Broca, P. “On the site of the faculty of the articulated speech” The meeting of the Anthropological Society, 1865.
Broca is a name known universally amongst neuroscientists, med students, linguists, and really almost anyone who’s ever had an interest in language and the brain. Broca lends his name to Broca’s area, an area of the brain localized to the pars triangularis of the inferior frontal gyrus (in English: the area in the shape of a rough triangle that is on the left side of the brain, in the frontal lobe, and it’s on the side just above the tip of the temporal lobe…crap, I’m just including a picture). Broca’s area, along with Wernecke’s area, is always localized to just one side of the brain, usually the dominant side, or the one controlling the handed side of the body. This means, for right handed or ambidextrous people, Broca’s area is on the left side, and for left handed dominant people, it may occur on the right.
So what IS Broca’s area? It is the area of the brain primarily involved in speech, and language processing (as opposed to Wernicke’s area, which is involved in language comprehension). People with damage to Broca’s area suffer major deficits in language production. They can understand you perfectly, can read perfectly well, their motor skills with their mouth, vocal chords and tongue are usually all right, and they express their thoughts on paper just fine, but they cannot TELL you what they mean. Patients with damage to Broca’s area are completely unable to form complex sentances. There is a disconnect between the word they need to form and the motor sequences needed to produce the sounds. Often they can manage sentances that are simple, and usually described as telegraphic, with nothing more than content words.
This means that someone trying to say “My sister and I went out for ice cream today” might come out something like this: “Today…sister…me…ice cream”. People with Broca’s aphasia (‘aphasia’ or ‘aphemie’ was a word Broca used for those who were unable to produce language) are usually very aware that they can’t speak properly, but they are unable to correct the problem. You can imagine how horribly frustrating this is for people who suffer from aphasia. The problem is that Broca’s area is very close to the primary motor cortex, and controls the muscles required for vocalization. So though the muscles themselves are fine, the brain connections to them are not.
Broca first laid out his concept of aphasia in 1861, when the idea of brain localization was just beginning to come back into style. The concept of localization of certain functions in certain areas of the brain has been out of fashion for a while, mostly due to the study of phrenology. Phrenology was a quack science, wherein people would try to determine your personality traits by feeling the bumps and curves of your skull. They claimed that certain shapes in certain areas were responsible for things like intelligence or morality. Of course this stuff is ridiculous, but it left a pretty bad taste in scientists’ mouths for the study of brain localization.
(Paul Broca, courtesy of of nature.com)
However, brain localization concepts soon began to make a comeback. Broca was not the first to look for the brain localization of language, Bouillaud was there before him, claiming that speech was localized to the frontal lobes. At first, Broca disagreed, believing that changes in speech production would involve global brain changes, not lesions localized to a specific area.
So when Bouillaud’s son-in-law Aubertin challenged Broca at the meeting of the Anthropological Society in 1861, Broca offered up his star patient, Tan, as proof. Tan was a patient in the Bicêtre Hospital, Leborgne, whose aphasia was so severe that he was unable to pronouce any word except for “tan”. Aubertin accepted Broca’s challenge. If Tan did NOT have a frontal lesion in the brain, Aubertin would never back Bouillard’s localization ideas again.
When Tan died several months later, Broca did an immediate autopsy. He found that Tan had considerable loss of brain substance (probably from syphillis), but, more importantly, he found a lesion in the left frontal lobe. Broca immediately changed his views, declaring Bouillard’s theory to be correct, that “the loss of speech…was a consequence of a lesion of one of the frontal lobes”.
Of course this was only one patient, and did not address whether the whole frontal lobe was required for speech, or just a part. So over the next four years, Broca undertook a study of over 25 patients with aphasia, trying to find the seat of language. What he found was at first extremely controvesial. He found that in every single case of aphasia he looked at, there were lesions to the left inferior frontal lobe. He concluded that the left inferior frontal lobe was the area principally concerned with the articulation of speech, and gave his initial findings in 1863.
