Dejerine was born near Geneva, Switzerland, in 1849. At school he was not regarded as an outstanding student. He became interested in biology and comparative anatomy. At the age of twenty-two he went to pursue his clinical studies in Paris, where he was a pupil of Vulpian and was connected to the Salpetriere as well as the Bicetre. In 1910 he was elected ‘Professeur de clinique des maladies du systeme nerveux a ta Faculte de Medicine’ in Paris.Dejerine owed much to his wife, Augusta Marie Klumpke, whom he married in 1888. She had studied medicine in Paris and became the first woman to receive the title of ‘interne des hopitaux’ in 1887. When Dejerine died in 1917, having spent himself in the exhausting service of an army hospital, it was his wife who carried on the bulk of his work, both in practice and in research. Dejerine published studies on topics such as progressive muscular dystrophy, olivopontocerebellar atrophy, and the thalamic syndrome, but among aphasiologists he is best known for his studies on alexia.
In the second chapter of his book Semiologie des affections du systeme nerveux, entitled ‘troubles du langage’, written in 1914, Dejerine argued that there are four types of language disturbance: aphasis, dysarthria or anarthria, mutism, and stuttering. Only the first two are caused by brain damage. When disturbances of verbal communication, that is, the exchange of ideas between persons, exists, there are three possible causes:
- disturbance of intelligence: in this condition the patient cannot understand speech or written text: he can no longer reason in a concrete or abstract manner;
- lesion of language centers or connections with the sensoric or motoric apparatus, which he calls ‘les aphasies proprement dites’: intelligence is not affected in these cases;
- lesions of the bucco-pharyngo-laryngeal system, resulting in dysarthria or anarthria.
The concept of intelligence clearly plays an important role in this classification
scheme. Later in his book he argues that in cases of total aphasia “le deficit intellectuel est souvent plus marque que dans l’aphasie sensorielle ou motrice”. In fact the concept of intelligence as used by Dejerine is closely related to consciousness or alertness and to the possibility of inner speech. Intelligence is said to be affected if a patient cannot cooperate when he is tested.
Dejerin’s views on aphasia are perhaps best expressed in his definition: “laphasie est la perte de la memoire des singes aux moyens desquels l’homme civilise echange ses idees avec ses semblables”. Aphasis, therefore, is not restricted to spontaneously spoken language but to all the different ways in which verbal concepts can be expressed. Dejerine distinguished two major groups of disturbances on clinical and pathological grounds: sensory aphasia and motor aphasia.
Although Dejerine was well respected by his colleagues, his contribution to the area of aphasia lies more in his teaching of the ‘classical’ theories on language centers than in research. He attempted to fit all the different varieties of aphasia into a single scheme. From his somewhat polemic style of writing one gets the impression that an important purpose of his papers was to defend the views of authors such as Broca, Wernicke, and Kussmaul against the attacks of authors such as Pierre Marie, rather than to present a new model of language disorders.
Dejerine is well known for his study of specific reading and writing disorders after brain damage. After the introduction of the concept of sensory aphasia by Wernicke (1874) and the subsequent subdivision by Kussemaul to state that there are four ’centers’ in the left hemisphere that are involved in language disorders:
- the third frontal gyrus (Broca’s area): affected in motor aphasia;
- the posterior part of the first temporal gyrus (Wernick’s area): affected in word deafness;
- the gyrus angularis (‘pli courbe’): involved in word blindness (discovered by Dejerine);
- the foot of the second frontal gyrus (area of Exner): affected in agraphia.
The existence of the writing center (area of Exner) was later refuted by Lichtheim and Wernicke. Dejerine subscribed to their view: if a patient cannot write anymore, this is to be ascribed to a disturbance of the “inner speech’ and not to damage of the center for writing words. In 1891 Dejerine described two cases which support his position. The first case was a 63-year-old sailor who suddenly became word blind and agraphic. He could not read letters nor words except for his own name. There was no naming problem. For a month the patient made paraphasic errors. After 8 months the patient died and autopsy was performed. A yellow cone-shaped softening in the area of the gyrus angularis of the left hemisphere was found. The base was located in the cortex of the angular gyrus and the top was wituated in the ependym of the occipital part of the lateral ventricle.
One year later Dejerine published a second case: Thepatient was a 61-year-old intellectual and educated businessman. After several attacks lasting several minutes that gave rise to a numb feeling in his right extremities, he also perceived some difficulty in speaking. He then suddenly became word blind. He was seen by an ophtalmologist, who could not find any disturbance except for a slight right homonymous hemianopia and hemiachromatopia. The patient could not rade words or letters. Moreover, he could not recognize music notes, but had no difficulties with digits. Inner speech, color naming, singing, and calculation were intact. He could write spontaneously or to dictation. However, he was not able to copy from text. He could not produce the normal handwritten version of a letter shown to him in print. Tactile inspection of letters improved letter recognition. The patient reported that he could see in his mind the word he wanted to write but he could not read the same word after it was written down by him. Intelligence seemed intact as well as his ability to play cards. This condition remained stable for four years. After a period of agitation and depression his writing became irregular. He then became paretic on his right side and had articulation problems. The following day the paresis had disappeared but now he was clearly aphasic. The patient died ten days later.
At autopsy the right hemisphere was completely intact. In the left hemisphere tow types of lesions were observed. Firstly, there were two older lesions, one in the occipital cortex and one in the splenium. Secondly, a relatively fresh softening of the gray and white matter of the parietal lobe and the angular gyrus was found.
On the basis of these two cases Dejerine discriminated two forms of word blindness, resulting from lesions at two different sites.
- word blindness with agraphia: produced by a lesion of the angular gyrus, where visual images of letters and words are stored. This lesion gives rise to agraphia and possibly to paraphasia, due to the fact that the kinesthetic information is lost.
- Word blindness without agraphia, or pure word blindness: the lesion is located in the visual cortex. The patient cannot copy letters and words at will; however, auditory and muscle information can activate visual images, and therefore spontaneous writing and writing to dictation remain possible.
These two types of word blindness correspond with the cortical and subcortical forms of alexia dexcribed by Wernicke. By means of the same two studies, Dejerine came to the conclusion that the area of Exner could not be maintained as a center for writing. Another important argument against the notion of a writing center in Exner’s area was that patients with left frontal lesions can write if they use their left hand or foot.
After this period of synthesis and classification of the clinical types on the baise of aphasia and cerebral localization of the lesion responsible, discussions arose on the functional relations between these centers. As a sign of the times a mechanistic relation was elaborated. While Magnan believed that a primary role is played by the motor center in the mechanism of language pathology, Wernick ascribed a regulating role to the sensory center. Charcot and his followers, including Dejerine, on the other hand argued in favor of autonomy of the centers. Charcot explained the variation in which the aphasia is expressed according to the ‘psychic type’ of the individual person. This type is determined by education: education and study may make someone more motorically, visually, auditorily, or graphically oriented. According to Dejerine there are two mechanisms involved in the affection of language, namely lesions of cortical language areas and subcortical lesions that isolate the language centers from other parts of the brain. In the former case inner speech is usually lost. Pure word blindness is an example of the latter mechanism: association fibers between the visual center (occipital lobe) and the center for visual images of words are disconnected.