We have found marked anatomical asymmetries between tile upper surfaces of the human right and left temporal lobes. The planum temporale (the area behind Hesch's gyrus) is larger on the left in 65 percent of brains; on the right it is larger in only 11 percent. The left planum is on the average one-third longer than the planum. This area makes up part of the temporal speech cortex, whose importance is well established on the basis of both anatomical findings in aphasic patients ans cortical stimulation at operation.

We report the neuroanatomical findings in 4 consecutively studied brains of men with developmental dyslexia. The patients, who ranged in age between 14 and 32 years, were diagnosed as dyslexic during life. Nonrighthandedness and several autoimmune and atopic illnesses were present in the personal and family histories. All brains showed developmental anomalies of the cerebral cortex. These consisted of neuronal ectopias and architectonic dysplasias located mainly in perisylvian regions and affecting predominantly the left hemisphere. Furthermore, all brains showed a deviation from the standard pattern of cerebral asymmetry characterized by symmetry of the planum temporale. The neuroanatomical findings in these 4 patients are discussed with reference to developmental cortical anomalies, cerebral asymmetries, reorganization of the brain after early lesions, and the association between learning disorders, left handedness, and diseases of the immune system.

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We report an experimental study designed to test the following hypothesis derived from clinical observations: There is an elevated frequency in left-handed individuals and in their families of immune disease, migraine, and developmental learning disorders. In two separate investigations the frequency ofthese conditions was compared -in strongly left-handed subjects and -in strongly right-handed controls. In each of the investigations we found markedly higher frequencies of immune disease in the lefthanders than in the rightphanders. The rate of learning disabilities was also much higher in the left-handers than in the right-handers in both investigations. In a second study the frequency of lefthandedness was compared in patients with migraine or immune disease and in general population control subjects free of these disorders. There was' a higher frequency of left-handedness in patients with migraine and myasthenia gravis than in controls. We present a brief outline of a hypothesis that may account for an increased frequency of immune disease in left-handers and in their families.Cerebral dominance-i. e., greater proficiency ofeach cerebral hemisphere in acquisition and performance of certain specific functions-has been recognized as a biological characteristic of humans' for over 100 years. In most people there is dominance ofthe left hemisphere for language and ofthe right side for certain spatial functions. The older literature dealt predominantly with humans, with major stress on the laterality of lesions producing certain cognitive deficits. Since World War H' there have been many studies that demonstrate dominance in normals.By contrast, few studies on laterality deal with the kinds of data that are often found in studies ofother biological traits, such as eye color. Examples of such data include the anatomical structures involved, biochemical and' immunological properties, genetics, ontogeny, evolution, and comparative features in other species. In older publications one finds a few discussions ofassociations ofhandedness, such as asymmetries in fingerprints (1). More recent studies deal with anatomical asymmetries in the human brain, especially in language areas (2-6), asymmetries of function and structure in other species (7-11), the genetics of handedness (10, 12, 13), and the relationship of sinistrality to learning disabilities and to artistic, athletic, and other -talents (12,14). Anatomical maldevelopment has been demonstrated in the left side of the cortex (15) and in the thalamus (16) of a left-handed childhood dyslexic. These studies reflect growing interest in the' biological associations of dominance.Since the autumn of 1980, one of us (N.G.) has been impressed by observations on both patients and normals with an apparently elevated frequency ofcertain disorders in left-handers and in their families, including immune disorders (e.g., ulcerative colitis, celiac disease, and Hashimoto's thyroiditis) and migraine. Developmental learning disorders (e. g., dyslexia and stuttering) were als...

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Structural asymmetries between the hemispheres are found in the human brain. Asymmetries in the auditory regions and in the Sylvian fissures are present even in the fetus. The Sylvian asymmetries may have existed in Neanderthal man and are found consistently in some apes. They may relate to right-left differences infunction. Thus, the striking auditory asymmetries could underlie language lateralization. The asymmetries in the frontal and occipital lobes and the lateral ventricles are correlated with hand preference. Anatomical asymmetries may help to explain the range of human talents, recovery from acquired disorders of language function, certain childhood learning disabilities, some dementing illnesses of middle life, and the evidence for behavioral lateralization in nonhuman primates.

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