Can a Morphological Feature of Dendritic Structure be Linked to Language Acquisition?

Abstract

Eric Lennenberg (1967) popularized the notion of a critical period for language acquisition, an ideal developmental time window, from approximately age two to puberty, beyond which achieving native-speaker like competence is greatly diminished. The critical period hypothesis (CPH) has been and continues to be a much discussed and controversial topic, particularly in the context of second language acquisition (for a review see Birdsong, in press). My contribution to this discussion is very limited and focused on a specific issue—that is, can an enhanced, developmentally-based feature, empirically documented within a neuron’s dendritic arborization, play a role in language acquisition? A reasonable expectation is that in a normal postnatal environment, a functional enrichment of neuronal circuitry interconnecting brain regions engaged in speech and language processing should parallel and underlie the emergence of a natural language in a child. From initial vocalic-like cries and squeals, to canonical and variegated babbling, to first words, to two word utterances, and culminating in the production of sentences, one would expect a concomitant maturation of the complex neural infrastructure mediating this genetically and experientially driven, but poorly understood, cognitive achievement. What may be unreasonable, however, is an expectation of linking neuroanatomical features of micro-level structure to cognitive function. Fifty years ago, Lennenberg cautioned against making such claims: