Arm tremor, tardive dyskinesia, and mental retardation

The arm tremor of adults diagnosed as having mental retardation and/or tardive dyskinesia was examined through an analysis of the acceleration properties of several arm postures. The degree of arm acceleration was increased in all groups compared to a control group without mental retardation. The tardive dyskinesia and/or mentally retarded groups also showed a shift to a lower modal frequency of physiological tremor. Results showed that both time domain and frequency properties of the tremor acceleration signal are necessary to distinguish between groups. The neuroleptic medication appears to engender a dual and opposing influence on performance in the arm tremor task for the mentally retarded group. The medication reduces behavioral variability as indexed by analyses of arm acceleration over time (time domain) but lowers the modal frequency of physiological tremor.