Vol. 366, Issue 6461, pp. 13
Languages—exquisitely structured, complex, and diverse—are a distinctively human gift, at the very heart of what it means to be human. As such, language makes for both a particularly important and difficult topic in neuroscience. A dominant early approach to the study of language was to treat it as a separate module or organ within the brain. However, much modern empirical work has demonstrated that language is integrated with, and in constant interplay with, an incredibly broad range of neural processes.
Unlike other areas of neuroscience investigation (e.g., vision, motor action) that have relied heavily on invasive techniques with animal models, the study of language lacks any such model. Furthermore, in language, the relationship between the form of a signal and its meaning is largely arbitrary. For example, the sound of “blue” will likely have no relationship to the properties of light we experience as blue nor to the visual written form “blue,” will sound different across languages, and have no sound at all in signed languages. No equivalent of “blue” will even exist in many languages that might make fewer or more or different color distinctions. With respect to language, the meaning of a signal cannot be predicted from the physical properties of the signal available to the senses. Rather, the relationship is set by convention.
At the same time, language is a powerful engine of human intellect and creativity, allowing for endless recombination of words to generate an infinite number of new structures and ideas out of “old” elements. Language plays a central role in the human brain, from how we process color to how we make moral judgments. It directs how we allocate visual attention, construe and remember events, categorize objects, encode smells and musical tones, stay oriented, reason about time, perform mental mathematics, make financial decisions, experience and express emotions, and on and on.
Indeed, a growing body of research is documenting how experience with language radically restructures the brain. People who were deprived of access to language as children (e.g., deaf individuals without access to speakers of sign languages) show patterns of neural connectivity that are radically different from those with early language exposure and are cognitively different from peers who had early language access. The later in life that first exposure to language occurs, the more pronounced and cemented the consequences. Further, speakers of different languages develop different cognitive skills and predispositions, as shaped by the structures and patterns of their languages. Experience with languages in different modalities (e.g., spoken versus signed) also develops predictable differences in cognitive abilities outside the boundaries of language. For example, speakers of sign languages develop different visuospatial attention skills than those who only use spoken language. Exposure to written language also restructures the brain, even when acquired late in life. Even seemingly surface properties, such as writing direction (left-to-right or right-to-left), have profound consequences for how people attend to, imagine, and organize information.
The normal human brain that is the subject of study in neuroscience is a “languaged” brain. It has come to be the way it is through a personal history of language use within an individual’s lifetime. It also actively and dynamically uses linguistic resources (the categories, constructions, and distinctions available in language) as it processes incoming information from across the senses.
Put simply, one cannot understand the human brain without understanding the contributions of language, both in the moment of thinking and as a formative force during earlier learning and experience. When we study language, we are getting a peek at the very essence of human nature. Languages—these deeply structured cultural objects that we inherit from prior generations—work alongside our biological inheritance to make human brains what they are.