Bilingualism

Social Cognitive Neuroscience, Cognitive Neuroscience, Clinical Brain Mapping

J. Abutalebi, D. Perani, in Brain Mapping, 2015

Introduction

The human brain not only has evolved to accommodate a single language but also is, in fact, suited to acquire more than one language, such as the case of bilingual and multilingual individuals. As globalization advances, more people become bilingual or multilingual thus establishing bilingualism as the standard rather than the exception (Grosjean & Li, 2013). A bilingual individual may achieve different levels of proficiency in the two languages, using both languages in different contexts, by learning a new language following educational requirements, immigration, or alternative circumstances. By this definition, a bilingual individual is not only necessarily someone who has acquired both languages from birth, or early in life, but also that one who learns a second language (L2) later in life. The different contexts and circumstances of L2 acquisition have important effects upon the cerebral organization of multiple languages. Moreover, having acquired more than one language, the bilingual or multilingual speaker may eventually encounter potential conflicts between said languages, such as how to speak in one language while avoiding potential intrusions from the other.
As a broad definition, the concept of neural representation of bilingualism refers to functional and structural neuroimaging evidence that provided the cerebral organization of two (or more) languages. These studies focus on not only how two or more languages are anatomically represented in the human brain, according to crucial variables such as proficiency, age of acquisition (AOA), and exposure, but also, ultimately, how individuals acquire, process, and eventually may later lose such languages.
From a historical viewpoint, the landmark study of Pitres (1895) marked the initiation of this field and has enticed the interest of researchers for more than a century. Pitres in 1896 described cases of selective loss and recovery of a given language in bilingual aphasics, thus giving rise to vivid discussions about different potential neural locations for languages. Indeed, prior to the advent of functional neuroimaging, it was widely believed that bilingual language representation was assigned to different brain areas or even different hemispheres (Albert & Obler, 1978). This hypothesis was essentially based on the common observation of bilingual aphasics who recover only one language after stroke, while the other is lost; this led researchers to believe that the brain regions responsible for one language was damaged though the others remained intact. However, functional neuroimaging studies have so far contradicted this assumption (see, for review, Abutalebi, 2008; Indefrey, 2006; Perani & Abutalebi, 2005). Today, it is well established that bilinguals use the same neural substrate, thus identical brain structures for both languages. The neural networks can vary according to variables that influence neural plasticity, among those, the exposure or amount of use to a given language.
In this article, we will provide a brief overview of how two or more languages are organized in the human brain and what mediates their processes.