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date: 08 March 2021

Abstract and Keywords

This article gives an overview on the various brain structures, other than neocortex, contributing to speech and language. The regions of the avian brain which are considered functionally homologous to human neocortex, are nuclear, as opposed to cortical, in their cellular arrangements. The functional significance of nuclear versus cortical neuronal arrangements remains unknown. The intelligence is best measured by ratios that explicitly and/or implicitly discount other neural areas. The most extreme such measure is Dunbar's neocortical ratio that is the ratio of the size of the neocortex to the size of the entire remainder of the brain. The ratio, which is based on the explicit assumption that the neocortex is the primary seat of intelligence, also rests on the implicit assumption that enlargement of non-neocortical brain structures lowers intelligence. The nuclei and basal ganglia contain neurons that are arranged in a non-layered fashion. Such structures may also lie entirely within the brain, and thus have no visible representation on the outer brain surface. The cerebellar lesions can be associated with a much wider range of cognitive and sensory defects, including defects in working memory, procedural learning, syntax, word order, word choice, and autism. The deficits in both the basal ganglia and the cerebellum accompany the orofacial dyspraxia that results from FOXP2 mutations.

Keywords: neocortex, FOXP2 mutations, Dunbar's neocortical ratio, intelligence, neural areas

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