrast, large regions like cerebellum and basal ganglia can be damaged without affecting conscious cognition directly. Functional brain recordings also show robust activity differences in cortex between experimentally matched conscious and unconscious events. This basic anatomy and physiology is highly conserved in mammals and perhaps ancestral reptiles. While language is absent in other species, homologies in perception, memory, and motor cortex suggest that consciousness of one kind or another may be biologically fundamental and phylogenetically ancient. In humans we infer subjective experiences from behavioral and brain evidence. This evidence is quite similar in other mammals and perhaps some non-mammalian species. On the weight of the biological evidence, therefore, subjectivity may be conserved in species with human-like brains and behavior.     

The functional neuroanatomy of prelexical processing in speech perception

In this paper we attempt to relate the prelexical processing of speech, with particular emphasis on functional neuroimaging studies, to the study of auditory perceptual systems by disciplines in the speech and hearing sciences. The elaboration of the sound-to-meaning pathways in the human brain enables their integration into models of the human language system and the definition of potential auditory processing differences between the two cerebral hemispheres. Further, it facilitates comparison with recent developments in the study of the anatomy of non-human primate auditory cortex, which has very precisely revealed architectonically distinct regions, connectivity, and functional specialization.     

Neuroanatomical correlates of handedness for tool use in chimpanzees (Pan troglodytes): implication for theories on the evolution of language

It has been hypothesized that cognitive mechanisms underlying lateralized complex motor actions associated with tool use in chimpanzees may have set the stage for the evolution of left-hemisphere specialization for language and speech in humans. Here we report evidence that asymmetries in the homologues to Broca's and Wernicke's areas are associated with handedness for tool use in chimpanzees. These results suggest that the neural substrates of tool use may have served as a preadaptation for the evolution of language and speech in modern humans.     

The influence of syllable onset complexity and syllable frequency on speech motor control

Functional imaging studies have delineated a "minimal network for overt speech production", encompassing mesiofrontal structures (supplementary motor area, anterior cingulate gyrus), bilateral pre- and postcentral convolutions, extending rostrally into posterior parts of the inferior frontal gyrus (IFG) of the language-dominant hemisphere, left anterior insula as well as bilateral components of the basal ganglia, the cerebellum, and the thalamus. In order to further elucidate the specific contribution of these cerebral regions to speech motor planning, subjects were asked to read aloud visually presented bisyllabic pseudowords during functional magnetic resonance imaging (fMRI). The test stimuli systematically varied in onset complexity (CCV versus CV) and frequency of occurrence (high-frequency, HF versus low-frequency, LF) of the initial syllable. A cognitive subtraction approach revealed a significant main effect of syllable onset complexity (CCV versus CV) at the level of left posterior IFG, left anterior insula, and both cerebellar hemispheres. Conceivably, these areas closely cooperate in the sequencing of subsyllabic aspects of the sound structure of verbal utterances. A significant main effect of syllable frequency (LF versus HF), by contrast, did not emerge. However, calculation of the time series of hemodynamic activation within the various cerebral structures engaged in speech motor control revealed this factor to enhance functional connectivity between Broca's area and ipsilateral anterior insula.     

Neural correlates of phonological processing in speech sound disorder: a functional magnetic resonance imaging study

Speech sound disorders (SSD) are the largest group of communication disorders observed in children. One explanation for these disorders is that children with SSD fail to form stable phonological representations when acquiring the speech sound system of their language due to poor phonological memory (PM). The goal of this study was to examine PM in individuals with histories of SSD employing functional MR imaging (fMRI). Participants were six right-handed adolescents with a history of early childhood SSD and seven right-handed matched controls with no history of speech and language disorders. We performed an fMRI study using an overt non-word repetition (NWR). Right lateralized hypoactivation in the inferior frontal gyrus and middle temporal gyrus was observed. The former suggests a deficit in the phonological processing loop supporting PM, while the later may indicate a deficit in speech perception. Both are cognitive processes involved in speech production. Bilateral hyperactivation observed in the pre and supplementary motor cortex, inferior parietal, supramarginal gyrus and cerebellum raised the possibility of compensatory increases in cognitive effort or reliance on the other components of the articulatory rehearsal network and phonologic store. These findings may be interpreted to support the hypothesis that individuals with SSD may have a deficit in PM and to suggest the involvement of compensatory mechanisms to counteract dysfunction of the normal network.