The key consequence of the first stroke was to interrupt tracts coursing from visual cortex in the occipital lobes to the left angular gyrus. For Dejerine, the left angular gyrus was a center interposed between visual cortex and the auditory center for words (Wernicke’s area) in the temporal lobe, wherein “the visual image of letters simultaneously arouses the auditory image and the articulatory image” (p 87) [35]. The auditory word center was linked to the frontal lobe center for motor articulation (Broca’s area). Angular gyrus destruction led to both alexia and agraphia. Dejerine suggested that letters of a specific word evoked meaning through connections between the left angular gyrus and other parts of a left hemisphere “language zone.”
Deconstruction
In 1906, the dominant Broca-Wernicke-Dejerine paradigm was unexpectedly and doggedly assailed by Pierre Marie (1853–1940) [36, 37]. Marie had trained with both Broca and Charcot, and later he succeeded Dejerine to Charcot’s neurology chair at the Salpêtrière. Marie did not accept the dogma of cerebral centers specialized for language. He pointed out that during the long course of human evolution and culture, reading and writing were relatively recent developments. It was illogical to presume that specialized centers had evolved for these purposes [38]. Marie acknowledged but one variety of aphasia. This was Wernicke’s aphasia, which occurred after lesions within a broadly defined left hemisphere Wernicke’s “zone” that included cortex and white matter tracts of the angular and supramarginal gyri and the posterior superior and middle temporal gyri [36]. Broca’s aphasia was simply mild Wernicke’s aphasia from a Wernicke zone lesion, coupled with dysarthria when the lesion extended beneath Broca’s area to the lenticular nucleus (caudate and putamen). Because it lay within the same vascular territory, the left third frontal convolution was often affected by a stroke that caused symptoms of Broca’s aphasia. However, injury to Broca’s area was incidental and irrelevant.
Wernicke zone lesions affected not just language but all aspects of intelligence dependent on didactic learning [37]. Alexia and agraphia did not exist apart from aphasia. Like Broca’s area, the angular gyrus had no special role: “One cannot recognize in the [angular gyrus] the role of the center for visual images of words” (p 500) [37].
Marie’s iconoclasm resonated with English neurologist Henry Head (1861–1940), who in 1926 published his monumental Aphasia and Kindred Disorders [39]. Studying patients with brain trauma suffered during World War I, Head conceived all aphasia as impairment in “symbolic formulation and expression” (vol 1, p 218) in which speech, reading, and writing were affected in concert. He denounced “diagram makers” like Bastian and Wernicke for “serene dogmatism” (vol 1, p 57) [39] and championed Hughlings Jackson’s writings.
Along similar lines, Kurt Goldstein (1878–1965), a pupil of Wernicke who worked in Germany and the United States, proposed that the fundamental impairment in brain-injured patients was in “abstract attitude.” Like Hughlings Jackson, Goldstein denied “a simple relation between a symptom and a lesion in a circumscribed area” (p 50) [40]. Symptoms were influenced by the “condition of the rest of the brain, and even of the whole organism” (p 256) [41].
Apraxia and Agraphia
Hugo Liepmann (1863–1925) in Berlin offered a theoretical framework for apraxia, disorders characterized by the failure to carry out motor tasks despite the ability to do so [42]. In 1907, Liepmann and Otto Maas (1874–1965) reported the case of a man with unilateral agraphia [43]. He had right-sided weakness. Despite normal speech and speech understanding, he was unable to follow commands requiring the use of his left arm. He could not write, copy text, or use anagram letters to spell his name. An autopsy showed damage from a large stroke in the distribution of the anterior cerebral artery. Involvement of the rostral corpus callosum and white matter tracts disrupted connections between anterior regions of the 2 cerebral hemispheres. Liepmann and Maas [43] attributed agraphia to apraxia of the left hand due to the disruption between motor cortex of the right hemisphere, which controlled left hand movements, and left hemisphere areas responsible for goal-oriented movements.
1965: Rediscovery and New Directions
There were exceptions, such as Solomon Henschen (1877–1930) in Sweden and Johannes Nielsen (1890–1969) in Los Angeles, but the center–pathway model fell out of vogue during the early and middle decades of the 20th century. Ascendant views of Marie, Head, and Goldstein were reinforced by the works of Swiss pathologist Constantin von Monakow (1853–1930) on diaschisis (focal brain lesions exerted distant effects) and the American psychologist Karl Lashley (1890–1958) on equipotentiality (one part of the cortex could take over when another part was damaged).
In Boston, Geschwind revived earlier formulations of alexia and agraphia based on Dejerine’s center-pathway model. He was inspired by unexpected findings described by Roger Sperry (1913–1994) in split-brain patients, who had undergone corpus collosotomy, the surgical separation of the 2 cerebral hemispheres, to control intractable epilepsy [44]. With neuropsychologist Edith Kaplan (1924–2009), Geschwind reported a patient with agraphia of the left hand, which they interpreted as a functional disconnection of the 2 cerebral hemispheres [45]. Delving into the older neurological literature, Geschwind was “troubled by the fact that people who had left their mark so indelibly in many areas of neurology, such as Wernicke, Bastian, Dejerine, Charcot, and many others, could apparently have shown what was asserted to be the sheerest naiveté and incompetence in the area of higher functions” (p 215) [46]. In his landmark article of 1965, “Disconnexion syndromes in animal and man,” [2] Geschwind discussed Dejerine’s case of alexia without agraphia [35] and Liepmann and Maas’s case of unilateral agraphia [43]. These cases and others were adduced in support of a critical role for pathway lesions in disconnecting functionally discrete cortical regions [2]. Geschwind reinterpreted the left angular gyrus as a center for visual-auditory associations required for memories of the “‘rules of translation’ from written to spoken language” (p 279) [2]. For alexia without agraphia, the disconnection was