Brain7 reported a series of patients with right cerebral tumors whose visual disorientation disabilities were greater than their other defects. Heimburger and Reitan21 suggested that tumors might be lateralized to the left or to the right depending on whether the patient had more difficulty with writing or drawing. Although localization studies on tumor patients are notorious for pressure and other secondary symptoms, support has come from studies of patients with circumscribed injuries or infarction. For example, Olsen's29 patient with a right parietal thrombosis had visual agnosia but had excellent visual acuity, played the piano and conversed well. Especially notable are studies by modern neuropsychologists: Paterson and Zangwill31 emphasized the importance of the right hemisphere in constructional apraxia, a conclusion supported by Piercy and Smyth32 in their recent review of this subject. Hécaen and Angelergues20 found that of 18 unilateral lesions with agnosia for faces, 16 were on the right side; of the remaining 2 patients, one was known to be left-handed. Teuber36 found visual seizures in 15 patients, the injury being predominantly right-sided in 13 cases. Delimitation of the lesions is perhaps more exact with surgical removals such as temporal lobectomy: Milner24 found verbal deficits following left-sided ablations and visuospatial deficits on the right.‡
It was suggested by Bard and Brooks3 that acceptance of the localization of a particular function to a particular area requires affirmative as well as negative evidence. That is, not only must there be loss of the function with injury to the specific area, but there should also be preservation of the function when the specific area remains intact in the event of widespread surrounding loss. Such a criterion is particularly relevant here since Denny-Brown10,11 has pointed out that certain visuospatial (which he terms morphosynthetic) processes in the left hemisphere may suffer losses difficult to demonstrate because of the more important losses in certain language (propositional) processes.
Affirmative evidence for lateralization of visuospatial function was found by Mullan and Penfield:25 in 217 patients with temporal lobe epilepsy, 12 had visual illusions, arising in 11 cases from the hemisphere minor for handedness.
Affirmative evidence of visuospatial dominance in the minor hemisphere has recently become available from 2 of our patients who had complete section of the corpus callosum and anterior commissure for the treatment of seizures.§ The first patient's clinical history and surgery have been discussed before in detail.5,6,15,16 Our second patient was operated upon in September 1963, and has had a smooth postoperative course with complete relief of convulsions to date; a more detailed report is in preparation.4 Both of these patients, W. J., a 48-year-old man, and N. G., a 30-year-old woman, were always right-handed and right-footed and without left-handed near-relatives except N. G.'s maternal uncle.
We are grateful to Professors R. W. Sperry and P. J. Vogel for their continuing criticisms and encouragement.
AkelaitisA. J. Studies on the corpus callosum. VII. Study of language functions (tactile and visual lexia and graphia) unilaterally following section of the corpus callosum. J. Neuropath. exp. Neurol.19432: 226–262.AkelaitisJ. Neuropath. exp. Neurol.2:226–262.
BardP.BrooksC. M. Localized cortical control of some postural reactions in the cat and rat together with evidence that small cortical remnants may function normally. Res. Publ. Ass. nerv. ment. Dis.193413: 107–157.BardBrooksRes. Publ. Ass. nerv. ment. Dis.13:107–157.
CritchleyM. Speech and speech-loss in relation to the duality of the brain. In: Interhemispheric relations and cerebral dominance. V. B. MountcastleEd. Baltimore: Johns Hopkins Press1962x294 pp. (see pp. 208–213).CritchleyInterhemispheric relations and cerebral dominance
HécaenH. Clinical symptomatology in right and left hemispheric lesions. In: Interhemispheric relations and cerebral dominance. V. B. MountcastleEd. Baltimore: Johns Hopkins Press1962x294 pp. (see pp. 215–243).HécaenInterhemispheric relations and cerebral dominance
JacksonJ. H. Notes on the physiology and pathology of the nervous system. “Coarse” disease of the brain and optic neuritis. In: Selected writings of John Hughlings Jackson. J. TaylorEd. New York: Basic Books Inc.19582: 215–237 (see p. 220).JacksonSelected writings of John Hughlings Jackson2:215–237 (see p. 220).
It should be pointed out that the difference is one of degree, just as the left hemisphere is dominant rather than exclusive in language function. See Nielsen,28 Subirana,35 Zangwill,38 Critchley,9 on the role of the minor hemisphere in language and the more general question of relative dominance.
Part of the relevant data has been presented as part of an extended discussion of visual perception following commissurotomy (Gazzaniga et al.14).