IN the 1860s, the French physician Paul Broca treated two patients who had lost the ability to speak after suffering strokes. When they died, he examined their brains, and noticed that both had damage to the same region of the left frontal lobe. About a decade later, neuropsychiatrist Carl Wernicke described a stroke patient who was unable to understand written words or what was said to him, and later found in this patient's brain a lesion towards the back of the left temporal lobe.
Thus was established the classical neurological model, in which language is localized to two specific areas of the left hemisphere. Recently though, researchers have found evidence that some components of language are encoded in other brain regions. Furthermore, it is still unclear how the brain represents language in bilingual people. Some studies suggest that both languages are represented in the same set of laguage areas, while others point to distinct neural substrates for the first and second languages.
A unique case study published in the open access journal Behavioral and Brain Functions sheds some light on this matter. The study, by Raphiq Ibrahim, a neurologist at the University of Haifa, describes a bilingual Arabic-Hebrew speaker who incurred brain damage following a viral infection. Consequently, the patient experienced severe deficits in one language but not the other. The findings support the view that specific components of a first and second language are represented by different substrates in the brain.
The patient, referred to as M.H., is a 41-year-old high school biology teacher. A native Arabic speaker, he learned Hebrew at an early age (4th grade) and later used it competently both professionally and academically. He was proficient enough in the language to graduate from an Israeli university, at which he was taught in Hebrew. In 2004, M.H. was admitted to the local hospital with with a sudden onset of fever and confusion. His cerebrospinal fluid tested positive for Herpes simplex virus, and he was given the antiviral drug Zovirax. Two days later, he suddenly began to experience headaches, vomiting and disturbances of consciousness.
A CT scan showed that he had suffered a massive hemorrhage in the left temporal lobe, which was compressing the tissue on both sides of the central sulcus, the prominent gfissure which separates the frontal and parietal lobes. A craniotomy was performed to relieve the pressure, and afterwards another scan showed moderate hemorrhage and herpes encephalitis in the left temporal lobe, and another hemorrhage beneath the outer membrane (the dura) lying over the right frontal lobe. He began to recover, but two days after the operation became lethargic, and was sent to another hospital for rehabilitation. During his 2 month stay there, he developed epileptic seizures which originated in the left temporal lobe, and amnestic aphasia (an inability to name objects or to recognize their written or spoken names).
After the rehabilitation period, a series of linguistic tests was administered to determine the extent of his speech deficits. M.H. exhibited deficits in both languages, but the most severe deficits were seen only in Hebrew. In this language he had a severe difficulty in recalling words and names, so that his speech was non-fluent and interrupted by frequent pauses. He had difficulty understanding others' spoken Hebrew, and also had great difficulty reading and writing Hebrew. In Arabic, his native language, all of these abilities were affected only mildy. Differences were also seen in the effects of intensive language therapy. Although the therapy led to improvements in both languages, the improvements in Arabic were seen in all linguistic abilities; in Hebrew, by contrast, there was only mild improvement in his spontaneous speech and comprehension, and his ability to name objects remained unchanged.Similarly, his ability to read and write Arabic, but not Hebrew, improved significantly.
Most previous studies of bilinguals have used participants who speak English and one other Western European language. This is the first to investigate bilingualism in the Semitic languages, which differ markedly in structure from Indo-European languages. Nevertheless, it it provides valuable evidence about the mechanisms of lanuage processing in the bilingual brain. The results support a neurolinguistic model in which the brain of bilinguals contains a semantic system (which represents word meanings) which is common to both languages and which is connected to independent lexical systems (which encode the vocabulary of each language). The findings further suggest that the second language (in this case, Hebrew) is represented by an independent subsystem which does not represent the first language (Arabic) and is more susceptible to brain damage.
Related:
Ibrahim, R. (2009). Selective deficit of second language: a case study of a brain-damaged Arabic-Hebrew bilingual patient. Beh. Brain Funct. 5: 17 [Full text].
Brain & Behavior
Comments (13)
The varying and sundry aphasias and agnosias are really fascinating, in part because they tease out the various dissociations between tasks in the brain. Nice piece!
Posted by: Muse142 | July 10, 2009 9:04 PM