All forms of cerebral palsy are the result of anomaly, injury or disease of the brain, a part of the body of which the functions are so diverse and so difficult to evaluate as to allow for infinite variations of the condition. The functions of the brain are localized in the fully developed person, and brain cells are specialized with a high degree of differentiation. However, there is also an integration of these functions, so that disturbance of any differentiated function results in a necessity for a total reintegration. It is impossible to imagine that any two brains would show identical localization of function. The interrelation between the fundamental inherited automatic functions and the results of the tremendously varied environmental factors could and does bring about differences in total psychomotor behavior, even in identical twins.
All response is motor response. For example, the variations of laughter are so great there
PHELPS WM. THE MANAGEMENT OF THE CEREBRAL PALSIES. JAMA. 1941;117(19):1621-1625. doi:10.1001/jama.1941.72820450003012