General Neuroscience

The Role of The Right Hemisphere in Language

Lorrayne Isidoro Gonçalves


Introduction

Before the breakthroughs of Broca and Wernicke, the notion of language regions was based on observations in patients with brain injuries. This was not able to directly determine the brain areas in which language is localized. This researchers studied their patients and found that certain parts in certain regions lead to damage to language.

 

 

Confirmation of Language Lateralization

Broca

    Paul Broca is known for his role in the discovery of specialized functions in different areas of the brain. In 1861, he was able to show, using post-mortem analysis of the patient Mr Leborgne (figure II), who had lost the ability to speak, that such loss was associated with damage to a specific area of the brain. The area, located toward the front of the brain's left hemisphere, became known as Broca's area [2].



 

Figure II: Damage in broca’s area of the Mr Leborne, the Broca’s patient

 

Wernick

    Carl Wernicke believed that abnormalities could be localized to specific regions of the cerebral cortex and thus could be used to determine the functions of these regions. Wernicke was one of the first to conceive of brain function as dependent on neural pathways that connected different regions of the brain, with each region contributing a relatively simple sensory-motor activity [3]. In view of this, the thoughts all were facing to the localization of the brain functions.

Definitive evidence supporting the inferences from neurological observations came from studies of patients whose corpus callosum and anterior commissure had been severed. This surgery is used for a treatment for epileptic seizures-disturbance in the electrical activity- of the brain called corpus callosotomy [1].

 

Corpus callosotomy

    Corpus callosotomy (figure IV) is an operation that severs - cuts- the corpus callosum, interrupting the spread of seizures from hemisphere to hemisphere. Seizures generally do not completely stop after this procedure - they continue on the side of the brain in which they originate. However, the seizures usually become less severe, as they cannot spread to the opposite side of the brain [4].

Figure IV: Corpus callosotomy

 

New Ideas

    So, in these patients, since the major axons connecting the cerebral hemispheres had been cut, researchers were able to determine what a “split” brain can result in. Roger Sperry and his group of research initiate the first investigations in split-brain patients were carried out by and established the hemispheric lateralization of language- localization of functions in the brain, normally divided into hemispheres-demonstrating many other functional differences between the left and right hemispheres  and continues to stand contributions to the understanding of brain organization [1].

 

Stereognosis Test

    Single-handed, vision-independent stereognosis - ability to identify an object by touch- can be used to evaluate the functional capacity of each hemisphere in split-brain patients.  In this test, it is essential to provide information to one side of the brain only (figure V). The scientists Sperry, Michael Gazzaniga, and others devised several simple ways to do this, the most straightforward of which was to ask the subject to use each hand independently to identify objects without any visual assistance. [1]

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Figure V: Stereognosis test

 

Tachistoscopic Presentation

    Visual stimuli or simple instructions can be given independently to the right or left hemisphere in normal and split-brain individuals. Since the left visual field is perceived by the right hemisphere , a briefly presented tachistoscopic (figure VI) instruction in the left visual field is appreciated only by the right brain assuming that the individual maintains fixation on a mark in the center of the viewing screen. In normal subjects, activation of the right visual cortex leads to hemispheric transfer of visual information via the corpus callosum to the left hemisphere. In split-brain patients, information presented to the left visual field cannot reach the left hemisphere, and patients are unable to produce a verbal report regarding the stimuli. However, such patients are able to provide a verbal report of stimuli presented to the right visual field. Awide range of hemispheric functions can be evaluated using this tachistoscopic method, even in normal subjects. [1]

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Figure VI: Tachistoscopic Presentation

    The results were intriguing: using the left hemisphere, split-brain patients were able to name objects held in the right hand without difficulty. In contrast, and quite remarkably, an object held in the left hand could not be named! Using the right hemisphere, subjects could produce only an indirect description of the object that relied on rudimentary words and phrases rather than the precise lexical symbol for the object (for instance, “a round thing” instead of “a ball”), and some could not provide any verbal account of what they held in their left hand [1].

    This shows further that the left hemisphere can respond to written commands, whereas the right hemisphere can typically respond only to nonverbal stimuli - e.g., pictorial instructions, or, in some cases, rudimentary written commands. These distinctions reflect broader hemispheric differences summarized by the statement that the left hemisphere in most humans is specialized for (among other things) the verbal and symbolic processing important in communication, whereas the right hemisphere is specialized for (among other things) visuospatial and emotional processing [1].

    This work on split-brain patients modified the thoughts about language lateralization; neuroscientists began to conclude that in most individuals, the left hemisphere is unequivocally the seat of the major language functions.

    It would be more accurate to say that we understand language and speak much better with the left hemisphere than with the right. [1] Because the major importance of the right hemisphere is nonverbal abilities--nonverbal communications include facial expression, the tone and pitch of voice, gesture, body language.  The summation of all of these elements, in fact, makes us really understand what another person wants to communicate.

 

The Role of the Right Hemisphere in Language: Understanding language process

    In contrast to the left hemisphere, the right hemisphere does not normally have much responsibility for linguistic processes such as phonology, morphology and syntax. It is best manner to view this, it is observing damages in the left hemisphere regions like Broca’s  and Wernicke’s areas. Damage to Broca's area primarily results in speech production impairment and loss of grammar and function words. In patients with lesions in Wernicke's area may speak fluently and use function words. Their problems mainly concern in syntax and lexical words, which leads to difficulties with understanding language as well as with producing comprehensible sentences.[9] They produce problems in comprehension and production of language.

