Mechanisms and Development of Cerebral Lateralization in Children

Abstract

The sequences of cognitive development to be considered in this discussion culminate in an endpoint of lateralization in the mature human nervous system that in its broad definition is no longer in dispute. In the right-handed majority, language-related processes are left lateralized in almost every case. The right hemisphere does contribute toward certain aspects of verbal behavior, however (Hecaen, 1978; Searleman, 1977, 1983), notably comprehension of logical relationships, inference, metaphor, and humor (Beeman, 1993; Gardner, Ling, Flamm, & Silverman, 1975), and at the output stage, intonation, particularly when it reflects the emotional tone of the utterance (Ross & Mesulam, 1979). The left hemisphere is also specialized for rapid sequential recognition of familiar input, nonverbal as well as verbal, and also the recall and recognition of order information and the formulation of action plans, both motor and conceptual. Right hemisphere dominance is best documented for certain spatial-relational processes, particularly in the visual modality, and for the processing of emotional information (Kinsbourne, 1982). Non-right-handers deviate from the dextral norm in the following manner: in addition to left-sided representation of language, which is as prevalent in non-right-handers as in right-handers, language is also represented on the right in up to 70% of the cases (Gloning, Gloning, Haub, & Quatember, 1959). In non-right-handers, spatial-relational functions are right lateralized as in right-handers, but involve the left hemisphere also in more than half of all instances (Bryden Hecaen, & DeAgostini, 1983). Within each hemisphere the territory involved in cognitive function is more extensive in the left-than the right-hander (Kinsbourne, unpublished analysis of data from Bryden et al., 1983). Gender-related differences in lateralization are more contentious (Lewis & Harris, 1990), and the claim that language and visuospatial functions are more bilateralized in females than males, and even that left intrahemispheric organization differs between the sexes, are not yet well substantiated. With respect to development, existing knowledge is virtually restricted to language functions on the one hand and spatial-relational functions on the other. This discussion will therefore be confined to considering how peripheral laterality, notably hand preference, is established in the developing child, and how the differential hemispheric representation of language and spatial-relational functions develops, first in the normal case, and then in certain types of developmental disability.