Instability in functional motor laterality of children and adolescents with endogenous psychosis and predominantly motor disturbances.

A group of eight unmediated right-handed children and adolescents with endogenous psychosis and predominantly motor disturbances and two right-handed control groups (6 healthy subjects and 10 patients with different psychiatric diseases) were investigated with the help of a tapping-test series. The most important finding was related to differences in the stability of functional motor laterality between controls and psychotics. Stability of instability in functional motor laterality was identified by referring to the standard deviation (SD) of percentile right-left tapping differences calculated for each subject for the various parts of the tapping-test series. The high SDs in psychotics, in contrast to the low SDs in both control groups, point to increased variations or instabilities in the functional superiority of the preferred hand. Instability in functional motor laterality in this test is considered characteristic of this subgroup of patients, and may be due to a partial relapse to a lower hierarchical stage of handedness.