Andre Guillemin

Bio: Andre Guillemin is an academic researcher from National Institutes of Health. The author has contributed to research in topics: Sign language & Language production. The author has an hindex of 4, co-authored 4 publications receiving 431 citations.

The neural organization of discourse: an H2 15O-PET study of narrative production in English and American sign language.

Abstract: In order to identify brain regions that play an essential role in the production of discourse, H2 15O-PET scans were acquired during spontaneous generation of autobiographical narratives in English and in American Sign Language in hearing subjects who were native users of both. We compared languages that differ maximally in their mode of expression yet share the same core linguistic properties in order to differentiate the stages of discourse production: differences between the languages should reflect later, modality-dependent stages of phonological encoding and articulation; congruencies are more likely to reveal the anatomy of earlier modality-independent stages of conceptualization and lexical access. Common activations were detected in a widespread array of regions; left hemisphere language areas classically related to speech were also robustly activated during sign production, but the common neural architecture extended beyond the classical language areas and included extrasylvian regions in both right and left hemispheres. Furthermore, posterior perisylvian and basal temporal regions appear to play an integral role in spontaneous self-generated formulation and production of language, even in the absence of exteroceptive stimuli. Results additionally indicate that anterior and posterior areas may play distinct roles in early and late stages of language production, and suggest a novel model for lateralization of cerebral activity during the generation of discourse: progression from the early stages of lexical access to later stages of articulatory-motor encoding may constitute a progression from bilateral to left-lateralized activation. This pattern is not predicted by the standard Wernicke-Geschwind model, and may become apparent when language is produced in an ecologically valid context.

Language Lateralization in a Bimanual Language

Abstract: Unlike spoken languages, sign languages of the deaf make use of two primary articulators, the right and left hands, to produce signs. This situation has no obvious parallel in spoken languages, in which speech articulation is carried out by symmetrical unitary midline vocal structures. This arrangement affords a unique opportunity to examine the robustness of linguistic systems that underlie language production in the face of contrasting articulatory demands and to chart the differential effects of handedness for highly skilled movements. Positron emission tomography (PET) technique was used to examine brain activation in 16 deaf users of American Sign Language (ASL) while subjects generated verb signs independently with their right dominant and left nondominant hands (compared to the repetition of noun signs). Nearly identical patterns of left inferior frontal and right cerebellum activity were observed. This pattern of activation during signing is consistent with patterns that have been reported for spoken languages including evidence for specializations of inferior frontal regions related to lexical-semantic processing, search and retrieval, and phonological encoding. These results indicate that lexical-semantic processing in production relies upon left-hemisphere regions regardless of the modality in which a language is realized, and that this left-hemisphere activation is stable, even in the face of conflicting articulatory demands. In addition, these data provide evidence for the role of the right posterolateral cerebellum in linguistic-cognitive processing and evidence of a left ventral fusiform contribution to sign language processing.

Neural systems for sign language production: Mechanisms supporting lexical selection, phonological encoding, and articulation

Abstract: Overt production of ASL signs was evaluated using H(2)(15)O PET to differentiate brain systems that support sign language production at the lexical-selection and phonological-articulatory levels. Subjects were 16 right-handed, congenitally deaf native ASL signers (10 women, six men; age 20 to 29 years). Scans were performed while subjects (1) passively viewed ASL nouns, (2) repeated nouns, (3) generated verbs in response to these nouns, (4) passively viewed videotaped segments depicting transitive actions, and (5) generated a verb to describe these actions. Conjunctions between the two verb-generation tasks revealed left-lateralized activation of perisylvian, frontal, and subcortical regions commonly observed in spoken language generation tasks and implicated in processes of semantic feature binding and lexical selection. Analysis of noun repetition minus viewing condition revealed activation of distinct systems supporting phonological encoding and articulation, including bilateral activation of sensorimotor areas and association cortices in the temporal, parietal, and occipital lobes. In addition, lexical-selection and articulatory processes were associated with activation of different corticostriatal-thalamocortical circuits: articulation with activation of the motor, and lexical-selection with activation of the prefrontal circuits, respectively. The results collectively provide insight into dissociable neural systems underlying these psycholinguistic functions. In addition, activation of regions that are typically associated with the auditory system during sign production suggests that these regions may support modality-independent linguistic processes, or may indicate cross-modal plasticity within the deaf brain.

From monkey-like action recognition to human language: an evolutionary framework for neurolinguistics.

Abstract: The article analyzes the neural and functional grounding of language skills as well as their emergence in hominid evolution, hypothesizing stages leading from abilities known to exist in monkeys and apes and presumed to exist in our hominid ancestors right through to modern spoken and signed languages. The starting point is the observation that both premotor area F5 in monkeys and Broca's area in humans contain a "mirror system" active for both execution and observation of manual actions, and that F5 and Broca's area are homologous brain regions. This grounded the mirror system hypothesis of Rizzolatti and Arbib (1998) which offers the mirror system for grasping as a key neural "missing link" between the abilities of our nonhuman ancestors of 20 million years ago and modern human language, with manual gestures rather than a system for vocal communication providing the initial seed for this evolutionary process. The present article, however, goes "beyond the mirror" to offer hypotheses on evolutionary changes within and outside the mirror sys- tems which may have occurred to equip Homo sapiens with a language-ready brain. Crucial to the early stages of this progression is the mirror system for grasping and its extension to permit imitation. Imitation is seen as evolving via a so-called simple system such as that found in chimpanzees (which allows imitation of complex "object-oriented" sequences but only as the result of extensive practice) to a so-called complex system found in humans (which allows rapid imitation even of complex sequences, under appropriate conditions) which supports pantomime. This is hypothesized to have provided the substrate for the development of protosign, a combinatorially open reper- toire of manual gestures, which then provides the scaffolding for the emergence of protospeech (which thus owes little to nonhuman vo- calizations), with protosign and protospeech then developing in an expanding spiral. It is argued that these stages involve biological evo- lution of both brain and body. By contrast, it is argued that the progression from protosign and protospeech to languages with full-blown syntax and compositional semantics was a historical phenomenon in the development of Homo sapiens, involving few if any further bio- logical changes.

DTI Tractography of the Human Brain's Language Pathways

Abstract: Diffusion Tensor Imaging (DTI) tractography has been used to detect leftward asymmetries in the arcuate fasciculus, a pathway that links temporal and inferior frontal language cortices. In this study, we more specifically define this asymmetry with respect to both anatomy and function. Twenty right-handed male subjects were scanned with DTI, and the arcuate fasciculus was reconstructed using deterministic tractography. The arcuate was divided into 2 segments with different hypothesized functions, one terminating in the posterior superior temporal gyrus (STG) and another terminating in the middle temporal gyrus (MTG). Tractography results were compared with peak activation coordinates from prior functional neuroimaging studies of phonology, lexical-semantic processing, and prosodic processing to assign putative functions to these pathways. STG terminations were strongly left lateralized and overlapped with phonological activations in the left but not the right hemisphere, suggesting that only the left hemisphere phonological cortex is directly connected with the frontal lobe via the arcuate fasciculus. MTG terminations were also strongly left lateralized, overlapping with left lateralized lexical-semantic activations. Smaller right hemisphere MTG terminations overlapped with right lateralized prosodic activations. We combine our findings with a recent model of brain language processing to explain 6 aphasia syndromes.