Sex Differences in Brain Organization for Verbal and Non-Verbal Functions

Abstract

This chapter discusses sex differences in brain organization and functional brain asymmetry. It presents some data that may reduce some of the ambiguity inherent in both the normal and the neurological studies and provides an overview of the findings relating the incidence of aphasia and apraxia to locus of lesion within the hemisphere, followed by a more detailed description of the effects of unilateral lesions on verbal and nonverbal intelligence tests in nonaphasic patients. The study confirms that there are undoubtedly sex differences in brain organization for a variety of human abilities; however, these sex differences cannot be depicted simply in terms of male brains tending to be more asymmetrically organized than female brains. Basic speech and praxic motor function are at least as unilaterally organized in women as in men. Some additional verbal functions also follow this pattern, for example, word fluency. When brain organization is assessed by nonclinical methods, perceptual asymmetries are sometimes less striking in females than in males, whereas motor asymmetries appear similar in both sexes. In general, it appears that a more focused approach to the study of sex differences in brain organization, both in terms of specificity of function examined and in specificity of neuroanatomical locus, will provide better answers to the questions of individual differences in brain organization.