Language is the ability to acquire and use complex systems of communication, particularly the human ability to do so, and a language is any specific example of such a system. The scientific study of language is called linguistics.
see Language area.
see Language dysfunction.
see Language mapping.
The cortical localization of language varies in different individuals, particularly in patients with intracranial lesions where the atypical distribution of the language cortex is particularly common 1).
The ability to locate the language cortex is the key towards surgery in the dominant hemisphere, particularly surgery of lesions close to the language area. How best to perform resection of lesions in the language area of the brain without inducing a postoperative language disorder, thus protecting the patient's quality of life, has become an issue of particular concern in neurosurgery currently 2) 3) 4) 5).
Classic models of language organization posited that separate motor and sensory language foci existed in the inferior frontal gyrus (Broca's area) and superior temporal gyrus (Wernicke's area), respectively, and that connections between these sites (arcuate fasciculus) allowed for auditory-motor interaction.
These theories have predominated for more than a century, but advances in neuroimaging and stimulation mapping have provided a more detailed description of the functional neuroanatomy of language. New insights have shaped modern network-based models of speech processing composed of parallel and interconnected streams involving both cortical and subcortical areas. Recent models emphasize processing in “dorsal” and “ventral” pathways, mediating phonological and semantic processing, respectively. Phonological processing occurs along a dorsal pathway, from the posterosuperior temporal to the inferior frontal cortices. On the other hand, semantic information is carried in a ventral pathway that runs from the temporal pole to the basal occipitotemporal cortex, with anterior connections.
Functional MRI has poor positive predictive value in determining critical language sites and should only be used as an adjunct for preoperative planning.
In tracing the historical advancements in our understanding of speech processing, Chang et al. hope to not only provide practicing neurosurgeons with additional information that will aid in surgical planning and prevent postoperative morbidity, but also underscore the fact that neurosurgeons are in a unique position to further advance our understanding of the anatomy and functional organization of language 6).
Human language organization models and language time course patterns are still predominantly derived from meta-analyses of numerous single publications, which only investigated scattered cortical regions. Moreover, there is not much literature available on the exact impact of repetitive navigated transcranial magnetic stimulation (rTMS) onset times on object naming. We, therefore, used a virtual lesion-based approach by mapping various cortical areas with rTMS to investigate the time course of object naming, and to specifically provide data on the pattern of rTMS language mapping results depending on different stimulation onset times. Ten healthy, right-handed subjects were enrolled, and rTMS in combination with an object-naming task was performed with different stimulation onset times (0 ms, 100 ms, 200 ms, 300 ms, 400 ms, and 500 ms). Subsequent to language mapping, all naming errors detected were systematically classified with respect to previous literature. The majority of errors was elicited within the opercular inferior frontal gyrus (opIFG) and ventral precentral gyrus (vPrG), and the spatial distribution of naming errors changed according to the time point of naming disruption by varying onset times. For instance, immediate rTMS onset led to a widespread cortical distribution of no responses, whereas performance and hesitation errors increased with higher stimulation onset times 7).