to compare his left- and right-side cases or chose not to mention the difference. Marc Dax, in a paper written in 1836, actually proposed that the left hemisphere was the speech side after observing that aphasic patients more often have right than left hemiplegia. Dax prepared his paper for a medical society meeting but, evidently, never delivered it, and it remained unknown and unheralded until his son, Gustave, published it in 1865, along with his own report on the same subject ([24, 25]; for reviews, see Finger and Roe [26]; Joynt and Benton [27]).
What Was the Underlying Deficit?
Leborgne could not speak, but what was the underlying deficit? To understand Broca’s answer, we must consider the state of theory and evidence on another issue – the motor excitability of the cerebral cortex. In the 1860s, this was still unknown. No one, that is, had distinguished between an anterior “motor” region and a posterior “somatosensory” region, approximately encompassing, respectively, the pre- and post-central gyri. That revelation came later, most importantly in 1870 from Fritsch and Hitzig’s [28] experiments on dogs, and, in 1873, from Ferrier’s [29] experiments on monkeys. Until then, the cortex was seen as purely for mental acts, with the “motor” centers lying below in the corpus striatum and other basal ganglia. In 1864, it was how John Hughlings-Jackson explained the frequent co-occurrence of right-hemiplegia with speech loss:
The seat of the faculty of (speech) is near the upper part of the motor tract – the corpus striatum; so that, from mere relation of contiguity, (speech and motor functions) often suffer together ([30], p 39).
Broca [17] saw Leborgne’s symptoms the same way. His lips and tongue were not paralyzed because he could use them for other acts, but he could not remember how to use them for speech. In declaring that we speak with the left hemisphere and in locating its seat in F3, Broca meant it was where memories were stored for performing linguistic-articulatory acts. Leborgne’s aphasia, therefore, was a memory disorder. What was a motor disorder was his hemiplegia, signifying that his lesion extended into the corpus striatum, “the motor organ nearest the anterior lobes” (p 347).
The Left Hemisphere Is Not the Seat of All Language Functions
Broca [17] did not credit the left hemisphere with all language functions: the patient has “generally lost only the ability to reproduce the articulate sounds of the language”; he still understands “what is said to him and, consequently, understands the relation between ideas and words.” Leborgne, for one, seemed to understand “nearly (everything) said to him” (p 345). The “faculty of creating those relations (thus) belongs simultaneously to (both) hemispheres … but the faculty of expressing them by coordinated movements … would appear to belong only to one,” “nearly always … the left” ([20], p 386).
Comprehension and the Temporal Lobe
Broca was correct to link speech loss (later called motor, or non-fluent, aphasia) to left-hemisphere dysfunction, but he was mistaken if, in stating that comprehension belongs “simultaneously” to both hemispheres, he meant “equally.” Further studies of persons with comprehension deficits showed that here too the left hemisphere had a special role (e.g., Bastian [31]; Broadbent [32]).
The most revealing accounts came in 1874 from Carl Wernicke (Fig. 3, [33]), then a 26-year-old medical student. His first patient, Suzanne Adam, after falling ill from an unknown cause, could “comprehend absolutely nothing … said to her.” Her speech, though fluent, was confused, with “meaningless, garbled words” and paraphasias, although the overall meaning was “graspable in a general way” (quoted in translation in Eggert [34], p 120). Wernicke traced the symptoms to a posterior lesion in the superior temporal lobe on the left side.
Fig. 3. Carl Wernicke (1848–1905). From Galerie Hervorragender Ärzte und Naturforscher. J.F. Lehmanns Verlag, 1893. Public Domain.
Dementia or Aphasia?
In the past, as Wernicke noted, persons with fluent but confused, unintelligible speech were often diagnosed as demented or psychotic, especially those without paralysis or other physical signs of brain injury. Adam herself initially was diagnosed with dementia and placed in a psychiatric ward. Clarification of the symptoms would be important for diagnosis and nosology as it came to be understood that, at least in some cases, like Adam’s, the symptoms, in the absence of general dementia, were neurological and that the patients had another kind of aphasia, later to be called sensory, or fluent, aphasia.
Cerebral Dominance
The discoveries of the left hemisphere’s role in speech and comprehension were followed by reports linking it to other language skills, including Dejerine’s report in 1892 [35] on reading and writing. All such evidence eventually fostered the concept of “cerebral dominance,” implying that the left hemisphere was “dominant” not just for language but for all higher-order functions, including reasoning and abstract problem-solving, with the right hemisphere, to use Benton’s[36] phrase, as the “for the most part silent partner” (p 7), able to do some of the same things but not as well. In 1900, Liepmann [37]) proposed that the left hemisphere also was responsible for planning and coordinating sequences of skilled movements, or praxis. Given their differences in status, the two sides began to be called “major” and “minor.”
Right-Hemisphere Specialization
“Objects, Places, Persons, &c.”
Along with language disorders being so obvious and debilitating, this elevated view of the left hemisphere may help explain why it took longer to appreciate that the right had powers of its own. A breakthrough came in 1874 [38] when Hughlings-Jackson (Fig. 4) reported that persons with right-hemisphere injuries, but now posterior, had deficits in “recognition of objects, places, persons, &c.” (p 70). Note the similarity in names to Gall’s faculties of “place,” “space,” and “person.” Gall, of course, saw the faculties and their corresponding organs, like those for language, as identical pairs, one to each side.
