3.1. Fields of research

Neurolinguistics research is carried out in all the major areas of linguistics. The main linguistic subfields and the ways neurolinguistics addresses them are given in the table below.

Subfield	Description	Research questions in neurolinguistics
Phonetics	the study of speech sounds	how the brain extracts speech sounds from an acoustic signal, how the brain separates speech sounds from background noise
Phonology	the study of how sounds are organized in a language	how the phonological system of a particular language is represented in the brain
Morphology and lexicology	the study of how words are structured and stored in the mental lexicon	how the brain stores and accesses words that a person knows
Syntax	the study of how multiple-word utterances are constructed	how the brain combines words into constituents and sentences; how structural and semantic information is used in understanding sentences
Semantics	the study of how meaning is encoded in language

Neurolinguistics investigates several major topics, including (a) where language information is processed, (b) how language processing unfolds over time, and (c) how brain structures are related to language acquisition and learning. Research in the first language acquisition has already established that infants from all linguistic environments go through similar and predictable stages, and some neurolinguistics studies attempt to find correlations between stages of language development and stages of brain development, while other studies address the problem of the physical changes (known as neuroplasticity) that the brain undergoes during second language acquisition, when adults learn a new language. One of the highlights of neurolinguistics is speech and language pathology related to the language areas in the brain and considered by aphasiology.

3.2. Language areas. Aphasias

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eurolinguistics is rooted in the 19th century aphasiology, or the study of aphasias as linguistic deficits occurring as the result of brain damage. Aphasiology correlates a brain structure to a brain function by analyzing the effect of brain injuries on language processing. One of the first people to connect a particular brain area and language processing was Paul Broca (1824-1880), a French surgeon who conducted autopsies on numerous individuals with speaking deficiencies, and found that most of them had brain damage (or lesions) on the left frontal lobe (лівій лобовій частці), in the area now known as Broca's area.  Right-handed individuals have this area in front of, and slightly above, the left ear. Later, the German neurologist Carl Wernicke (1848-1905) discovered another language center, named Wernicke's area after him. It is located under and surrounding the left ear (Fig. 3.3).

Fig. 3.3. Broca’s and Wernicke’s areas hemisphere of the human brain.

The findings of Broca and Wernicke established the field of aphasiology and the idea that language can be studied through examining physical characteristics of the brain. Initial research in aphasiology also benefited from the early 20^th-century work of Korbinian Brodmann, who made a ‘map’ of the brain’s surface dividing it up into numbered areas based on each area's cell structure and function; these areas, known as Brodmann areas, are still widely used in neuroscience today.

Broca’s and Wernicke's areas are specialized for different linguistic tasks. Broca's area handles the motor production of speech, and Wernicke's area handles auditory speech comprehension. Damage of these and some other areas causes different kinds of aphasia.

• Broca’s aphasia influences speech production, while comprehension of speech may be unimpaired. This aphasia type is characterized by slow, effortful speech, because of which it is also called expressive aphasia. In speech mostly content words (nouns, verbs, and adjectives) are produced; function words (determiners, prepositions, pronouns) are often omitted. Thus, the speech appears to be without grammar (agrammatism). This speech style is called telegraphic speech. In many speakers with Broca’s aphasia, articulation is affected as well, because the brain site responsible for articulation is close to Broca’s area. Comprehension of spoken language is relatively good: in conversations, speakers with Broca’s aphasia understand what is said. When tested for the comprehension of complex syntactic structures, the performance drops dramatically. It is therefore assumed that in Broca’s aphasia the grammatical component of language is affected. Reading and writing are also impaired, comparable to oral comprehension and production

• Wernicke’s aphasia is characterized by difficulty in comprehending speech, and by the production of speech which is fluent but empty of meaning (fluent aphasia). Speech production is fluent and well-articulated, but the aphasic speaker produces sound and word substitutions, so-called ‘paraphasias’, for example ‘spool’ for ‘spoon’ or ‘mother’ for ‘wife’. Distortions of words may be further away from the target words than in these examples, and as a consequence the listener may not recognize existing words; these sound strings are called ‘neologisms’, for example, ‘stroofel’. When many of these words are produced, the text will no longer be understandable, which is referred to as ‘jargon’ or ‘word salad’. Comprehension of language is moderately to severely impaired. The combination of a severe comprehension and production disorder results in poor communication abilities. Writing and reading are parallelly affected.

• Anomic aphasia has no clear lesion site in the brain that is responsible for this aphasia type, but the lesions (damages) are usually found in the temporal and/or parietal lobe (скронева та/або тім'яна частка). Anomic aphasia is characterized by word-finding problems. The oral output of a speaker with anomic aphasia is basically fluent, but due to the pauses that arise from the word-finding problems, speech rate may be low. The word-finding problems are not only recognizable by pauses, but also by the use of less specific words, such as ‘thing’, ‘do’, ‘here’, ‘there’. The latter is called ‘empty speech’. Comprehension of spoken language is relatively good, although complex commands are difficult to understand. Reading is usually spared as well, but in writing the word-finding problems show up again.

• Conduction aphasia was first described by Carl Wernicke. The name of the syndrome derives from the fact that it is caused by a lesion in the tract that connects Wernicke’s and Broca’s area. It is characterized by the production of sound errors, for example, ‘scrample’ for ‘scrabble’. The patient is well aware of his errors and this results in many self-corrections, for example, ‘scramble, no strapple, no stample …’. The errors are particularly prominent when the patient is asked to repeat longer words and sentences. Comprehension of spoken and written language is relatively good, but impaired for complex and long sentences. In writing, a similar error pattern is shown as in speaking.

• Global aphasia is caused by the lesion which is often considerable and extends to both the frontal, temporal, and parietal lobes (лобної, скроневої і тім'яної часток). All language modalities are severely impaired. Spoken output is often restricted to one- or two-word utterances, sometimes only ‘yes’ and ‘no’, not always used correctly. Comprehension is severely impaired and reading and writing are hardly possible. This, of course, results in very poor communication abilities.

Although this classification has contributed considerably to the understanding of aphasia, most patients suffer from a ‘mixed’ form of aphasia, which cannot be labeled with any of the types mentioned above.