    So, what is the function of the right hemisphere? When word meanings are accessed, semantically related word meanings are activated in both the left and right hemispheres. However, a vast set of related meanings remains accessible within the right hemisphere; into the left hemisphere only the most relevant meanings are maintained. This suggests that the right hemisphere is important for maintaining multiple meanings of ambiguous words, distant semantic associations of words, and broader aspects of meaning comprehension. Such functions may be important for the ability to revise initial interpretations of words or phrases, maintaining discourse coherence, and understanding multiple levels of meaning [5].

    Unlike the aphasias -  an inability to comprehend and formulate language because of dysfunction in specific brain regions-  caused by left hemisphere damage and generally resulting in focused language deficits, right hemisphere brain damage can result in a variety of diffuse deficits which complicate formal testing of this disorder. These formal tests assess areas such as understanding humor, metaphors, sarcasm, facial expression, and prosody- that impart additional meaning to verbal communication. This elements helps in a complete understanding of what is talked.

 

‘Extra’ elements in language

    This “coloring” of speech is critical to the message conveyed, and in some languages (e.g., Mandarin Chinese) is even used to change the literal meaning of the word uttered. These deficiencies, referred to as aprosodias - is a neurological condition characterized by the inability of a person to properly convey or interpret emotional prosody - are associated with right-hemisphere damage to the cortical regions that correspond to Broca’s and Wernicke’s areas and associated regions in the left hemisphere. The aprosodias emphasize that although the left hemisphere (or, better put, distinct cortical regions within that hemisphere) figures prominently in the comprehension and production of language for most humans, other regions, including areas in the right hemisphere, are needed to generate the full richness of everyday speech [1].

    Reading comprehension requires, in most cases, the processing of literal and nonliteral information, that is, explicit and implicit.  In addition, the participation of both hemispheres in this process is undeniable, since the left hemisphere tends to be involved in local coherence and in the aspects of the context (figure VII).[6] While areas of the right hemisphere seem to be more involved in global coherence, message macrostructure and inferential generation.

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Figure VII: Understanding language by non literal elements

 

    Overall, it would be erroneous to assume the right hemisphere has no language capacity. As noted above, in some individuals the right hemisphere can produce rudimentary words and phrases, and it is normally the source of emotional coloring of language. Moreover, the right hemisphere in many split-brain patients understands language to a modest degree, since these patients can respond to simple visual commands presented in tachistoscopic to the right hemisphere (in the left visual field) [1].

    Thus, the right hemisphere is the primary mediator of understanding a meaning of a sentence. These higher order language functions are crucial to understanding someone's true communicative intent and thereby integrating effectively into society.[8] How something is said may be just as important as what is said. In addition, it is important to note that the left and right hemispheres have a complementary work; they assume differents functions, complementing each other and not only dominance on one side of the brain in relation to the other. Therefore,  the language process is very elaborate. They are complex connections and together, they collaborate with their own and so important characteristics. All of this process is not only by right or left hemisphere parts. It is a work group!


References


  1. Martensson, Frida. (2007). Lateralization of Language Functions in the Human Brain.Neuro Linguistics. http://course.sol.lu.se/FON218/Postrar_neurolingvistik_VT07/Frida_Maartensson.pdf. Retrieved: 11/27/16.

  2. Mitchell, Rachel and Crow, Tim . (02/03/2005).Right hemisphere language functions and schizophrenia: the forgotten hemisphere? Brain, a journal of neurology. http://brain.oxfordjournals.org/content/128/5/963. Retrieved: 11/27/16.

  3. Mannell, Robert. (DD/MM/YYYY). Introduction to Prosody Theories and Models. Macquarie University, Sidney Australia. http://clas.mq.edu.au/speech/phonetics/phonology/intonation/prosody.html. Retrieved: 11/25/16.

  4. Jerônimo, G. (07/2012). The processing of reading and specificities of the cerebral hemispheres. https://www.researchgate.net/publication/270051021_O_processamento_da_leitura_e_as_especificidades_dos_hemisferios_cerebrais. Retrieved: 11/24/16.

  5. National Science Foundation,U.S.-Israel Binational Science Foundation, and the National Institutes of Mental Health. Title of the Sourced Material. Cognitive Neuroscience Lab. http://faculty.ucr.edu/~chrisc/research/research_RH.html. Retrieved: 11/21/16.

  6. Lava, Neil. (24/07/2016).Epilepsy and the Corpus Callosotomy. Web MD. http://www.webmd.com/epilepsy/guide/corpus-callosotomy. Retrieved: 11/21/16.

  7. Free encyclopedia. Carl Wernicke - Describes Wernicke's aphasia, Describes Wernicke's encephalopathy. The JRank Psychology Encyclopedia. http://psychology.jrank.org/pages/652/Carl-Wernicke.html. Retrieved: 11/21/16.

  8. Free encyclopedia. Pierre Paul Broca.The JRank Psychology Encyclopedia. http://psychology.jrank.org/pages/97/Pierre-Paul-Broca.html. Retrieved: 11/21/16.

  9. Purves, Dale. (11/03/1938). Neuroscience. Neuroscience. Chapter 26 -Language and Speech . Retrieved: 11/21/16.

Lorrayne Isidoro Gonçalves

Lorrayne Isidoro Gonçalves


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