The specialized structure of human language cortex: pyramidal cell size asymmetries within auditory and language-associated regions of the temporal lobes

Functional lateralization of language within the cerebral cortex has long driven the search for structural asymmetries that might underlie language asymmetries. Most examinations of structural asymmetry have focused upon the gross size and shape of cortical regions in and around language areas. In the last 20 years several labs have begun to document microanatomical asymmetries in the structure of language-associated cortical regions. Such microanatomic results provide useful constraints and clues to our understanding of the biological bases of language specialization in the cortex. In a previous study we documented asymmetries in the size of a specific class of pyramidal cells in the superficial cortical layers. The present work uses a nonspecific stain for cell bodies to demonstrate the presence of an asymmetry in layer III pyramidal cell sizes within auditory, secondary auditory and language-associated regions of the temporal lobes. Specifically, the left hemisphere contains a greater number of the largest pyramidal cells, those that are thought to be the origin of long-range cortico-cortical connections. These results are discussed in the context of cortical columns and how such an asymmetry might alter cortical processing. These findings, in conjunction with other asymmetries in cortical organization that have been documented within several labs, clearly demonstrate that the columnar and connective structure of auditory and language cortex in the left hemisphere is distinct from homotopic regions in the contralateral hemisphere.

Evolutionary biology of language

Language is the most important evolutionary invention of the last few million years. It was an adaptation that helped our species to exchange information, make plans, express new ideas and totally change the appearance of the planet. How human language evolved from animal communication is one of the most challenging questions for evolutionary biology The aim of this paper is to outline the major principles that guided language evolution in terms of mathematical models of evolutionary dynamics and game theory. I will discuss how natural selection can lead to the emergence of arbitrary signs, the formation of words and syntactic communication.

The evolution of language

The emergence of language was a defining moment in the evolution of modern humans. It was an innovation that changed radically the character of human society. Here, we provide an approach to language evolution based on evolutionary game theory. We explore the ways in which protolanguages can evolve in a nonlinguistic society and how specific signals can become associated with specific objects. We assume that early in the evolution of language, errors in signaling and perception would be common. We model the probability of misunderstanding a signal and show that this limits the number of objects that can be described by a protolanguage. This "error limit" is not overcome by employing more sounds but by combining a small set of more easily distinguishable sounds into words. The process of "word formation" enables a language to encode an essentially unlimited number of objects. Next, we analyze how words can be combined into sentences and specify the conditions for the evolution of very simple grammatical rules. We argue that grammar originated as a simplified rule system that evolved by natural selection to reduce mistakes in communication. Our theory provides a systematic approach for thinking about the origin and evolution of human language.