Intro arrow 0. Left & Right Brain arrow 0.5 Language Areas
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0.5 Left and right brain: Language processing

 How people comprehend ‘natural language’ like stories, texts, and conversations, Is a complex behavior, calling upon numerous cognitive and neural systems. A great deal of research has focused on how people decode written and spoken input into words, retrieve word meanings, and parse syntax.


For over a century, the consensus has been that frontal and temporoparietal regions (where the temporal and parietal lobes meet) of the Left Hemisphere (LH) are crucial for these fundamental language processes.


Recent investigating on how the brain converts a continuous stream of words into meaningful communication has proceeded more slowly, but is beginning to reveal how the brain comprehends natural language. One conclusion is that, as language input gets more complex, there is more involvement of Right Hemisphere (RH) homologues to classic LH language areas.

Evidence suggest that the Right Hemisphere (RH) also contributes to language comprehension:

1. A number of neuroimaging studies report, greater RH-activity than LH-activity while subjects perform higher-level language tasks, such as:

  • Comprehending metaphors.
  • Getting jokes.
  • Deriving themes, and drawing inferences.
  • Generating the best endings to sentences.
  • Mentally repairing grammatical errors.
  • Detecting story inconsistencies.
  • Determining narrative event sequences.
2. Patients with RH brain damage sometimes have subtle deficits in comprehending natural language.
3. Different semantic processing is manifest in distinct patterns of sensitivity to various semantic relations for words presented to the LH or RH, via the right or left visual hemifield. (semantic = relating to meaning)
4. The RH owns a number of very subtle ‘linguistic’ functions which are virtually synonymous with ‘poetry’ or ‘poetic’ speech. RH involvement in language is what differentiates ‘poetic’ or ‘literary’ from ‘referential’ or ‘technical’ speech and texts. (source: Poetry As Right-Hemispheric Language)

5. The RH sometimes support language recovery, not like patients grow new language areas in the RH, it seems more that RH language areas can become more finely tuned to perform tasks, normally performed by the LH:

  • Children with early brain damage, can recover most language abilities.
  • Some adult patients who recover from aphasia, due to LH brain damage, show increased processing in homologous areas of the intact RH.
6. The two hemispheres are anatomically more similar than different. There are size asymmetries in some language areas, but there don’t appear to be cortical areas or pathways that are present in the LH but absent in the RH. These known asymmetries might correlate with language function, but not perfectly.

What is the real difference between Left & Right hemisphere?


The main difference between LH and RH can be found at the micro-anatomical level. There are numerous asymmetries that support distinct computations within a process, conferring distinct advantages to each hemisphere:

  • The LH strongly activates small and focused semantic fields, containing information closely related to the dominant meaning of input word(s).
  • The RH weakly activates large diffuse semantic fields, including information distantly related to the words, providing only a coarse interpretation, insufficient for many language tasks.
  • Pyramidal neurons in RH language areas have longer initial dendritic branches and more synapses further from the soma. This causes RH neurons to receive a broader and more overlapping field of inputs. 
  • The LH cortical columns are more widely spaced, with less overlap among input fields.
  • The larger semantic fields of the RH are more likely to overlap, allowing weak activation to summate, when input includes multiple distantly related words. Therefore, the RH is sensitive to distant semantic relations, and comprehenders capitalize on this sensitivity when understanding natural language, particularly figurative language or unusual constructions.

These asymmetries are also consistent in cortical micro-circuitry of language areas that influence how neurons spread information. For example, at the cellular level, pyramidal cell dendrites branch further from the soma and ultimately into more branches with more dendritic spines, on average, in the RH than in the LH. Such circuitry favors more input from relatively distant sources in the RH, and from close sources in the LH.


This is a clip of how Neurons, branches and networks work:


 Because functional and structural levels of brain organization are interdependent, some effects at each level get passed through to higher levels. Thus, cortical mini-columns, macro-columns, and functional areas are more highly overlapping and more densely interconnected in the RH than in the LH. Overall, these microcircuitry asymmetries suggest broader input and projection fields, and greater functional overlap across processing units in the RH than in the LH. The images left are photomicrographs of microcolumnar and macrocolumnar structures in the human temporal cortex, where you can notice the columnar arrangement of pyramidal cells in the upper cortical layers. Bundles of afferent and efferent fibers traversing vertically between the columns of pyramidal neurons.


It is a huge leap from dendritic branching to natural language comprehension; but cognitive asymmetries exist in language processing, microcircuitry asymmetries exist in language areas, and semantic processing clearly requires neural activity.


• Bilateral brain processes for comprehending natural language

  by Professor Mark Jung Beeman, Ph.D source-pdf 

• Hemispheric asymmetries in cerebral cortical networks

  by Professors Jeffrey Hutsler and Ralf A.W. Galuske  source-pdf


The purpose of this site is to present questions and new ideas about the above subjects.

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