Crossed Laterality

All paired muscle systems are represented in the brain by paired controlling centres. Dominance, or leading control of the function, may be entirely leftsided, in which case the organs controlled are dominant on the right side, or entirely right-sided. If some centres are on the left and some on the right side of the brain, the condition is called crossed laterality. The dominance may be fixed, and diagnostic methods give no variation in results. In some children there is less fixity, one or the opposite centre taking control according to whim or circumstance. These investigations were provoked by the observation of educational problems arising in a school of 150 to 200 children of both sexes between the ages of 6 and 16. The observations and investigations were carried on over a period of four years. The examiner knew all the children intimately, and lived among them continually. Thorough physical examinations were made at intervals of approximately nine months. Intelligence was measured and remeasured, using Terman and Merrill's tests, and Raven's progressive matrices. The teaching staff of the school used to meet regularly and frequently for discussion of the progress, educational problems and conduct of each child. In the capacity of School Medical Officer I attended all such meetings. There were unrestricted opportunities for investigation of these problems. During the work report meetings it was noticed that some 40% of the children, at one time or another, presented some difficulty or failure in educational attainment. A further search revealed that 70°' of these children had some type of crossed laterality. Viewed from another aspect it was known that 4700 of the children in the school had crossed laterality, and of these 8500 were in the group who experienced difficulties in school work. The work here recorded was planned to discover: (1) Symptoms arising because of crossed laterality: (2) the effect of these symptoms on education; (3) the mechanism whereby these symptoms are produced; (4) why some cases of crossed laterality were asymptomatic; and (5) effective means whereby the handicap of crossed laterality might be overcome.