The auditory and association cortex and language evaluation methods

Abstract

This chapter presents a summary of current notions regarding cortical specialization for language and a description of the methods employed for the assessment of that specialization. We distinguish between the "canonical" model of language specialization as it evolved from the early observations of Broca and Wernicke, implicating the inferior frontal gyrus and the posterior temporal cortex of the speech dominant hemisphere (usually the left) and its modern variants that are based on both detailed studies of lesion-symptom correlations and on the results of functional brain mapping methods. The latter fall into two categories. The first includes the invasive ones, namely the Wada procedure for assessing hemispheric dominance for speech and cortical stimulation mapping (whether intraoperative or extraoperative) for identifying cortical nodes or "hubs" of the neuronal network for language. The second category includes the noninvasive methods of functional magnetic resonance imaging, magnetoencephalography, and transcranial magnetic stimulation used for both assessment of hemispheric dominance for language and for localization of the cortical nodes of the language network. The advantages and the shortcomings of all methods are juxtaposed to facilitate selection of particular methods of assessment of the locus of the language network in particular cases.

Keywords: Cortical stimulation mapping; Functional magnetic resonance imaging (fMRI); Language; Laterality; Magnetoencephalography (MEG); Transcranial magnetic stimulation (TMS); Wada procedure.