Renewal of the Neurophysiology of Language: Functional Neuroimaging

Abstract

Functional neuroimaging methods have reached maturity. It is now possible to start to build the foundations of a physiology of language. The remarkable number of neuroimaging studies performed so far illustrates the potential of this approach, which complements the classical knowledge accumulated on aphasia. Here we attempt to characterize the impact of the functional neuroimaging revolution on our understanding of language. Although today considered as neuroimaging techniques, we refer less to electroencephalography and magnetoencephalography studies than to positron emission tomography and functional magnetic resonance imaging studies, which deal more directly with the question of localization and functional neuroanatomy. This review is structured in three parts. 1) Because of their rapid evolution, we address technical and methodological issues to provide an overview of current procedures and sketch out future perspectives. 2) We review a set of significant results acquired in normal adults (the core of functional imaging studies) to provide an overview of language mechanisms in the “standard” brain. Single-word processing is considered in relation to input modalities (visual and auditory input), output modalities (speech and written output), and the involvement of “central” semantic processes before sentence processing and nonstandard language (illiteracy, multilingualism, and sensory deficits) are addressed. 3) We address the influence of plasticity on physiological functions in relation to its main contexts of appearance, i.e., development and brain lesions, to show how functional imaging can allow fine-grained approaches to adaptation, the fundamental property of the brain. In closing, we consider future developments for language research using functional imaging.

Cortical activity during speech and non-speech oromotor tasks: A magnetoencephalography (MEG) study

“…We found no clear left hemisphere dominance per se for the speech task. This is consistent with more recent speculations within the literature that left greater than right asymmetries may be due to stimulation paradigms and task parameters [9]. We did observe an almost exclusive activation of right pre-central gyrus.…”

Localization of Broca's area using verb generation tasks in the MEG: Validation against fMRI

“…Receptive language is located in Wernicke's area [4] at the left temporo-parietal junction. These areas have complex, reciprocal connections between primary sensory, secondary sensory, and association areas [5]. Notwithstanding the limitations inherent in a simplified model, the application of this model to the study of language is of practical use.…”

Functional MRI evidence for language plasticity in adult epileptic patients: Preliminary results

“…With respect to healthy subjects, the patients with chronic temporal epileptogenic show reorganization of temporal language networks (Hertz-Pannier et al 2002;Breier et al 2005;Pataraia et al 2004Pataraia et al , 2005. As the left temporal lobe is involved in language (Billingsley et al 2001;Seghier et al 2004;Gitelman et al 2005), an atypical representation (bilateral hemispheric representation or right hemispheric predominance) of the subjacent cerebral regions, could occur (Adcock et al 2003;Demonet et al 2005). Overall, when the epileptogenic zone is located within the predominant hemisphere for language, two types of cerebral reorganization have been generally described: (a) intra-hemispheric, ie, the nonaffected cerebral regions from the hemisphere where the epileptogenic zone is located in, take over language functions, for instance, the language function of the temporal region could "shift" within the frontal region of the same hemisphere, when the epileptogenic zone is situated in the temporal lobe (Bell et al 2002;Brazdil et al 2003;Pataraia et al 2004Pataraia et al , 2005Kadis et al 2007) and (b) inter-hemispheric, ie, the homologues cerebral regions situated within the nonpredominant hemisphere for language become involved in language (Hertz-Pannier et al 2002;Pataraia et al 2004Pataraia et al , 2005Breier et al 2005; Cousin et al Thivard et al 2005;Helmstaedter et al 2006).…”

“…Overall, when the epileptogenic zone is located within the predominant hemisphere for language, two types of cerebral reorganization have been generally described: (a) intra-hemispheric, ie, the nonaffected cerebral regions from the hemisphere where the epileptogenic zone is located in, take over language functions, for instance, the language function of the temporal region could "shift" within the frontal region of the same hemisphere, when the epileptogenic zone is situated in the temporal lobe (Bell et al 2002;Brazdil et al 2003;Pataraia et al 2004Pataraia et al , 2005Kadis et al 2007) and (b) inter-hemispheric, ie, the homologues cerebral regions situated within the nonpredominant hemisphere for language become involved in language (Hertz-Pannier et al 2002;Pataraia et al 2004Pataraia et al , 2005Breier et al 2005; Cousin et al Thivard et al 2005;Helmstaedter et al 2006). The type of reorganization may depend on many factors such as the age of seizures onset (Hertz-Pannier et al 2002;Liegeois et al 2004;Berl et al 2005;Demonet et al 2005;Goldmann and Golby 2005;Thivard et al 2005), the considered language region, temporo-parietal or frontal (Kurthen et al 1992;Hertz-Pannier et al 2002;Liegeois et al 2004;Thivard et al 2005) or the associated hippocampal sclerosis (Knecht 2004;Janszky et al 2006;Weber et al 2006).…”