The earliest motor activity of the normal infant of any vertebrate form is relatively simple and stereotyped in pattern. Later, with the functional and anatomic development of the motor cortex, increased complexity of skilled and coordinated movement appears. This is particularly evident in primates—monkeys, chimpanzees and man— since prehensile finger movements occur in these forms. The paralysis which follows destruction of the motor cortex in man may appear as a "cerebral palsy" after birth injury, or as a hemiparesis in the adult. In all primate forms destruction of a specific motor region is followed by a specific and predictable motor deficit, but the present study indicates that the age of the individual directly affects the deficit in subhuman primates and in man, since removal of a known cortical area from the infant causes a paralysis of different quality from that which occurs after a similar cortical ablation in an
KENNARD MA. RELATION OF AGE TO MOTOR IMPAIRMENT IN MAN AND IN SUBHUMAN PRIMATES. Arch NeurPsych. 1940;44(2):377–397. doi:10.1001/archneurpsyc.1940.02280080137008
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