This doesn’t sound too out there to us now, but at the time it caused a lot of controversy. The problems wasn’t the localization to the inferior frontal lobe, it was Broca’s claim that it was the LEFT inferior frontal lobe. This didn’t sit well with a lot of scientists at the time. It was pretty accepted that, when you had two sides or halves of an organ, the both acted in the same way. Both kidneys do the same thing, both sides of your lungs, and both of your ovaries or testes. Your legs and arms will do essentially the same thing, though due to handedness (or footedness), you may have more strength or dexterity on one side. Therefore, if the left part of your brain was involved in language, the right must be also.
Broca insisted that this wasn’t the case, and he gave his famous defense in 1865. Many of his patients had partial paralysis of the right side, adding credence to the idea that the left side of the brain was at fault. He also laid out extensive hypotheses as to why the left side of the brain controlled speech articulation. He found that people with lesions of the right inferior frontal gyrus did not generally display language impairments, adding strength to the idea fo the left side as the center of language articulation. Broca thought that language was localized to the left brain primarily in patients who are right-handed, and that for those who are left-handed and therefore right-brained, the language area might well lie in the right hemisphere.
He cites the case of a woman who suffered epilepsy through much of childhood. Her right side was underdeveloped, and she did everything with her left hand. She was of average mental abilities and able to speak coherantly without a problem. When she died (age 47), they found that the left side of her brain lacked the sylvian artery, and so had little to no blood flow. So the left side of her brain was atrophied, with the size of her frontal lobe on that side “the size of rat gut”. The left side of her brain weighed only 297g. In contrast, the right side of her brain (controlling the left side of her body, which she was able to use throughout her life) was fully developed and weighed 540g. Broca hypothesized that, because she lost the left side of her brain early in development, her language center was reorganized to the right side of the brain, a type of neuronal plasticity.
However, he also noticed that people who lost Broca’s area due to a lesion later in life were usually able to regain speech only to a very limited degree. Broca thought that this was due to several factors, such less neuronal plasticity after childhood, less time spent on regaining the ability, and that other abilities lost in the lesion might preclude the ability to relearn language.
Broca’s final conclusion was that
“The two halves of the encephalon, being perfectly identical from an anatomical point of view, cannot have different functions, but the more precocious development of the left hemisphere makes us prone…to execute with that half of the brain the manual and intellectual actions that are most complex.”
Of course, there are lots of drawbacks to Broca’s studies at the time. He worked in aged patients, many of whom had pretty extensive lesions that covered far more than just the inferior frontal gyrus. Also, as pointed out by his contemporary, Jackson “to locate the damage which destroys speech, and to locate speech are two different things”. More recent work has shown that damage to Broca’s area results in aphasia can be recovered within a matter of weeks, as plasticity takes over. Furthermore, a new study on Broca’s primary brains (the ones he used to illustrate his hypotheses and preserved for future studies), show that Broca’s area might be located a bit more anterior (toward the front of the brain) than first thought. Also, the damage to the brains extended a lot deeper into the cortex than first thought, which may have contributed to the speech problems of the patients. These new finding notwithstanding, Broca’s work is still considered to be outstanding, a classic example of clinical symptoms contributing to the elucidation of brain function.
Work with Broca’s are continues to this day. Studies with fMRI have found decreases in Broca’s area activity in people who stutter, and there have been many studies conducted on the skulls of Homo habilis and australopithecus to determine when the brain areas for language evolved.
Of course it just figures that right after I finish this post, I find that Neurophilosophy was there before me, in a post he did on his old wordpress blog on Paul Broca’s life and work, as well as the modern findings with Broca’s area. He’s got a great post, with some good pictures of brains with inferior frontal lesions. Check it out if you’re scicurious!
Berker, E.A., Berker, A.H., Smith, A. (1986). Translation of Broca\’s 1865 report. Localization of speech in the third left frontal convolution.. Archives of Neurology, 43(1), 1065-1072.
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