Date of Award:

5-1989

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Psychology

Committee Chair(s)

Damian McShane

Committee

Damian McShane

Committee

William R. Dobson

Committee

Phyllis Cole

Abstract

This study investigated the associations between (1) handedness (demonstrated preference of one hand for the performance of most unimanual tasks) and neuroanatomical asymmetry (measurable differences in width between the cerebral hemispheres) and (2) familial history of handedness (the presence of a left-handed sibling or parent of a right-handed subject) as an intervening factor in the relation between handedness and neuroanatomical asymmetry. Width measurements of the brain were derived from computerized tomographic (CT) films and grouped in to categories by hand preference (measured by the Edinburgh Handedness Inventory) and family history. The measurements of right (n=68), right with left-handed relatives (n=24), and left-handed (n=16) groups were then compared by width and other transformations of the brain measurements. Subjects were adults of both sexes who had been referred for neurologic examination and were diagnosed as free of major distorting brain pathology. Hemispheric widths were compared by group, as ratios (left÷right) and as differences (left-right).

Analysis of variance revealed significant differences between right-hemisphere widths at three percentages of brain length in the posterior occipital and temporal-parietal portion of the right hemisphere. The two right-handed groups had significantly smaller right-hemisphere measurements than the left group at 80% (p= .03), 75% (p= .012), and 60% (p= .029) of brain length. There were no significant left-hemisphere differences between the groups. In terms of ratios of sides and differences between sides in the same brain region, the left-handed group was different from the right-handed group at the p< .05 level at 80%, 75%, 67%, and 60% of brain length. The family history variable did not distinguish the two right-handed groups from each other. Overall, the right-handers had wider posterior-left hemispheres, left-handers had the same-sized left hemisphere as the right-handers, but the posterior-right hemisphere of the left-handers was bigger than that of the right-handers. The relatively larger right hemisphere of the left-handers made the brains of these subjects appear more symmetrical.

Handedness appears to be moderately associated with neuroanatomical asymmetry. The differences in sizes of brain structures and their relation to functionally lateralized abilities may shed light on the processes by which each hemisphere becomes specialized to perform specific tasks and other aspects of individual differences.

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