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Neurolinguistics is the science concerned with the neural mechanisms underlying the comprehension, production and abstract knowledge of language, be it spoken, signed or written. As an interdisciplinary endeavor, this field straddles the borders between neurology, linguistics, cognitive science, neurobiology, communication disorders, neuropsychology, and computer science. Researchers are drawn to the field from a variety of backgrounds, bringing along a variety of experimental techniques as well as widely varying theoretical perspectives. Through aphasiology, brain imaging and computer modeling, neurolinguists seek to elucidate how the brain processes language information. Neurolinguistics has highlighted the special role of that part of the human brain known as Broca's area in crucial aspects of human language, namely syntax: the component of language that involves recursion.

History

Broca's area and Wernicke's area

Historically, the term neurolinguistics has been most closely associated with aphasiology, the study of linguistic deficits occurring as the result of brain damage. Aphasiology, which was made famous by Paul Broca, attempts to make predictions about what linguistic functions are carried out in which parts of the brain by analyzing what language abilities are affected when an individual incurs brain damage to a specific localization in the brain. Aphasic research, also known as lesion-deficit research, led to the identification of Broca's area which was associated with language production deficits. Another aphasic discovery was Wernicke's area (named after Carl Wernicke) which was associated with deficits in comprehension.

Although aphasiology is the historical core of neurolinguistics, in recent years the field has broadened considerably, thanks in part to the emergence of new brain imaging technologies, such as PET and fMRI, which can highlight patterns of brain activation as people engage in various language tasks. Neurolinguistics is also closely related to the field of psycholinguistics, which seeks to elucidate the cognitive mechanisms of language by employing the traditional techniques of experimental psychology; today, psycholinguistic and neurolinguistic theories often inform one another, and there is much collaboration between the two fields.^{citation needed}

Neurolinguistics gained recognition as a distinct discipline with the creation of the Journal of Neurolinguistics in 1985. ¹

Brain imaging

 

Images of the brain recorded with PET (top) and fMRI (bottom)

Modern brain imaging techniques have contributed greatly to a growing understanding of the anatomical organization of linguistic functions. Such techniques include PET and fMRI, which provide high spatial resolution images of energy utilized in various brain regions during language processing tasks. Unfortunately, the techniques do not allow for high temporal resolution of brain activity as the comprehension or production of sentences unfolds.

As temporal resolution is of utmost importance in these questions, researchers also employ the gross electrophysiological techniques EEG and MEG. These provide resolution during milliseconds, but the exact nature of brain mechanisms generating the electrical signals on the scalp is not known, making them difficult to interpret. Consequently, EEG and MEG are used primarily to inform theories of the cognitive/computational architecture of language, without regard to their precise neurobiological implementation. For example, one might suspect that out of three categories of words that could end a sentence, two are actually tapping into the same mechanism, but the third is represented differently. Showing that these two categories elicit an identical electrophysiological response different from that of the third would support such a hypothesis. Some other important and commonly researched topics in EEG and MEG include the N400 brain response and the mismatch negativity.

Brain waves recorded using EEG

Among newer noninvasive techniques to study the workings of the brain, including how language works, transcranial magnetic stimulation (TMS) is becoming more important, although few neurolinguistic studies using this technique have been performed to date.² It is a method of exciting or interrupting brain activity in a specific and controlled location, and thus is able to imitate aphasic symptoms without causing long-term damage^{citation needed} and giving the researcher more control over exactly which parts of the brain will be examined. As such, it is a less invasive alternative to direct cortical stimulation, which can be used for similar types of research but requires that the subject's scalp be removed, and is thus only used on individuals who are already undergoing a major brain operation (such as individuals undergoing surgery for epilepsy.^{citation needed}

Computer modeling

One other important methodology in the cognitive neuroscience of language is computational modeling, which can demonstrate the plausibility or implausibility of specific hypotheses about the neural organization of language while generating novel predictions for further empirical research. Rather than deriving a mathematical analytical solution to the problem of language, experimentation with computational modeling is done by changing the parameters of the system in a computer, and studying the differences in the outcome of the experiments. Theories about the brain's computations can then be deduced from these computational experiments. Currently, computational modelers are collaborating increasingly with brain imagers and psychologists in coordinated, interdisciplinary programs of research. Such programs have yielded important new insights into the nature of language, as well as major language disorders affecting millions, such as stuttering and dyslexia.

Further reading

Relevant journals are Journal of Neurolinguistics and Brain and Language. Both are subscription access journals, though some abstracts may be generally available.

References