Chapter 13 Familial Sinistrality and Cerebral Organization

Abstract

Familial sinistrality (FS) is an important variable for understanding cerebral organization. The dichotic language task studies fail to suggest clear differences between FS - and FS + persons, regardless of their handedness. The tachistoscopic studies suggest lesser left hemisphere dominance for language function in both right-handed with FS (RHFS +) and left-hander without FS (LHFS -) persons. Recent studies suggest that different aspects of language function may be more laterally dissociated in the FS + than in the FS -, but further study of this is needed. Tachistoscopic studies also suggest that FS + acts to reduce right hemisphere specialization for visuospatial functions in right-handed persons, and may do so in lefthanders as well. FS has been found to be poorly related to hand preference, hand skill, or eyedness, thereby suggesting that motor laterality characteristics are largely independent of FS. FS is related to handwriting posture in left-handed persons, with the inverted writers having significantly more lefthanders among their first plus second-degree relatives. This greater incidence of left-handedness occurs mainly within the maternal family line. The incidence of FS, when FS status (FS + or FS -) is defined by the presence of at least one first degree relative, is significantly, but very slightly, greater in right-handed females than males (about 37% versus 33%) and in left-handed females than males (about 52% to 47%). A tentative general inference that FS + may influence visually mediated processes more than auditory and motor processes may be advanced in view of this set of conclusions.