Abstract
Early biological concepts of language were predominantly corticocentric, but over the last decades biolinguistic research, equipped with new technical possibilities, has drastically changed this view. To date, connectionist models, conceiving linguistic skills as corticobasal network activities, dominate our understanding of the neural basis of language. However, beyond the notion of an involvement of the thalamus and, in most cases also, the basal ganglia (BG) in linguistic operations, specific functions of the respective depth structures mostly remain rather controversial. In this review, some of these issues shall be discussed, particularly the functional configuration of basal network components and the language specificity of subcortical supporting activity. Arguments will be provided for a primarily cortico-thalamic language network. In this view, the thalamus does not engage in proper linguistic operations, but rather acts as a central monitor for language-specific cortical activities, supported by the BG in both perceptual and productive language execution.
Highlights
Over the last decades, functional imaging and neurophysiological techniques have allowed for an increasingly detailed allocation of mental functions to cortical structures and processes, whereas subcortical functions in cognitive processing still remain somewhat elusive
Since language deficits have frequently been described following other subcortical damage, e.g., basal ganglia (BG) lesions (Damasio et al, 1982; Perani et al, 1987; Weiller et al, 1990; Hillis et al, 2001; Russmann et al, 2003; Hillis et al, 2004; Han et al, 2005; Choi et al, 2007; Pellizzaro Venti et al, 2012), there have been attempts to differentiate the aphasia types occurring in thalamic vs. striato-capsular and paraventricular white matter infarction (Kuljic-Obradovic, 2003)
Many patients had preserved non-propositional speech, i.e., language repetition remained relatively intact. Another striking feature was the preservation of the speech syntax in this cohort. From this it was concluded that a ‘transcortical aphasia’ type was more likely to occur in left thalamic damage than in other brain lesions apart from that of the dominant supplementary motor region (SMR) (Jonas, 1981, 1982)
Summary
Functional imaging and neurophysiological techniques have allowed for an increasingly detailed allocation of mental functions to cortical structures and processes, whereas subcortical functions in cognitive processing still remain somewhat elusive. This and their widespread connections appear to enable thalamic nuclei to monitor and adapt the network constellations needed for ongoing behaviors, a function rather emerging from an intricate two-way exchange with cortical information than from processing between hierarchically organized brain structures.
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