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Origin and function of hemispheric asymmetry for language: insights from neuroscience, animal models and clinical practice.

Wednesday, October 25, 8:00 - 10:00 am CEST, Auditorium

Organizer: Benjamin Morillon^1,2; ¹Aix Marseille Université, ²Inserm
Presenters: Adrien Meguerditchian, Yannick Becker, Pascal Belin, Benjamin Morillon, Christian Kell, Agnès Trébuchon

Our interdisciplinary symposium aims to shed light on the origin and function of hemispheric asymmetry for language through fundamental and clinical research, language perception and production research, as well as comparative evolutionary approaches across primates. It offers the latest perspectives on this historic question in cognitive neuroscience, with the comparison of complementary and even incompatible points of view. In particular, the sensory or motor origin of brain asymmetry will be debated, together with the presence or absence of lateralization of specific cognitive processes. The symposium is suitable for students and faculty interested in cognitive neuroscience, linguistics, and communication disorders. Attendees will benefit from gaining knowledge on the latest theories and empirical findings that describe the complex relationship between brain asymmetry and language processing. Overall, this symposium offers a unique opportunity to explore the cutting-edge research on hemispheric specialization in the brain and its implications for language and communication.

Presentations

Gesture and brain asymmetries in baboons: A model of hemispheric specialization for language?

Adrien Meguerditchian¹; ¹Aix Marseille Université, ²CNRS

Language is a unique communicative system involving hemispheric lateralization of the brain. Such a lateralization is visible at the structural level, even at birth, in key cortical language areas, such as the perisylvian Planum Temporale, its main connecting fiber track with Broca’s area - the arcuate fasciculus and the STS. To discuss the question of language origins, the studies of the communicative gestural system of our primate cousins, including our own research in baboons, have showed similar key intentional and referential properties of language as well as some similar underlying structural hemispheric specialization. In this talk, I will present behavioral and in vivo MRI brain imaging studies in baboons Papio anubis reporting not only human-like structural brain asymmetries of some language-homolog regions in both 93 adults and 30 newborns, but also its correlates with the communicative gestures lateralization.

New insights about the arcuate fascicle in chimpanzees: lateralization and temporal projections.

Yannick Becker¹; ¹Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig

Many authors have argued that the difference between the linguistic abilities of humans and non-human primates may lie in the differences in neural connectivity between the species. In the human brain, the main connection for language processing is the arcuate fascicle (AF). It arches dorsally around the sylvian fissure and connects frontal and temporal language areas. Although the architecture of language brain regions is highly conserved among primates, it is possible that the AF has undergone a major morphological transformation that accounts for our specificity in language processing. Indeed, only humans are described as having a long and left-lateralized AF terminating in the middle temporal gyrus. Here, using developmental and high-resolution data from the Evolution of Brain Connectivity Project, I will revisit and update the crucial questions about the evolution of the language fiber tract that makes us human. Possible behavioral correlates will be discussed.

Hemispheric lateralization of the temporal voice areas.

Pascal Belin¹; ¹Aix Marseille Université, ²CNRS

The temporal voice areas (TVAs) of primate secondary auditory cortex are important nodes in the cerebral processing of information contained in conspecific vocalizations. While being highly variable in anatomical location between individuals, an analysis of several 100s participants did not reveal any significant asymmetry between the left and right TVAs. The TVAs are thought to reflect an essentially bilateral and symmetric initial stage of template matching, or ‘structural encoding’ restricted to vocal sounds, after which the main types of voice information (speech, identity, affect) are processed in more strongly lateralized functional pathways.

Auditory hemispheric asymmetry as a specialization for actions and objects.

Benjamin Morillon¹; ¹Aix Marseille Université, ²Inserm

What is the function of auditory hemispheric asymmetry? We propose that the identification of sound sources relies on two complementary perceptually relevant acoustic invariants — actions and objects — that are processed asymmetrically and sufficient to model and categorize any sound. We observed that environmental sounds are an independent combination of purely temporal and spectral acoustic modulations. Behaviorally, discrimination of actions relies on temporal modulations, while discrimination of objects relies on spectral modulations. Functional magnetic resonance imaging data showed that actions and objects are respectively decoded in left and right hemispheres, in bilateral superior temporal and left inferior frontal regions. This asymmetry reflects a generic differential processing — through differential neural sensitivity to temporal and spectral modulations present in all environmental sounds — that supports the efficient categorization of actions and objects. These results provide an ecologically valid framework of the functional role of auditory brain asymmetry.

A perceptual control framework explaining contributions of the dominant and non-dominant cerebral hemisphere to speech production.

Christian Kell¹; ¹Goethe University, ²Department of Neurology of Frankfurt

Hemispheric asymmetries are particularly pronounced for production compared to perception tasks. The best-established speech production model that links computational processes to brain regions, DIVA, proposes a left-hemispheric feedforward and a right-lateralized auditory feedback controller (Tourville and Guenther, 2011). We investigated whether the observed right-lateralization for auditory feedback control arises from a specialization of the right hemisphere for spectral processing (Albouy et al., 2020) or from a right-lateralization for auditory feedback control in general (Tourville and Guenther, 2011). Indeed, both cerebral hemispheres contribute to speech production with the left favouring temporal and the right favouring spectral auditory feedback control (Floegel, Fuchs and Kell, 2020). However, parallel feedback controllers are difficult to reconcile with the idea of unified motor commands controlling a plant that has no intrinsic time, as conceived in DIVA. We therefore propose a dynamic hierarchical perceptual control scheme that incorporates these novel insights (Floegel et al., in press).

Hemispheric asymmetry of language network: what does it mean in epilepsy surgery?

Agnès Trébuchon¹; ¹Aix Marseille Université, ²Inserm, ³APHM, La Timone hospital

The challenge in epilepsy surgery is to cure patients without causing an additional neurological deficit, which typically requiring determination of language lateralization between hemispheres. The surgical disruption of any component, be it core or peripheral to language functions, have distinct consequences for language processing and performance. Hence, a clinical discussion of lateralization must be framed in terms of specific functional sub-units such as lexical selection, or anatomo-functional subdivisions such as the dorsal pathway of processing. In addition, the lesion underlying drug resistant epilepsy may result in a functional organization different from healthy individuals. As such, neuropsychological data, handedness, intracerebral recordings, electrical cortical stimulation, and electro-video analyses of seizures are used in clinical practices to determine language systems. We highlight why no single modality alone is adequate to identify cortical language systems.