Language Production and Processing in the Human Brain
December 12, 2019
Philologists have long debated "how long ago" humans started talking to each other. Since words left no traces in the archaeological records of time, there is a shortage of direct evidence but estimates range from 50,000 years ago to as early as a couple million years ago. Comparisons between human language communication and the communication systems used by other primates suggested that both developed using signals, gestures and uttered sounds. However, human communication used both signals and symbols. Symbols being sounds that have specific meaning to a group of people. Unlike signals, symbols are not instinctual and must be both taught and learned.
Broca's Area of the Brain
During the mid-19th century, researchers realized that due to a lack of empirical evidence, scholarly debates over "when and where" language originated were based on speculation and were likely a waste a time. During this same period, a French neurosurgeon named Paul Broca was examining the brain of a recently deceased patient who had been able to understand the spoken language but was unable to speak a complete sentence and also was unable to express his thoughts through the written word. The autopsy revealed lesions in the posterior portion of the frontal lobe in the left hemisphere. Named Broca's area, this was the initial proof as to "how" language developed through the existence of a language center in the human brain.
Wernicke's Area of the Brain
A decade after Broca's discovery, a German neurologist named Carl Wernicke identified the ill effects of lesions in another part of the human brain. Although people with lesions in the posterior portion of the left temporal lobe (now known as Wernicke's area) were able to speak, their speech made no sense. Since Wernicke's area is responsible for the comprehension of speech, lesions at a junction of the parietal, temporal, and occipital lobes seriously impaired the development of language. People affected by Wernicke's aphasia were able to produce phrases that sounded fluent yet lacked meaning. While these utterances had a rhythm similar to normal speech, no information was relayed, so no language exists. Not surprisingly, Wernicke's aphasia affects both spoken and written communications.
Discovery of the Language Loop & Pathways
Once researchers understood that for a human to develop, use, and understand a language, several areas of their brain must function together, the central role of the arcuate fasciculus, or language loop, became a primary area of focus. This large bundle of nerve fibers is found in both the left and right hemispheres and play a key role in language processing as well as visuospatial processing. This network created by the language loop is one of the slowest regions to mature and undergoes a shift in lateralization during adolescence to allow for pragmatic abilities through more complex sentence comprehension and higher semantic processing. Using the latest MRI technologies, researchers now understand more about these complex connections, such as the dorsal language stream is concerned with phonology and the ventral language stream is concerned with semantics. Neural and behavioral research studies show that exposure to language in the first year of life influences the brain's neural circuitry even before infants speak their first words. However, verbal language is not the only way that people communicate with each other. Before someone opens their mouth to speak, they are already communicating through various non-verbal mechanisms. Nonetheless, in a majority of people, it is the left hemisphere that formulates and understands the meaning of words and sentences, whereas the right hemisphere of their brain interprets the emotional connotation.