Is Broca still relevant today?

Wednesday 19 December 2012

It is amazing to me that students are still writing about Paul Broca's research from the 1800's.  Considering how much research has been done on the brain in the past 20 years, it seems rather unreasonable that students choose to demonstrate their knowledge of the biological level of analysis by writing about a study that is over 150 years old. 

Seeing that this study has apparent interest for students, I feel it is important to update students on where we are with Broca's area.  The bottom line is - today Broca's findings have been challenged; some would argue that they have been refuted. Recent findings with language-impaired patients have suggested that other regions also play a role in speech production.

Obviously, when Broca did his research, he did it on a very small sample.  There were two historic patients on which the claims for the role of the Broca's area were based. In addition, the only way he had to map the brain was through post-mortem research, which is rather limited compared to the technology that we have today.  Dronkers et al (2006) examined the brains of these two famous patients using a high-resolution MRI.  It appears that the absence of speech cannot be attributed to lesions in the Broca's area alone. In fact, the region which was damaged in the patients is not precisely the same region that we today know as the Broca's area. 

These findings are important; they may help to explain why damage limited to the cortext of the Broca's Area does not appear to produce Broca's aphasia.  It appears that the damage must extend to the surrounding regions of the frontal lobe and the underlying white matter.  

Another study appears to show the role of genetics in language development. Watkins et al (2002) studied three generations of the KE family, half of whose members are affected by a severe speech and language disorder caused by mutation of a single gene found on chromosome 7. The mutation appears to cause abnormal development of the caudate nucleus and the left inferior frontal cortex, including Broca's area.

Wernicke (1874) suggested that the Broca's area contains motor memories - that is, memories of the sequences of muscular movements that are needed to articulate words.  But Broca's aphasia is more complex than this. There are three major speech deficits that are produced by legions in and around the Broca's Area: agrammatism, anomia and articulation difficulties.  Agrammatism is the inability to produce grammatically correct speech.  Anomia is the inability to name persons or objects.  These problems cannot be explained by Wernicke's original conclusions.

In addition, Dronkers (1996) has found that apraxia - the inabilty to produce speech because of the inability to control the movement of the tongue, lips and throat - is due to damage to the insular cortex, not the Broca's area.

So, the bottom line is that it appears that Broca oversimplified the process of speech production and that the argument for localization of function is a rather reductionist approach to such a complex human behaviour.  I would like to suggest that if Broca is a part of our curriculum, that we help students to understand the role of this study in the 21st century and show them the complexity of the interaction between our physiology and psychology.

Tags: Broca, Broca\'s area, localization, brain, language, aphasia, agrammatism, anomia, stroke, MRI


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